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441 Cards in this Set
- Front
- Back
- 3rd side (hint)
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How many gallons in a barrel of oil?
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42 gallons
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how much oil does the USA import a day?
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roughly $9,000,000
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How is petroleum geology defined?
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it's the application of geology and it's related fields to the exploration and exploitation of hydrocarbons. It can involve seismic, well logs, and samples
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Who do geologists work with?
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Geophysicits, geochemists, petroleum engineers, business and risk analysis, and management
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What are resources?
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a geologists (optimitic) opinion of ALL the undiscovered oil that is theoretically present in the area. Conservative bankers will not loan money of resrouces, investment bankers might
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What are reserves?
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an engineers (conservative) opinions of how much oil is known to be producible within a known time, known techniques, known costs, and known fields. Conservative bankers will loan money on reserves
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What are the categories of reserves?
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Active and Inactive
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What are active reserves?
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producilbe within the foreseable future (~20 years or less)
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What are inactive reserves?
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these are resources known to exist, but not considered producible within 20 years. They're inaccessible or producible with known commercial methods (EOR). conservative bankers won't loan money on this, less conservative organizations will fund research to investigate these EOR methods
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How many liters of oil in a barrel?
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159 liters
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How much oil does saudi arabia contain in reserves?
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261 billion barrels
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How much oil does Prudhoe Bay Alaska contain in reserves?
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24 billion barrels
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How much oil does the domestic United States contain in reserves?
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23 billion barrels
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How often are wildcat wells successful?
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10%
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When are where were the first oil wells drilled?
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China in 347 AD. They were up to 800ft deep and ddrilled with bits attached to bamboo poles
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When and where was the first modern oil well drilled?
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Asia, Aspheron Peninsula northeast of Baku in 1848
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When and why was natural gas first used?
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1854. It was produced from a water well in Stockton, California. They used it to light the courthouse
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What was oil first used for?
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to protect the bottoms of ships from Shipworms (tredolites) and to waterproof them
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What was first used for candles? why?
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blubber from sperm whales because it was a favorable aromatic
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why was blubber phased out?
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Over-fishing of sperm whales, dwindled the population, and hardly any were left in the atlantic ocean.
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When was kerosene first distilled from oil?
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1849 by Dr. Abraham Gesner
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When were blubber lamps off the market? what replaced them?
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kerosene lamps replaced them in 1857. created a market for oil
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When was the first oilwell drilled in North America? Where?
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1858, Oil Springs, Ontario, Canada
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Where was the first oil well in the USA? when? who drilled it?
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Titusville, PA; 1859, Colonel Edwin Drake
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What caused price swings during the beginning of oil drilling?
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uncontrolled drilling and non-unitized drilling created underproduction of fields
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What was the huge oil gusher in Texas?
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Spindletop located in Beaumont, TX. It gushed 750,000-100,000bbl/day due to no BOPs. Happened January 10, 1901
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Who is credited with Spindeltop?
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Texaco, Mobil, Gulf, and Humble
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Who created Standard Oil and why?
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John D Rockefeller to control the whole oil business, and stabilize production and prices
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If oil was cheap, they made money on processing (downstream)
If oil was expensive they made money on production (upstream) |
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What was Standard oil violating in 1911?
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The 1891 Sherman antitrust act, which was about monopoly laws. standard oil controlled 84% of all the crude oil in the USA
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they had excessive restrictions to trade, bought out small independent refiners, and lowered prices in regions to force bankruptcy of competitors
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What were the offspring from Standard Oil dismantling? (hint 7)
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Standard oil of New Jersey (Exxon), St. oil of New York (mobil), SO of california (socal which became chevron), SO of ohio (sohio absorbed by BP), SO of indiana (amoco), continental oil (conoco) Atlantic (arco)
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What were the major 2000 mergers?
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Exxon + Mobil
Chevron + Texaco + Unocal BP + amoco + arco Conoco + philips |
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What events drove the demand for oil up?
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the invention of henry ford's model T (mass production of cars) cars required oil. WWI and WWII
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What were the 7 sisters in the 1920s?
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BP, Shell, Exxon, Gulf, Texaco, Mobil, and Chevron
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What are the major companies now?
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Shell, BP, Exxon-Mobil, and Chevron
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Where does oil and gas production mainly occur?
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Sedimentary basins
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What controls 94% of the world's oil reserves?
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national oil companies. The first publicly traded company on the list is exxon at number 13.
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When were prices stable? When was the first spike?
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1880s-1970s oil was relatively stable due to Standard oil. Prices first spiked in 1970s due to OPEC restricting reserves
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When was the famous bust?
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1980s-1990s due to flooding of the market
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What caused booms and busts? Has this changed?
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politics and political events, not supply and demand. this has changed though
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What is causing todays oil crisis?
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China and India becoming industrialized and needing lots of oil. This is driving the demand up and prices are increasing. OPEC can no longer control the market due to this high demand
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What is our current worldwide consumption in percentages of energy?
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Oil 40%
Natural gas 24% Coal 22% Nuclear 7% Renewables (solar, wind, geothermal) 7% |
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How much energy in the US is supplied by fossil fuels?
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84%. however, natural gas will increase due to the current production
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Examples of upstream vs. downstream
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Petroleum geologists are upstream, (exploration and exploitation of oil and gas). Environmental geologists are downstream (clean-up) along with refining and distribution
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How much oil does the USA use on a daily basis?
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20 million barrels a day
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Is it problematic that the USA used 20 million bbl/day?
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Yes. our usage is larger than production, and there is speculation that we will cease oil exploitation and exploration by 2040.
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What years was the most oil ever found?
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1940s
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What are the problems with alternative energy sources?
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no infrastructure, and there is not enough capital behind them to support their development
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What is a major consumer of fossil fuels?
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the transporation industry.
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What is ineffiecient about transportation?
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only about 15% of the fuel put into a vehicle is used for powering the wheels to turn. The other percentage is lost due to heating, braking, and other ineffieincies
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Why do british use less fossil fuels?
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because Margaret Thatcher shut down the coal mining industry and switched to nuclear. only use north sea oil for exporting
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What is France's energy consumption like?
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france is the largest electricity producer from nuclear power plants in Europ. 78% of their power is nuclear, and they export 18% of their electricity
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What is germany's energy situation?
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lots of homes are solar powered. They store electicity on the grid when it's not being used, and this electricity can be pulled off the grid whenever needed
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What is included in the petroleum system?
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Source rock, Reservoir rock, trap, seal, and charge (charging of reservoir)
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What is needed to charge a trap?
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generation of oil and migration of oil into the trap
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Do all basins generate oil?
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No. many basins do not have effective generation, or generation occured at the wrong time to charge the traps. Some basins do not produce oil and other have prolific generation
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What are the methods that people have used to figure out where oil is?
