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216 Cards in this Set
- Front
- Back
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Explusion of Hydrocarbons from source rock |
Primary Migration |
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The two types of evolution of Organic Matter in source rocks during burial |
1. Bacterial Decay: Organic Matter -> Methane
2. Increasing Temperature Organic Matter -> Kerogen -> Bitumen -> Oil + Gas + Residue |
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Kerogen Maturation and Hydrocarbon Generation Graph |
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How does Oil get out of the Source Rock?
Source rocks are _____ ______ with high total organic content (TOC)
Source rocks have very low permeability around ________ to ________ Darcy |
black shales
1 x 10^-9 to 1 x 10^-7 Darcy |
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What is the problem with expulsion during compaction? (Proposed Expulsion Mechanism) |
Wrong Timing
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What is the problem with the dissolution in water? (Proposed Expulsion Mechanism) |
Insufficient
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What is the problem with the natural detergents or micelles? (Proposed Expulsion Mechanism) |
Insufficient
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What is the problem with the dissolution in gas phase? (Proposed Expulsion Mechanism)
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Works for light oil, but not for heavy oil |
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Explain the Oil Phase Migration. (Proposed Expulsion Mechanism) |
Kerogen is 5-10% of source rocks and is load bearing.
Maturation transforms kerogen to a hydrocarbon fluid.
The fluid is also load-bearing, therefore overpressured.
Overpressure fractures the rock.
Hydrocarbons escape through microcracks.
Cracks close up until a new episode of generation takes place. |
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Hydrocarbon maturation creates ________ ________ that allows the oil and gas to escape the impermeable source rock. |
fracture porosity |
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Name four main characteristics of Primary Migration. |
High % TOC (Total Organic Content)
Kerogen to liquid transformation
Microfracturing
Expulsion |
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Secondary Migration consists of these 6 things. |
Driving Force Resisting Forces Phase Behavior Rates of Migration Efficiency Long Distance Migration |
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Secondary migration is driven by ________ and opposed by __________ _________. |
bouyancy
capillary pressure |
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Secondary Migration
Movement from source to ____.
Along _______ bed.
As separate hydrocarbon _____. (mostly) |
trap
carrier
phase |
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State the capillary pressure equation. |
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Mercury pressure vs. Mercury saturation |
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The larger the column of oil, the higher the _______ force. |
bouyancy |
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Seals are not absolute. They depend on _____. |
forces |
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The smaller the pore space, the harder it is for oil to get through. |
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Displacement Pressure in Seal Rock |
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Because rocks are inhomogeneous , oil does not fill the entire reservoir. (The capillary sizes are different.) |
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The WOC and GOC are horizontal if hydrostatic. |
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___ can move through seals easier because it is more bouyant. |
Gas |
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Migration Pathways |
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Migration Pathways (up dip: perpendicular to contours) |
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Evidence for long distance migration |
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Term for when bacteria eat short-chain hydrocarbons |
biodegradation |
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Oil can move ______ miles from the source rock. |
hundreds of miles |
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Migration is relatively short when compared to the _____ ____. |
basin life |
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During migration there is a loss of some oil due to ________. |
wetting |
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____ sorting typically leads to low porosity and permeability. |
Poor |
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What is % of void space in rock? |
Porosity |
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What is ease of fluid flow? |
Permeability |
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Total porosity and Effective Porosity |
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View of Porosity 0-5% _____ 5-10% _____ 10-15% _____ 15-20% ______ 20-25% _____
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0-5% Negligible 5-10% Poor 10-15% Fair 15-20% Good 20-25% Very Good |
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For ___, lower porosity is still viable. |
gas |
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______________ makes low porosity less of a problem. |
Hydrofracturing |
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Name the five things that control primary porosity. |
1. Degree of Uniformity of Grain Size (Sorting) 2. Shape of the Grains 3. Method of Deposition (Manner of Packing) 4. Compaction 5. Cementation |
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Classify the sorting. |
Poor sorting |
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Classify the sorting. |
Intermediate sorting |
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Cubic packing has __% in the ideal situation. |
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Rhombohedral packing has __% porosity in the ideal situation. |
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Additional open space developed after sedimentation. |
Secondary porosity |
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Name 3 Sandstone modifications to porosity |
1. Pressure Solution 2. Cementation 3. Fracturing |
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Name 5 Carbonate modifications to porosity |
1. Compaction - 2 to 20% 2. Solution 3. Recrystalization - Dolomitization 4. Fracturing 5. Cementation
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Name 2 Shale modifications to porosity |
1. Compaction - 50% 2. Bound Water Expulsion |
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What does the % cement affect the porosity? |
More cement means less porosity. |
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Porosity in Sandstone |