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Charge analysis, oil systems analysis, or petroleum systems.
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What is a basin and how does it form?
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A basin in a low area of the earth's surface that fills with sediment and sedimentary rocks. These are caused by plate tectonics
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What is the USGS definition of a petroleum system?
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Essential elements, processes and genetically related petroleum whose provenance is a single pod of active source rock
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Why is geochemistry important in the petroleum system?
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It's useful for determining the source rock, the type of oil present, and where the petroleum has migrated to and from
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According to the USGS what are the essential elements of a petroleum system?
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Source rock, reservoir, seal, overburden (needed for thermal maturity) this Results in all strata overlying the source rock to be part of the petroleum system whether the contain petroleum or not.
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What is the oil window?
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This is the perfect, goldilocks zone for oil generation. It contains the perfect temperatures and pressures for oil generation. Above or below this window, pressures and temperatures can be too high or low for oil generation
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What are the components of petroleum accumulation?
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source (oil, gas, and charge), trapping geometry, reservoir, and seal. hydrocarbons migrate from source to reservoir if there's a trap and seal
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What tends to produce natural gas?
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woody plants
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What are source rocks?
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These are typically organic rich shales that 'cook' and form hydrocarbons from the remains of micro-organisms like algae and protozoans. these can be marine or non marine
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What is an oil precursor?
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Kerogen is formed from flesh and is the precursor to oil
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What can happen if kerogen is cooked too long?
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If it's too high of a temperature or too long, it can be turned into organic compounds with progressively fewer hydrogen atoms (pure carbon or graphite)
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What happens as shales cook?
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They generate their own porosity. 50-60%
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How does oil escape the source rock?
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Fracturing allows the pores to connect and this creates pathways for hydrocarbon migration
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Why do we need to know the burial history?
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need to known time and temperature that the source interval experienced to see if it contains oil and gas. (ie was it buried for too long at too hihg of a temp or was it singed? uplift can bring source rocks out of the oil and gas window. source can also become overcooked)
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Can we have gas that's created from sediments?
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Yes! shallow gas cn be created by bacteria that lives in the subsurface. This becomes biogenic methane (bogs, lagoons, and bayous. that's why they stink)
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What are the types of structural traps?
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Anticline, Fault, and diapir
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What are the types of stratigraphic traps?
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Pinch out, unconformity, and sand lenses
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What do we need for a reservoir?
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Porous sandstone or carbonate
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What is a seal?
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It's a non-permeable bed (or fault) that caps the petroleum accumulation
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What is commonly needed to form a seal?
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Structural deformation of tectonic events
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Why is timing critical in petroleum accumulation?
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Formation of the trap cannot occur before sealing facies are deposited. oil must be generated after the trap is formed. Traps and seals cannot be breached (leak)
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How was subsurface determined in early days? what was a problem with this?
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Subsurface was mapped using surface structures. This was problematic because what if there are no surficial expressions or it's underwater
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how does seismic help us?
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We use seismic to map the subsurface stratigraphy and faulting
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What is the problem with well logs? and how do we overcome this?
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they only give us a discrete vertical sample. so we correlate multiple well logs to help determine 3D structures
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What is a shared risk factor?
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the presence of a source rock because if no oil has been generated, you can never have a prospect
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What is an independent risk factor?
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the presence of a reservoir, trap, or seal because if one prospect is dry in the system, another may contain hydrocarbons
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From what temperatures does basic diagenesis occur?
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0-100 degrees celcius
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what temperatures is the oil window?
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100-200 degrees celcius
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What temperature is the gas window?
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200-250 degrees celcius
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What occurs after 250 degrees celcius?
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metagenesis (metamorphosis)
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What are the major questions one must ask to come up with a prospect? (6)
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Is there a source? is the source rock able to generate oil or gas? what is the maturity of the source rock? is there are pathway for hydrocarbon migration to charge a reservoir? are there reservoir traps and seals? is the hydrocarbon accumulation economic?
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What are the two categories of drilling?
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Exploration and Production
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In basic terms, what does an oil rig consist of?
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Derrick, mud system, kelly, blocks, draw works, engine, BOP
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What is the space between the drill pipe and the hole called?
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the annulus
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What is mud systems primary purpose?
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to cool the drill bit, circulate the hole, bring up cuttings, and maintain pressure
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What purpose do the mud and BOP serve?
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to maintain the pressure and prevent blowouts
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Why is biostratigraphy work hard?
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it is difficult to determine the age of a rock based on fossils from drilling due to cavings, reworking, and redeposition of fossils
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What do mudlogs contain?
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A description of lithology, porosity, measurement of fluorescence, description of the rate of penetration, and the measurement of gas while drilling
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Why are core samples valuable?
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They provide the best but expensive representation of the rock. can be used to determine facies and environment of deposition
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How is porosity defined?
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It's the measurement of pore space between or within grains. It's expressed as a percent. usually ranges 0-30%
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How is permeability defined?
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It's a measurement of the tortuosity of flow paths. It's expressed by Darcy's law.
Q=(K(p1-p2)A)/(uL) |
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What is capillary pressure?
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it is a function of pore throat size, fluid viscosity, and wettability. Increasing capillary pressure results from pore diameter decreasing
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What does surface casing prevent?
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freshwater aquifer contamination and fracturing of shallower units as fluid pressure of the mud increases
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How is casing set, and what happens after casing a hole?
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Casing is set based on estimation of pressures at specific depths (determined from leak off tests of DSTs). After casing, zones are picked for perforation
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What do well headers contain?
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well name, location, elevation of kelly bushing, depth drilled, mud parameters, bottomhole temperature, casing points, bit size, log types, and date
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What is the general conductivity of fluids used in drilling?
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Saltwater is more conductive. Freshwater is less conductive making it more resistive. Hydrocarbons are very resistive
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What is the caliper log?
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measurement of the hole diameter. It's calibrated to the bit diameter. Holes can expand if there's soft rock, that's highly fractured, or contract is the sides of the hole become caked with mud
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If the caliper shows the hole diameter is smaller than the bit diameter, what does this tell us?
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That the unit is porous, and the mud column pressure exceeds the formation pressure. Mud invades the formation and builds up on the wall
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What does the SP log measure?
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The spontaneous potential measures changes in electric potential between the borehole and a surface voltmeter
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What does the SP log require?
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to run an SP, the hole must be open (not cased) and a conductive mud (saltwater mud) must be used
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What does the SP tool depend on?
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The conductivity of the mud and formation
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For a normal SP, what units are positive/negative?
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Sand is negative and shale is positive
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What will give us a normal SP reading?
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when the salinity of the mud is less than the salinity of the formation water
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What gives us an inverted SP reading?
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if the salinity of the mud is greater than the salinity of the formation water
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What will give us a suppressed SP value?
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if the salinity of the mud is equal to the salinity of the formation water
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What are the three types of resistivity logs?
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Normal,induction, and laterolog
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What is a laterolog?
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It's a resistivity log that shoots an electric current into a rock then measures the response within the formation. It focuses the electrodes using two electric fields on either side of the zone of interest.
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What is an induction log?
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a resistivity log that induces an electrical field with a magnet.
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What will a permeable formation full of oil, gas, or freshwater look like on a resistivity profile?
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It will show a high resistivity and negative SP values
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What will a permeable formation full of salt water look like on a resistivity log?
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The resistivity will be low, but the SP will show negative, indicating it's a sandstone, but since there is saltwater, it's conductive, not resistive
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When looking at the shallow, medium, and deep resistivity curves, what indicates hydrocarbons?
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If there's separation of the shallow and deep, and the deep curve indicates a higher resistivity. Rmf<Rw and Rxo<Rt
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What is a microlog?
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a pad device that indicates permeable formations based on mud invasion
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What is Archie's equation?
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it is used to calculate the percent of oil vs. water saturation.
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What does a gamma ray log measure?
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It measures the natural radioactivity of the rocks. It's measured in API units
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What are spectral gamma rays?
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These are gamma rays that distinguish radioactivity from U, Th, and K to help determine mineralogy, and composition of high gamma rocks
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What are some reasons a sandstone on a gamma ray might have divets in its profile?
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It might contain intermittent shales or it can have mud rip-up clasts (like those in a channel lag) this isn't as common though
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What does a funnel shape gamma ray profile indicate?
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that's it's coarsening upwards, so it's likely a delta
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What does a bell shaped gamma ray profile indicate
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That it is fining up, so it is likely a fluvial channel
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What is a radioactivity log, and what are the two types?
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It's a log that fires neutrons or gamma rays into the formation. There are neutron and density radioactivity logs
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How do neutron logs work?
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They bombard the rock with a radioactive source. Hydrogen atoms then release their own gamma rays. Since different fluids have different hydrogen contents, they each have their own signature.
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What does a high count on the neutron log indicate?
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Porosity, and fluids like oil, gas, and/or water because they have hydrogen, whereas most rocks do not
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How does a density log work?
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it emits gamma radiation and reads gamma radiation returned from the formation. It's sensitive to the density of excitable electrons and is a function of rock density and porosity
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What does a separation of the neutron and density logs indicate vs. non separation
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separation indicates a gas zone. the density overestimates porosity and the neutron underestimates porosity. No separation means it's likely oil or water
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How does an acoustic log work?
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It shoots sounds or clicks into the formation and measures the interval transit time. Faster speeds occur in hard rocks (older). Slow speeds in more porous rocks.
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What is a dip meter log?
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it's a micro-resistivity too that measures the dip of beds.
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What it a FMI log?
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images the beds, fractures, faults, and other sedimentary features. It's very useful for evaluating thin bed plays.
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What is a photoelectric log (PE)?
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a kind of density logging tool. records the absoption of low energy gamma rays by the formation, and obtains the atomic number to directly tell us mineralogy
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What does the highest gamma ray response correspond to?
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A marine transgression
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Describe hanging a well log
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well logs are typically 'hung' on a structural or stratigraphic datum. Can also be hung on sea level If hung on a structure, it's hard to determine the structures present. If hung on stratigraphic line, it's easier to see structures.
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When dealing with velocity, what is the ranking of rocks speed, slowest to fastest?
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Sandstone, shale, carbonate, dolomite, evaporites
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How does porosity effect velocity?
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If a rock is porous the velocity decreases. Velocity increases as porosity decreases. Porosity typically decreases with depth
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How does mineralogy affect porosity?
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Island arcs (like Japan) have higher amounts or plag, arkose, and metamorphic fragments. These decrease the porosity of the rock because they compact more readily than quartz (which is harder)
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Why does the input pulse normalize and reverse?
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It depends on if you are going from fast to slow media or vice versa. When we go from slow to fast, we get a positive reflection coefficient. When we go from fast to slow we get a negative coefficient
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What is the seismic trace and how can it vary?
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the seismic trace is what we get as an outcome from the input pulse going through the rock column. This can change if the rock is faster or slower than the original input pulse
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What is polarity?
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polarity is used to see if you're going from fast to slow to fast or slow to fast to slow to determine if a layer is fast of slow. If we know something about the reflection, we can determine the polarity
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What is multi-component seismic?
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it collects both P and S waves. It uses hydrophones for compressional waves and particle motion detectors for shear waves. Shear waves do not pass through water, that's why it's necessary to have both
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Why is it tricky to collect 3D seismic?
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because all the receivers must be in a perfectly straight line and perfectly spaced apart.
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What is 3D seismic composed of?
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Crosslines and Inlines
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What is a crossline?
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a seismic line within a 3D survey, perpendicular to the direction in which the data was aquired
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What is an inline?
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a seismic line within a 3D survey, parallel to the direction in which the data was acquired. In marine seismic data, the inline direction is that in which the recording vessels tow the streamers
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What causes a seismic reflection?
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When there are changes in density and velocity between 2 rocks of different properties. Compressional waves pass through and detect these
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What are some problems with collecting seismic data?
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we shoot the signal and it hits a point and comes back. We can only obtain data from an angle, not straight down from the receiver. So all data is collected and produced at an angle. it is also collected at different times because we shoot seismic several times to image a surface
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After the collection of seismic data, how is the information processed?
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since the receiver gets later and later in time, this results in a hyperbolic curve. We don't want a curve, so we flatten out the data along a certain distinct feature. This is done through mathematic equations known as stacking velocity. By stacking velocity, we make the signal louder, and this enhances the signal to noise ratio
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What is AVO?
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Amplitude Versus Offset. It is the same info from the same place, however, there are changes in signal due to fluids present. This might occur also because the signal hits layers at different angles. Fluids change these properties. We can look at pre-stacked to help determine these fluids and their transitions
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After the series of mathematical equations, called stacking velocity, what must be done to create a seismic line?
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A short range of velocities gives us straight layers and wide ranges give us squiggly, messy lines. We have to cut off all the noise and add the info together to create a line. from there we can interpret structures
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Is seismic collected in feet/depth?
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No, seismic is collected in seconds and must be converted to feet. Typically 1 second= 1km or 1 millisecond= 1 meter
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What is seismic migration?
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taking reflection and putting them in their correct positions
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What is multiple suppression?
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it is the process of removing artifacts of the seismic imaging certain features twice (like the seafloor)
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what is gain control?
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it is where we turn up the loudness of seismic signals
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What is the bowtie effect?
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it is where points of seismic data are in the wrong place due to dipping horizons. Migration is necessary to steepen and move the reflections into their proper spatial location
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What is the process of 'untying' bowties in a seismic line?