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More fractures leads to more porosity. |
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________ Porosity |
Secondary Porosity |
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When limestone is exposed to water with Mg, some Ca are replaced by Mg. |
Dolomitization |
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Since dolomite is more compact than calcite, this leads to ___ ______. |
new porosity |
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Dolomitization |
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Shale |
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Large well connected pores are ______. |
permeable |
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Smaller, fewer or less interconnected pores are _________. |
impermeable |
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Darcy's Equation |
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Permeability Values 1-10md ____ 10-100md ____ 100-1000md ____ |
Permeability Values 1-10md Fair 10-100md Good 100-1000md Very Good |
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1 _____ permits a flow of 1cm3/s of fluid with viscosity 1cp under a pressure gradient of 1atm/cm acting across an area of 1cm2. |
darcy |
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Highest permeability to lowest |
Clean sand -> Silty sand -> Sandstone & Limestone -> Marine Clay -> Shale |
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Porosity can be measured by _____ and _____ logs. |
density and neutron logs |
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Permeability requires ____ for lab injection tests. |
cores |
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Log (permeability) vs. porosity is linear. |
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Flow changes with _______ saturation. |
multi-fluid |
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Relative Permeability |
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Petroleum exists in ___ _____. |
pore space |
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______ and _____ decrease porosity. |
compaction and cementation |
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_____, _____, and _____ increase porosity. |
Dissolution, fracturing and dolomitization |
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______ controls migration and production |
Permeability |
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Oil, gas and water _____ each other's flow. |
impede |
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_____ ______ are necessary to manage reservoirs effectively. |
Reservoir models |
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What makes a carbonate reservoir? |
1. porosity strongly controlled by post-depositional processes 2. high initial porosity 3. rapid cementation 4. dissolution creates secondary porosity (usually due to acidic water. |
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Carbonate Porosity Types |
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Intergranular Porosity |
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Vuggy and Moldic Porosity |
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Beach Systems |
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Dissolution by Meteoric Water |
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Karst and Unconformities |
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Persian Gulf Petroleum System |
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Arab D Reservoir - Ghawar |
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Daily Oil Production as of 2008 |
1. Russia 2. Saudi Arabia 3. USA 4. Iran 5.China |
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What is Dolomitization? |
When dolomite forms during diagenesis or hydrothermal alteration.
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Fractured Reservoirs |
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Evidence for fluid flow along Fractures in Sandstone. |
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Systematic Orthogonal Fractures |
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Fracture Spacing/Bedding |
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Sealed Fractures |
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Ooids |
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Intragranular porosity |
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Estimated Ultimate Recovery Map |
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Net Pay Isopach |
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Important things to know |
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Important things to know |
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Calcite filled vugs and fractures |
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Fault well production |
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What is very important in carbonate reservoirs? |
secondary porosity |
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What creates new porosity? |
dolomitization, dissolution, and fracturing |
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What does exposure to meteoric water lead to? |
limestone dissolution |
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What does natural fracture networks enhance? |
permeability |
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There is no way to control formation fluids and pressures with... |
a cable tool drilling rig |
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Cable Tool Drilling Rig |
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A rotary drilling rig consists of |
engines, hoist system, rotating system, mud system |
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Rotary Drilling |
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Traveling Block |
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The Rotary System |
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Tricone Bit |
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Drilling Rates |
-Sandstones are fast -Limestone/dolomite can be slow -Shales are slow |
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Mud System |
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Drilling Mud |
-Bentonite (clay) - 9-10 lb/gal -Barite (BaSO4) - 15-20 lb/gal |
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Casing |
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Coring Assembly and Core Bit |
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Types of offshore oil and gas structures |
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Horizontal Drilling Components |
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What is used downhole in deviation drilling? |
knuckles or swivel joints |
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What is the aim for directional control? |
The aim is to create the appropriate side force on the bit so that the resultant force drives the bit to the desired direction. |