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post stack migration. if there are bowties, we can tell that the data is unmigrated
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why is it bad to use unmigrated seismic data?
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we might misinterpret features, like the location of faults or if anticlines are present
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Why do reflections get broader when they are deeper in the section?
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long wavelength seismic pulses penetrate deeper and seismic resolution decreases with depth
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What is a velocity pull-up?
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It's an artifact created in sedimentary rocks when the signal passes through a very fast rock (like salt). The reflection pulls up and appears to be an anticline
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What is a horizon slice and what is it useful for?
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picked on a certain geologic horizon. they are better for surface mapping
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What is a time slice and what is it useful for?
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they are picked from an exact time, not a stratigraphic layer/reflection. it's useful for determining structure
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Which waves in seismic image fluids better?
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Shear waves image fluids better because compressional waves can be washed out by fluids
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What are some applications of multi-component P-S imaging?
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reduces strong P wave multiples, helps identify fracture orientation and density, S waves are unaffected by pore fluids so it reduces offset of gas seepages,or fluid offset vs non-fluid offset, good for time-lapse or 4D monitoring, and direct hydrocarbon and lithology indicator
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What is 4D seismic and what is it used for?
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it's successive seismic surveys over a short period of time. they are typically used to image hydrocarbon fluid changes
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How do we distinguish a time slice from a photo?
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a time slice will have vertical stripes
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What is illumination in 3D seismic?
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it's like changing the light direction on a time slice of data. We are able to see other features in which we wouldn't see otherwise by changing the 'light' direction
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What is coherence?
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it is a time slice that's good for finding faults, sharp boundaries and structure. It's not a good lithology detector, but we do get the edges of the rocks
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How will time slices and horizon slices be the same?
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if the stratal layers are completely flat
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what is continuity data used for?
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it is useful for determining faults
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what is amplitude data used for?
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it is used to determine lithology
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What is the problem with seismic data in imaging thin beds or pinchouts?
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seismic data has a low resolution, and as thickness gets smaller, there are more seismic traces, so these signals can interfere with one another and cancel each other out because there is a strong bottom and strong top reflection
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What are the types of multiples?
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peg leg and multiple reflection
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What is a peg-leg multiple?
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a short path multiple or multiply reflected surface having an asymmetric path. they come from shallow subsurface features. They can be suppressed by processing
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What is a multiple reflection?
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reflected seismic energy or any event in seismic data that has occurred in one or more reflections. (ie imaging seafloor twice)
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What is the fresnal zone and what does it tell us?
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it's the spatial resolution. it indicates the deeper the data, the more difficult it is to detect a feature unless it's extremely large.
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What do reflection terminations indicate?
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stratal discontinuities or lapout
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What are depositional sequences?
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sequence of events bounded by nonconformity and their correlative conformity
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What does chronostratigraphic significance mean?
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that stratal surfaces have significance in geologic time
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What did pete vail say in 1977?
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Primary seismic reflections are generated by stratal surfaces which are chronostratigraphic rather than by boundaries of arbitrarily defined lithostratigraphic units
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What does stacking do?
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enhances the ability to see subtle changes across beds or other stratal boundaries
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What is the difference between facies and seismic?
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Facies are within clinoforms, and clinoforms are imaged by seismic.
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What is lapout and what is it used for?
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it's the termination of reflections, and it's used to separate apparently conformable sedimentary units
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Why do we use shazam lines?
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because beds might interfinger and there is no true boundary that marks the bed's termination.
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In an ideal slug model, how many reservoirs are there, and what are they?
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there are 4. the channels, lowstand wedge sands, lowstand deepwater fans, and the shelf slope break
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What did exxon develop in the 1970s and 80s? how were they able to develop this?
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they theorized there were synchronous global changes in sea level mainly due to tectonics. they were able to do this because they had data from around the world?
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What was the theory behind reservoir sands and source rocks exxon developed in 80s?
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reservoir sands were deposited during falls when the shelf was exposed and the continents were covered with glaciers. Source rocks were deposited during rises in sea level when the shelf was drowned and there were no ice sheets
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What are Wheeler Diagrams?
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diagrams that represent geologic time, erosion, deposition, and hiatuses.
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What are Wilson cycles?
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sea level rises and falls that correspond the super continents. Assembly of super continents means lower sea level, and breakup of these super continents correlates to higher sea level
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What are sloss sequences?
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2nd order sea level curves that is related to pulses of tectonism
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In the Quaternary, how much change has there been in sea level and why?
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in past 500,000 years sea level has changed 160 m. this is due to glacio-eustatic curves caused by Milankovitch cycles, proven by ice core oxygen isotope analysis
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What groups are hydrocarbons divided into?
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natural gas, oil, bitumen, and kerogen
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What is natural gas divided into?
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sour gas and biogenic gas
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What is oil divided into?
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sour crude, sweet crude, condensates, and natural gas liquids
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what is kerogen divided into?
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geopolymers (kerogen) and biopolymers (lipids, carbohydrates and proteins)
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What is present in hydrocarbons in greatest to least ranking?
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carbon, hydrogen, sulfur, oxygen, nitrogen, and others
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What is the simplest hydrocarbon?
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methane CH4
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What group are compounds with single bonds?
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alkanes or paraffins
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What is the formula for the alkanes?
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CnH2n+2
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What a single bonds known as?
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saturated compounds
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Aromatic hydrocarbons form what structure?
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rings
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aliphatic hydrocarbons include what compounds?
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alkanes and cyclic compounds that are non-aromatic
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What are the alkenes?
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have double bounds, so they're unsaturdated. therefore their H/C ratio is less than the Alkanes
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What is an isomer? why do we need to know about isomers?
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it's the same chemical formula, but a different structure. they have different properties, so they have different commercial purposes
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what are the cycloalkanes?
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looped compounds that are fully saturated. also known as napthanes
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What kind of bonds are in alkenes?
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single bonds
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what kind of bonds are the alkynes?
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single triple bond
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what kind of bonds do the alkadienes have?
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two double bonds
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What is petroleum derived from?
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the breakdown of organic matter
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what makes oil or gas sour?
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sulfur
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how is petroleum described?
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gravity (API and density) and GOR (gas to oil ratio)
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What are some methods for examining source rocks/oil/gas?
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pyrolysis, TOC analysis, gas chromatography, elemental composition, and vitrinite reflectance
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What is the distribution of an immature source rock, and why?
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it's a bimodal whale-back pattern because there is a high proportion of unsolved compounds
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what is the distribution of a mature source rock?
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a single peak because there are less unsolved compounds
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what do degraded oils show in their distribution?
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no peaks
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what are biomarkers?
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specific organic compounds that are uniquely reflective of a specific origin
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What do we need for a source rock?
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a high concentration of organic carbon
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What is the percentage of TOC for a great source rock?
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4% is good, 10-15% is excellent
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What is the majority of crustal carbon locked up in? and how much?
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82% in limestones and dolomites. 18% in coal, oil, and gas
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What are the types of sedimentary organic matter?
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kerogen and bitumen
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What is kerogen, and what percentage does it make up of sedimentary organic matter?
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90-95% mix of organic chemical compounds that are insoluble b/c of their huge molecular weight. may be thermally cracked during diagenesis to produce hydrocarbons
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What percentage of the sedimentary organic matter does bitumen make up? what is it?
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0-5%. it's a mix of organic liquids that are highly viscous, black, sticky, and entirely soluble in carbon disulfide. primparily highly condensed polycyclic aromatic hydrocarbons
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High initial hydrogen and low initial oxygen leads to...
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more petroleum generation and less CO2
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What is type I kerogen?
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mainly freshwater algae, cyanobacteria, and land plant resisn. it produces hydrocarbons easily and readily. mainly form in lakes. H/C ratio>1.25, O/C ratio<0.15
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What is type II kerogen?
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H/C ratio<1.25, O/C ratio0.03-0.18 produces oil and gas. deposited under reducing conditions
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What is type IIs kerogen?
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sulfur bearing
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What is type III kerogen?
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H/C ratio<1, O/C ratio 0.03-0.3. resembles coal and gas (some oil) very low hydrogen b/c extensive cycloalkanes. least attractive type of oil. forms from terrestrial plant matter.
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What do we want in the H:C ratio?
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a higher ratio. the higher, the better
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What kind of environment is type I kerogen deposited in?
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hydrogen rich, algal-lacustrine
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what kind of environment is type II kerogen deposited in? what about IIs?
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II deposited in hydrogen rich, marine. IIs= hydrogen and sulfur rich reducing marine conditions
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What kind of environment is type III kerogen deposited in?
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oxygen rich, hydrogen poor, terrestrial margin marine
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What is maceral?
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solid, organic substance, non-crystalline, naturally occuring, distinctive physically, no definite chemical composition. common component of kerogen
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What are the types of maceral groups?
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alginite (hydrogen rich, oil prone, type I), exinite (hydrogen rich, oil/gas prone), and vitrinite (oxygen rich, gas prone)
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What are the common macerals described in coal petrology in increasing maturity order?
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peat, lignite, bituminous, anthracite, and graphite
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What is the vitrinite reflectance?
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reflectance which indicates maturity. correlates to temp, pressure and time. higher it is, means higher depths or higher geothermal gradient
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what is catagenesis?
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the zone where oil and gas is generated
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what is dry gas also known as?
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thermogenic methane
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What is the problem with biogenic gas that's in the shallow subsurface?
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we see the reflection in seismic, and we know how much is there, but it's so dispersed that it is hard to produce
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What is zone 1 for hydrocarbon generation and expulsion?
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biochemical methane generation
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What is zone 2?
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initial thermochemical generation, no effective oil release, dry gas, wet gas, condensates, immature oil
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what is zone 3?
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main phase of mature oil generation and release. oil and gas window
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what is zone 4?
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thermal degradation of oil-phase hydrocarbons. into condensate, wet gas and dry gas
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what is zone 5?
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intense organic metamorphism
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What is hydrocarbon type a function of?
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geothermal gradient and depth
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what temperatures is the oil window between?
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65-150C
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What is the critical point?
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where oil and gas is produced
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What are the controls on oil composition?
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source rock type, thermal maturity, and oil attenuation
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What are factors that lead to a good source rock?
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high TOC, kerogen type (low oxygen index, high OI ok for gas) burial history, high PI and maturity
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How is a low oxygen EOD conducive to source rocks?
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it promotes the preservation of organic matter. this is enhanced in stagnant environments (protected or stratified waters are less mixed ie lakes)
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how is the rate of deposition conducive to source rocks?
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optimum rates of deposition promote higher proportion of organic matter vs. detrital or chemical sed. must be slow enough to prevent dilution and fast enough to prevent oxidation at sed. water interface. Need a perfect sedimentation rate
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How is a high abundance of organic matter conducive to a source rock?
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need organic material for hydrocarbons. high productivity and high hydrogen component (phytoplankton)
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What are the controls on productivity?
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bathymetry, climate, upwelling, thermohaline circulation, continental runoff, salinity, and light intensity
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what are the controls on organic preservation?
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oxygen content, sedimentation rate, and availability of chemical oxidizers
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Are volcanic sediments bad for reservoirs? examples?
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yes, ie western coast of south america
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Where and how do anoxic environments occur?
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density stratification that may result from thermal differences (like lakes) or salinity differences can create anoxia
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What are some major source periods?
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greenhouse times. neogene, mid-cretaceous, late jurassic, permian, devonian, and silurian
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During what sea level sequence do source rocks typically occur?
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transgressions and when there is rapid creation of oceanic crust
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What kind of basins formed in the triassic and jurassic?
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elongate rift basins. had source rocks and sealing salt
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When were some very anoxic ocean time periods?
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the mesozoic in general, but specifically the cretaceous
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do collisional margins produce good source rocks?
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yes because they form elongate basins
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Ice house conditions have what kind of oceans?
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oxygenated due to vigorous circulation
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greenhouse conditions have what kind of oceans?
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anoxic because there is sluggish circulation
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What are the types of petroleum systems?
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generative subsystem and migration-entrapment subsystem
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What are the charge factor types in a generative subsystem?
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supercharged, normally charged, and undercharged
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What are the types of migration-drainage styles in a migration-entrapment subsystem?
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vertically drained and laterally drained
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What are the entrapment styles in a migration-entrapment subsystem?
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high impedance and low impedance
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What to we need to know to estimate the charge factor?
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how rich the system is and how extensive are the source rocks and has oil been generated. Source potential index and maturity
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What is required to have a source rock?
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time and temperature.
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What do geohistory curves give us? what do we need to calculate this?
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the give us the point in time (and depth) for a potential source rock that was in the oil and gas window. need geothermal gradient
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What do we need to know to estimate migration?
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the structure and style, and basin geometry, existence and orientation of carrier beds and/or carrier faults (potentiometric lines or surfaces and focused or dispersive pathways), and the effectiveness of carrier beds (ie the efficiency and porosity and permeability)
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What is lateral migration?
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where hydrocarbons migrate laterally into age-equivalent reservoirs
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What is a potentiometric map? what is it effected by?
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it's a map of the fluid pressures that are allowing fluids to flow. it's affected by temp and pressure
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What does velocity do when it encounters kerogen? why?
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it slows because kerogen is waxy
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What is the main thing we need for migration to happen?
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layers that allow lateral migration and faults to allow vertical migration (unless they are sealing faults)
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What do migration pathways follow?
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structural contours and pressure gradients
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Focused drainage flows...
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low towards high, (anticline)
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dispersed drainage flows...