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Drilling tools and methods |
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Drilling tools and methods |
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Logging-while Drilling tools |
-Directional Data (inclination, azimuth, tool-face) -Formation characteristics (gamma-ray, resistivity logs, etc) -Drilling parameters (down-hole WOB, torque, rpm) |
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Logging a horizontal well |
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Hydraulic fracturing in a wellbore |
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Where was the Macondo Well located? |
On a deepwater horizon rig off the coast of Alabama, Mississippi, and Louisiana in the Gulf of Mexico. |
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About how many active platforms are in the US Gulf? |
about 4000 |
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DeepWater Horizon Rig |
-owned and operated by Transocean -Contracted by BP and it partners (Anadarko, Mitsui) -state of the art vessel -dynamically positioned |
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Macondo Well Reservoir Properties |
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Problems Prior to Accident |
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Why did they prepare to temporarily abandon the well? |
-long string casing -nitrogen foam cement job by Halliburton -cement test by Halliburton showed 48 hours needed for cement to set at 180 F. -April 18- Casing installed with only 6 centralizers (instead of 21) -Had trouble with bottoms-up circulation |
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The Blow Out - April 20 |
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The Blow Out |
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Aftermath |
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Efforts to stop the leak |
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Blow Out Preventer |
-Shear ram blocked by buckled pipe -Miss wiring and battery failure in the emergency system |
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(Maconda Well) Small errors can |
add up |
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(Maconda Well) Economic pressures and safety are in a |
natural conflict |
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(Maconda Well) "Getting the job done" sometimes leads you to a |
bad outcome |
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The Logging Operation |
-100 and 200 feet repeat section measured at the bottom -then tool is raised through the entire well -casing may prevent some logs from working -logging speed: 1800 to 3600 ft/hour -information pertinent to both the logging run and the well is recorded on the header -logs recorded digitally |
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Log Types |
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Spontaneous Potential (SP) |
-one of the oldest logging measurements (used commercially in 1931) -discovered as noise in resistivity -found to be related to presence of sandstone |
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The well works like a battery |
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SP (Spontaneous Potential) |
has poor limestone response |
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Gamma Ray Log |
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Spectral Gamma Ray |
distinguishes the different sources of gamma rays |
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The Borehole Environment |
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Resistivity |
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What are the 3 classes of resistivity tools |
-electrode logs -laterologs (focused electrodes) -induction |
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The normal resistivity tool spacing of electrodes determines |
penetration |
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The guard or laterolog electrodes focus |
the current in a narrow disk |
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(Induction) Receiver coil measures |
the induced electrical field created in the rocks by the transmitter coil |
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ID (deep induction), IM (medium induction), and LL8 (shallow induction) measures |
resistivity at different distances form the borehole |
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Calculating Fluid Saturation |
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Sonic (Acoustic) Logs |
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Sonic (Acoustic) Logs |
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Which unit is the best reservoir? |
low shale and high porosity |
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Creating synthetic seismic data |
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Density Log |
-measures of density -tied to lithology, porosity, and fluid content -tool emits gamma rays -detects returning scattered gamma rays -gamma ray absorption is proportional to rock density |
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Porosity Calculation |
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Neutron Log (CNL) |
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If lithology is known... |
neutron and density logs can be calibrated for porosity |
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Gamma Ray Response to Grain Size |
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Relating log character to sedimentary facies |
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Steps of building a reservoir model |
1. define facies in core 2. relate facies to log 3. predict facies in wells without core, but with good logs. |
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Log Datum Terminology |
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Mud pulse telemetry |
pressure pulses |
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electromagnetic telemetry |
using conductivity of drill pipe |
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wired drill pipe |
The future. Faster and better, but delicate. |
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Dipmeter |
vertical dip variation is characteristic of the structure |
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Well logs provide |
key data for understanding the subsurface |
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Lithology, porosity and fluids are |
3 important log families |
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Usually you can't measure these properties directly, so you must use |
proxies or indirect measurements |
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Multiple logs used in combination are |
most powerful |
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Label |
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_____ _____ is the process by which hydrocarbons are expelled from the source rock into an adjacent permeable carrier bed. |