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low to high, away for low area. radiates out (synclinal)
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What are some barriers for fluid flow?
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seals, local pressure barriers, faults (fluid pathways are complex)
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To estimate the entrapment style, what do we need?
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structural style and basin geometry, and thickness and effectiveness of sealing rocks/faults (ie are the seals leaky? are seals broken by faults?)
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What is a high impedance trap?
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tight impermeable seals. like anhydrite, thick clay or thick organic rich shales
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What are some low impedance traps?
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weak seals that have been fractured, or they are leaky, or silt or sand bearing shales
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What are the types of carriers for fluids?
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permeable beds (can have low perm if time is long enough), permeable faults (as opposed to sealing faults), piercement structures (salt domes), and unconformitites
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What are some typical properties of juvenile basins?
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rapid accumulation, dominant compaction driven flow. Flow mostly upward and out of the basin. Minor elevation head flow near margins into the basin. Hard geopressure in thick shales
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What are some typical properties of a mature basin?
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slow accumulation, marginal uplift, dominant elevation head flow into basin with an upwelling flow in the basin center. minor compaction-driven flow
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What are some typical properties of a stagnant basin?
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no accumulation or erosion, low topographic relief, minor water driven flow by secondary consolidation
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What is a disassociated source? example?
|
where the reservoir is significantly different in age than the source interval. tar sands are a good example of this
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What is a associated source?
|
where the reservoir and source are essentially the same age
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why do we have to worry about alteration and biodegradation in a petroleum system?
|
geothermal cracking (deeper) or biodegradation (shallow) can alter oil chemisty. water washing can also degrade oil
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What are some observations we can make about fluid flow and geopressure?
|
water flows in sedimentary basins, petroleum migrates through many sed. basins, and rocks are buried and may be exhumed (which we tell us about pore volume and elevation change)
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All crustal rocks must have what?
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a solid framework and porosity
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In regard to pore space, are they allowed to be filled with nothing?
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no, pores have to be filled with a fluid. no vacuums allowed on Earth naturally
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what are typical fluids of pores?
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water, gas, oil, liquid CO2, or melt (magma or sulfur)
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What is the most dominant fluid in the subsurface?
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water
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What are the most common origins of subsurface water?
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depositional water (trapped in sed), meteoric recharge (aquifers), evaporitic (evaporite deposition makes highly saline brines), salt dissolution (dissolution of halite)
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What are the less significant origins of subsurface water?
|
brines caused by subsurface boiling near intrusions, reverse osmosis in geopressure zones, methane hydrate melting, and dehydration reactions
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What is the main reservoir driving mechanism?
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water drive (gravity drainage).
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How does gravity drive work?
|
there's an infinite supply of water because the reservoir is linked with a surface reservoir. these make the best reservoir recovery, but water production increases with time
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whre in the well is pressure the greatest?
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at the base of the well. fluid pressure decreases with decreasing depth
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What is needed for fluids to move?
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a change in pressure or pressure head
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What happens with a greater difference in head?
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fluid has a greater ability to flow
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what does fluid potential equal?
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head x gravity or (gravity)x(location elevation {z})+(P/density)
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What is the flow rate proportional to?
|
the fluid potential difference divided by the distance between fluid potentials. this gives us the potential gradient
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what does the term hydrodynamic mean?
|
that there are fluid potential differences and fluids will flow
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Is the density of a mineral the same as the density of the rock that mineral makes up? why?
|
no, because we have to take into account pores and fluids within pores. this produces a slightly lower than the density of the mineral
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What is the vertical max stress?
|
the weight of the overburden
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what is key in fracturing a rock?
|
the bulk shear modulus
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what's is a liquid's stress?
|
the pore pressure (measured in force)
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What is the average hydrostatic pressure?
|
0.465 psi/ft
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what is the average lithostatic pressure?
|
1.0 psi/ft
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how do we calculate mudweight using pressure?
|
P=0.052 x wt x D
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What do hydrostatic pressure, lithostatic pressure, and mudweight all have in common?
|
they are all temperature dependent
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why is stress different from pressure?
|
sed rocks are a porous media with connected pores. under static conditions, water pressure is transfered through the pores as if the rock weren't there. Rock weight is carried by grain to grain contacts, whereas water pushes back against the rock load equally from all directions. So processes effecting stress at grain contacts decreases with greater pressure. This is known as effective stress, where this is equivalent to the difference between a principle stress and pore pressure
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what is compaction disequilibrium?
|
where permeability is low and accumulation is high. water cannot escape as fast as the load is applied. Rock contacts don't adjust to overburden and the water supports part of the sediment weight. the water pressure exceeds hydrostatic pressure. leading to hard overpressure.
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pressure is equal to...
|
density x gravity x head
(rho)gh |
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Are grain densities heavier than bulk density? what does this mean?
|
yes! when using calculations, never use grain densities. only use bulk density!
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how do we calculate vertical stress?
|
take the average bulk density (lithostatic load) x the rock column height
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What does geopressure require?
|
heavier drilling fluids, casing points
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What can geopressure indicate?
|
that there's more gas per unit volume (greater profit)
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what can geopressure affect?
|
migration and trapping condictions (good if it aids, bad if the trap leaks)
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What can happen if mudweight is too low?
|
the well can blowout because there's uncontrolled fluid in the borehole
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what happens if mudweight is too high?
|
mud damages the formation, mud pressure exceeds minimum stress so the mud fractures into the formation. Mud is then lost and the well can blowout.
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When is casing set?
|
at pressure gradients
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What limits the max possible trapped petroleum column?
|
pore pressure
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When is trapping impossible?
|
no trap or when pore pressure is near the minimum stress. the source is expelled here and hydrocarbons migrate through fractures created by high pore pressure
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when will hydrocarbons migrate through tight seals?
|
when pore pressure is near minimum stress
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What are pressure cells? what causes it?
|
volumes of rock with a hydrostatic gradient surrounded by rock with higher pressure. This is caused by high permeability rock surrounded by low permeability rock
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Do seals need to be thick? why?
|
yes because thin beds are easier to fracture
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|
What is the best kind of map to see pressure gradients and predict flow paths?
|
potentiometric surface mapping
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|
does fluid flow from low pressure to high pressure?
|
no, it flows from high to low
|
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|
how do hydrocarbons migrate?
|
capillary pressure (capillary curves), buoyance, and multiple phases of fluid flow
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|
What is surface tension?
|
the energy per unit area created of a certain phase's surface creating molecular disorder near its edge
|
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What is surface energy equal?
|
surface tension x surface area
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what is surface tension affected by?
|
temperature, pressure, and compositional differences between phases
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do all phase boundaries have surface tension?
|
yes
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|
What is capillary pressure?
|
the pressure difference between two fluid phases in contact with one another at the same elevation. It is the force that resists the flattening of 'drops' so they retain their shapes.
|
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|
As pore throat diameter decreases, what happens to capillary pressure?
|
it increases
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|
What is wettability?
|
the surface tension between a rock sruface and two or more fluids. typically rocks are oil-wet or water-wet
|
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|
What determines if a reservoir is oil wet? is this common?
|
not common. it happens when water has a hard time displacing oil
|
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what determines if a reservoir is water wet? is this common?