Primary migration |
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Solution: The solubility of hydrocarbons is water is very low, usually less than 50 ppm. Exceptions are methane, benzene and toulene which may have solubilities of 500 to 2000 ppm at reservoir conditions. Solubility is enhanced by increasing temperature, but within the oil window temperatures are too low to make any difference. In summary, the volumes of water required to move the hydrocarbons found in a normal oil field would huge due to the low solubility. So this is not an important mechanism for primary migration. |
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_____ are molecules that behave like soap, attaching themselves to a hydrocarbon molecule on one end and to an OH- at the other end. These could increase the amount of hydrocarbons transported by water. However, micelles are not found in rocks in sufficiently large quantities to explain most hydrocarbon accumulations. |
Micelles |
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_______ of most hydrocarbons through rocks is also exceedingly slow. Methane can diffuse through shales, but very slowly. This helps to explain why small quantities of methane can be detected in many sedimentary rocks, but cannot explain the formation of any significant gas deposit. Molecules larger than butane are to big to move by diffusion at all. |
Diffusion |
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Gas phase migration- Compressed gas can dissolve liquid hydrocarbons. For example at 5000 psi (conditions found at about 10,000 feet) methane and decane (C1 and C10) form a single gas phase. Migration of hydrocarbons dissolved in the gas phase can facilitate the movement of hydrocarbons through the source rock, as the gas phase migrates into shallower regions where temperature is lower, the liquid hydrocarbons come out of solution. However, the gas/oil ratio of most oil fields is too low for the gas to be the only means of transporting the oil out of the source rock. Also at the onset of generation most the kerogen produces little gas, most gas is generated late during the maturation history. |
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Oil Phase Migration- Most hydrocarbons probably are expelled from the source rock as liquids. The expulsion of the oil out of the source rock is a dynamic process driven by the oil generation itself. Good source rocks have TOC (total organic content) ranging from 3 to 10%. At low TOC the kerogen may occupy a position within the matrix porosity of the rock, at high TOC the kerogen can form connected bands within the rock. Then the kerogen is bearing part of the lithostatic load. As he organic matter transforms into oil this load-bearing kerogen turns into liquid. The fluid pressure of the oil within the black shales can become high enough to produce microfractures in the rock. Once the microfractures form, the oil is squeezed out and the source rock collapses. So primary migration can be viewed as a second episode of compaction. Microfractures of this type can be seen in most productive source rocks and they are often filled with remnants of oil. |
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In order for expulsion to take place a minimum level of saturation of the source rock with oil must be reached. This minimum level depends on the viscosity ratio between the oil and the water. Low viscosity oils can be expelled at low saturation (less than 10%), high viscosity oils require saturations larger than 50%. This means that the efficiency of generation is greater for low viscosity (high API) oil than for high viscosity (low API). |
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______ _____ is the movement of hydrocarbons along a "carrier bed" from the source area to the trap. Migration mostly takes place as one or more separate hydrocarbons phases (gas or liquid depending on pressure and temperature conditions). There is also minor dissolution in water of methane and short chain hydrocarbons. |
Secondary migration |
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Driving forces for migration: * _______ (This force acts vertically and is proportional to the density difference between water and the hydrocarbon so it is stronger for gas than heavier oil)* ______ ____ (water potential deflect the direction of oil migration, the effect is usually minor except in over pressured zones (primary migration)) |
Buoyancy
Hydrodynamic flow |
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Resisting forces: * _____ ____ (opposes movement of fluid from coarse-grain to fine- grain rock, also the capillary pressure of the water in the reservoir resists the movement of oil) |
Capillary pressure |
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One result of hydrodynamic flow is a tilted oil-water contact (OWC) in a trap. OWC is an equipotential surface, but if the water is flowing the equipotential surfaces are inclined in the direction of flow, so the OWC will be tilted too. |
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During migration the pressure and temperature conditions of the hydrocarbons can change a lot affecting the _____ _______ of the oil. |
phase behavior |
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Example 1: Type I, oil prone source rock during peak generation produces oil with a gas-oil ratio (GOR) of 0.2 kg/kg (1000 cf/bbl). At depths greater than ~10,000 ft all the gas can be dissolved in the oil.Migration will be as a single liquid hydrocarbon phase. Above ~10,000 ft the gas will begin to exsolve, like opening a soda can. At that point two hydrocarbon phases will migrate together. |
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Example 2: A gas-prone source rock produces a gas condensate with high proportion of dissolved liquid C6+ hydrocarbons. As pressure and temperature drop the C6+ fraction will condensate as a minority liquid phase. |
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___ __ ______ is controlled by Darcy's law q= -k/v dp/dz (for a single fluid phase) where q=volumetric flow rate, k=permeability, v=viscosity, dp/dz=pressure gradient. Given typical permeabilities of sandstone, and flow rate of oil can range from 1 to 1000 km per million years. This is faster than rate of generation and expulsion, so oil generation is the rate-limiting factor. |
Rate of migration |
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Because the carrier bed has to reach a minimum oil saturation before oil can flow, there is a volumetric loss associated with migration. The oil will seek a tortuous path of least resistance which typically will be a small portion of the total carrier bed volume. |
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Very long horizontal migration distances have been documented in some basins, in the Alberta basin of Canada the oil has migrated more than 400 km. In other cases the dominant direction of migration is vertical following fault or fracture systems, such as some accumulation in the North Sea.