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more common. it occurs when water easily displaces oil. This is better for production, but we also produce more water..
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what makes oil in pores resist traveling through pore throats?
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capillary pressure
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What controls the size and shape of the non-wetting fluid bubbles
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pore shape and size
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what is the main controls (besides pressure) on a fluids ability to flow?
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pore throats
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When will a non-wetting fluid invade a pore?
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when the capillary pressure is high enough to decrease the interference curvature to a radius less than that of a pore throat
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When does the volume of the non-wetting fluid increase?
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when capillary pressure increases
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What does the capillary pressure curve show?
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the measure of accessible pore-throat-size distribution, not pore-size distribution
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what is the capillary pressure curve a measure of?
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the non-wetting saturation as a function of capillary pressure. shape depends on fluids and saturation history. (can have multiple curves)
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What is the injection or drainage curve?
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where the non-wetting phase increases during measurement. all of the non-wetting phase forms a connected network
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What is a withdrawal or imbibition curve?
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where the non-wetting phase decreases during measurement. non-wetting phase snaps off, leaving a residual saturation
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What do surfactants do?
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they reduce tension by changing the wetting relationships and enhance recovery of the hydrocarbons
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what is relative permeability a function of?
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saturation and saturation history
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What is drainage?
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injection, wetting fluids drain from the rock as the non-wetting fluid enters
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what is imbibition?
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withdrawal, the wetting fluid spontaneously enters the rock and pushes the non-wetting fluid out
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If shale is fractured, what happens to capillary pressure?
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it decreases
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Is the pressure gradient of oil different than water? why?
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yes because oil is less dense than water
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Is bottom hole temperature on the log always accurate? why?
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no, because BHT is recorded by drilling fluids, which are at STP. If drilling fluids haven't been at bottom long enough, they won't record an accurate temp. we need fluids to be down there long enough to equilibrate and record an accurate temp.
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Why is temperature imporant in regard to drilling?
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because drilling tools are rated to certain temperatures, stability of mud changes with temp, maturity of rock, reservoir quality changes
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what is relative permeability a function of?
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saturation and saturation history
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What happens with lithic or arkosic reservoirs at high temperatures?
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they have lower porosity and permeability
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What is drainage?
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injection, wetting fluids drain from the rock as the non-wetting fluid enters
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What are the methods for heat transfer?
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radiant heat (infrared radiation through transparent media), advective heat transfer ( movement of heat with hot material), and conductive heat transfer (thermal diffusion through conductive material)
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what is imbibition?
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withdrawal, the wetting fluid spontaneously enters the rock and pushes the non-wetting fluid out
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Is the thermal gradient proportional to the thermal conductivity?
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no, it is inversely proportional. meaning when there is low conductivity, there's a steep thermal gradient. if there's high conductivity, there's a gentle thermal gradient
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If shale is fractured, what happens to capillary pressure?
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it decreases
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Is the pressure gradient of oil different than water? why?
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yes because oil is less dense than water
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Is bottom hole temperature on the log always accurate? why?
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no, because BHT is recorded by drilling fluids, which are at STP. If drilling fluids haven't been at bottom long enough, they won't record an accurate temp. we need fluids to be down there long enough to equilibrate and record an accurate temp.
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Why is temperature imporant in regard to drilling?
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because drilling tools are rated to certain temperatures, stability of mud changes with temp, maturity of rock, reservoir quality changes
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What happens with lithic or arkosic reservoirs at high temperatures?
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they have lower porosity and permeability
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What are the methods for heat transfer?
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radiant heat (infrared radiation through transparent media), advective heat transfer ( movement of heat with hot material), and conductive heat transfer (thermal diffusion through conductive material)
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Is the thermal gradient proportional to the thermal conductivity?
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no, it is inversely proportional. meaning when there is low conductivity, there's a steep thermal gradient. if there's high conductivity, there's a gentle thermal gradient
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what is thermal conductivity a function of?
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mineraology, porosity, and temperature
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As porosity decreases, what happens to conductivity, what does this result in?
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conductivity increases leading to a lower thermal gradient
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What are the main heat sources in Earth?
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basement origin (center of earth) and some heat from radioactive decay
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What is critical to understand the thermal history?
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understanding and knowledge of basin formation
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Where is heat flow lower? where is it higher?
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it's generally lower in older crust in the center of continents and higher in active margins
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what is a potential trap?
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it's untested or undrilled
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What are the components of a trap?
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trapping geometry, reservoir, seal, and charge
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What are the types of traps?
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structural, stratigraphic, hydrodynamic, and combination
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How do stratigraphic traps form?
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result from stratigraphic changes or diagenesis
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What is the most common trap drilled?
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anticline
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What is the closure?
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the last closed contour, so hydrocarbons cannot escape
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is a spill point the same as closure?
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no
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What do we need to make sure a trap is a true trap?
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a 3D map
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What determines the hydrocarbon type in a trap?
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the last hydrocarbon at the end of charging because no fractionation occurs in the trap unless it's filled to the spill point
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What is a spilling accumulation?
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where charge of hydrocarbons exceeds the trap volume without exceeding the seal capacity. hydrocarbons spill at the highest point below the seal and the petroleum-water-contact (PWC) is controlled by spill elevation. volume of the trap is fixed
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What is leaking accumulation?
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where there is sufficient charge so that capillary pressure exceeds the seal capacity but trap volume isn't filled to the spill. hydrocarbons leak where capillary pressure exceeds seal threshold pressure. The elevation of the PWC is controleld by the charge rate. the faster the charge, the higher the hydrocarbon column
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in leaking accumulation settings, if there is both oil and gas, what does the reservoir tend to be?
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more oil prone because the gas will leak first
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in a leaking accumulation, what ratio do we need for hydrocarbon accumulation?
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leak has to be less than charge
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what is a leaky and spilling accumulation?
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where there's sufficient charge so capillary pressure exceeds seal capacity and trap volume. the trap leaks and spills. if the seal capacity is strong, reservoir becomes more gas prone, if weak, more oil prone.
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what is fill and spill accumulation?
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wehre the hydrocarbons fill the trap to the spill point, and spill, moving updip.
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What is the closure?
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the last closed contour, so hydrocarbons cannot escape
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is a spill point the same as closure?
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no
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What is the closure?
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the last closed contour, so hydrocarbons cannot escape
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What do we need to make sure a trap is a true trap?
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a 3D map
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is a spill point the same as closure?
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no
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What determines the hydrocarbon type in a trap?
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the last hydrocarbon at the end of charging because no fractionation occurs in the trap unless it's filled to the spill point
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What do we need to make sure a trap is a true trap?
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a 3D map
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What is a spilling accumulation?
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where charge of hydrocarbons exceeds the trap volume without exceeding the seal capacity. hydrocarbons spill at the highest point below the seal and the petroleum-water-contact (PWC) is controlled by spill elevation. volume of the trap is fixed
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What determines the hydrocarbon type in a trap?
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the last hydrocarbon at the end of charging because no fractionation occurs in the trap unless it's filled to the spill point
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What is a spilling accumulation?
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where charge of hydrocarbons exceeds the trap volume without exceeding the seal capacity. hydrocarbons spill at the highest point below the seal and the petroleum-water-contact (PWC) is controlled by spill elevation. volume of the trap is fixed
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What is leaking accumulation?
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where there is sufficient charge so that capillary pressure exceeds the seal capacity but trap volume isn't filled to the spill. hydrocarbons leak where capillary pressure exceeds seal threshold pressure. The elevation of the PWC is controleld by the charge rate. the faster the charge, the higher the hydrocarbon column
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What is leaking accumulation?
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where there is sufficient charge so that capillary pressure exceeds the seal capacity but trap volume isn't filled to the spill. hydrocarbons leak where capillary pressure exceeds seal threshold pressure. The elevation of the PWC is controleld by the charge rate. the faster the charge, the higher the hydrocarbon column
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in leaking accumulation settings, if there is both oil and gas, what does the reservoir tend to be?
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more oil prone because the gas will leak first
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in leaking accumulation settings, if there is both oil and gas, what does the reservoir tend to be?
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more oil prone because the gas will leak first
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in a leaking accumulation, what ratio do we need for hydrocarbon accumulation?
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leak has to be less than charge
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what is a leaky and spilling accumulation?
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where there's sufficient charge so capillary pressure exceeds seal capacity and trap volume. the trap leaks and spills. if the seal capacity is strong, reservoir becomes more gas prone, if weak, more oil prone.
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in a leaking accumulation, what ratio do we need for hydrocarbon accumulation?
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leak has to be less than charge
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what is fill and spill accumulation?
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wehre the hydrocarbons fill the trap to the spill point, and spill, moving updip.
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what is a leaky and spilling accumulation?
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where there's sufficient charge so capillary pressure exceeds seal capacity and trap volume. the trap leaks and spills. if the seal capacity is strong, reservoir becomes more gas prone, if weak, more oil prone.
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what is fill and spill accumulation?
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wehre the hydrocarbons fill the trap to the spill point, and spill, moving updip.
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|
|
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what is thermal conductivity a function of?
|
mineraology, porosity, and temperature
|
|
|
|
As porosity decreases, what happens to conductivity, what does this result in?
|
conductivity increases leading to a lower thermal gradient
|
|
|
|
What are the main heat sources in Earth?
|
basement origin (center of earth) and some heat from radioactive decay
|
|
|
|
What is critical to understand the thermal history?
|
understanding and knowledge of basin formation
|
|
|
|
Where is heat flow lower? where is it higher?
|
it's generally lower in older crust in the center of continents and higher in active margins
|
|
|
|
what is a potential trap?
|
it's untested or undrilled
|
|
|
|
What are the components of a trap?
|
trapping geometry, reservoir, seal, and charge
|
|
|
|
What are the types of traps?
|
structural, stratigraphic, hydrodynamic, and combination
|
|
|
|
How do stratigraphic traps form?
|
result from stratigraphic changes or diagenesis
|
|
|
|
What is the most common trap drilled?
|
anticline
|
|
|
|
What is the closure?
|
the last closed contour, so hydrocarbons cannot escape
|
|
|
|
is a spill point the same as closure?
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no
|
|
|
|
What do we need to make sure a trap is a true trap?
|
a 3D map
|
|
|
|
What determines the hydrocarbon type in a trap?
|
the last hydrocarbon at the end of charging because no fractionation occurs in the trap unless it's filled to the spill point
|
|
|
|
What is a spilling accumulation?
|
where charge of hydrocarbons exceeds the trap volume without exceeding the seal capacity. hydrocarbons spill at the highest point below the seal and the petroleum-water-contact (PWC) is controlled by spill elevation. volume of the trap is fixed
|
|
|
|
What is leaking accumulation?
|
where there is sufficient charge so that capillary pressure exceeds the seal capacity but trap volume isn't filled to the spill. hydrocarbons leak where capillary pressure exceeds seal threshold pressure. The elevation of the PWC is controleld by the charge rate. the faster the charge, the higher the hydrocarbon column
|
|
|
|
in leaking accumulation settings, if there is both oil and gas, what does the reservoir tend to be?
|
more oil prone because the gas will leak first
|
|
|
|
in a leaking accumulation, what ratio do we need for hydrocarbon accumulation?
|
leak has to be less than charge
|
|
|
|
what is a leaky and spilling accumulation?
|
where there's sufficient charge so capillary pressure exceeds seal capacity and trap volume. the trap leaks and spills. if the seal capacity is strong, reservoir becomes more gas prone, if weak, more oil prone.
|
|
|
|
what is fill and spill accumulation?
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wehre the hydrocarbons fill the trap to the spill point, and spill, moving updip.
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what is a hydrodynamic tilted contact? why is this important?
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where the oil-water-contact tilts in the direction of fluid flow. this is important for volumetric calculations
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What is waste rock? what is it also known as?
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tight reservoir. rock in a trapping geometry with permeability to high to form a seal, but porosity and permeability are too low to form an economic reservoir (not really true today)
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Can reservoir quality change laterally?
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yes, lateral seals can form
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Does buoyancy need to be less than capillary pressure?
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yes, because the seal will not be effective if not
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What is a juxtaposition seal?
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where the reservoir lies below or adjacent to a shale or other sealing lithology
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What is a membrane seal?
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a low permeability fault zone preventing flow of hydrocarbons between adjacent reservoir facies. Sealing also has juxtaposition component
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What do fault seals depend on?
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fault rock type
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What is good quality in a fault sea?
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clay smears
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How do we find the clay smear factor?
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fault throw divided by bed thickness
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If the clay smear factor is less than 3 then...
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there are continuous clay smears
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if the clay smear factor is 3-10 then...
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clay smears are 60% discontinuous
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if the clay smear factor is greater than 10 then...
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the clay smears are 70% discontinuous
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What are the kinds of fault rock zones?
|
disaggregation zones (loose sed), cataclastic zones (def/m bands, breaking of rock by faulting, 5-15% clay), phyllosilicate framework fault zones (15-40% clay smears), clay smears (>40% clay), and cemented faults/fracutres (previour conduits of fluid flow)
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