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What is good porosity? 0-5% - Negligible 5-10%- Poor 10-15%- Fair 15-20%- Good >20% - Very good |
Practical cut off for oil
Sandstone ~8% Limestone ~5% For gas the cut off is lower |
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This microphotographs illustrates the typical components of a sandstone reservoir: quartz grains (gray), secondary quartz cement (also gray), pore space (dark), and secondary minerals in the pore spaces (brownish). Notice that the original grains are well rounded, but the quartz cement is forming a polygonal crystal. |
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This is an example of well-rounded, clean sandstone. The green area is open pore space. This rock has high porosity and probably high permeability also. |
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Poorly sorted coarse sandstone. The spaces between the large, well-rounded grains are filled by small angular fragments in a dark clay-rich matrix. This rock has very low porosity and permeability. |
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This is a sandstone that has been completely cemented. It is now a quartzite: a metamorphic rock with no porosity left. Notice that irregular grain boundaries, like a jig-saw puzzle.This is the result of pressure solution under high stress conditions. Pressure solution causes the grains to indent each other at the points of contact. |
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This is an oolitic sandstone with most of the primary porosity (space between the round oolites) filled with secondary quartz crystals. |
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This is the key parameter in determining reservoir quality. Many rocks (shales for example) have high porosity, but very low permeability. Determined from Darcy's law. |
Permeability |
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Main controls on permeability are:
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Grain size (determines the size of the pore throats) Pore connectivity |
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When multiple fluids are present they interfere with each other. So that the effective permeability of the moving fluid is much lower than if a single fluid is present. In a typical reservoir at least water and oil are present, frequently water, oil, and gas share the pore space. |
Effective permeability |
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What is good permeability?
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<1 millidarcy - Poor 1-10 md- Fair 10-100 md- Good 100-1000 md- Very good |
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Processes that reduce porosity and permeability: |
Compaction Cementation Heavy hydrocarbon residue |
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Processes that enhance porosity and permeability: |
Dissolution Fracturing Dolomitization |
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____ ___ are often subjected to early cementation, so reservoir quality depends very strongly on dissolution, fracturing and dolomitization. Most carbonate reservoirs are due to secondary porosity. Reefs sometimes preserve primary porosity. |
Carbonate rocks |
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total thickness of the reservoir unit |
Gross pay |
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the fraction of the reservoir that has porosity above a minimum threshold (this is the sum of the productive zones) |
Net pay |
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Reservoir barriers
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Reservoirs are heterogeneous in both vertical and horizontal dimension at all scales. This is due to Stratigraphic facies changes, faults, variation in diagenetic features such as cementation or dissolution, etc. A huge body of data is needed to adequately characterize most reservoirs. Most often reservoir barriers are revealed by the pressure history of neighboring wells. |
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A modern rotary drill rig is composed of four separate systems: Engines-Power everything Hoist syst.-Used to lift, lower and suspend the drill string in the well Rotating syst.- Mud System |
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The rotating system consists of the kelly, rotary table, the drill string, the drill collars and the bit. |
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The mud system is used to pump drilling mud down the drill string and back up to the surface. This system has multiple functions: Control the subsurface pressure via Mud weight Blow-out preventers (valves) Prevent the hole from collapsing Cool the drill bit Remove the drill cuttings
Drilling mud is a key element of the drilling process. If the mud weight is too high the reservoir may be damaged, if too low there may be a blow out if a high pressure zone is encountered.
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Steel casing (heavy gage pipe) is used to maintain the integrity of the hole and to isolate specific strata.
Surface casing is always set in order to attach the blow-out preventers to control pressure. If the well is successful, production casing is lowered to the reservoir, cemented to the walls and perforated in front of the reservoir unit in order to be able to test and produce that interval.
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In some cases it is necessary to set an intermediate casing in order to isolate an over pressured (or under pressured) layer. Otherwise it would be necessary to maintain excessively high mud weight that would invade the reservoir damaging it. |
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Wells are not always vertical. If the beds are tilted the well will tend to "walk" up-dip causing the well to deviate. In other cases the well is deviated on purpose, such as in order to drill several wells from a single surface location, or if it necessary to "side-track" the hole to avoid an obstruction. Directional drilling is done with a bit that is powered by a down hole motor (or turbine) instead of powered by turning the entire drill string from the surface. |
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During drilling well side geologists monitor many parameters that help figure out the stratigraphy that is being drilled, as well as detect any hydrocarbons that may be present. Log of the well cuttings Log of gas and gas chromatography Oil shows Drilling rate Mud weight Any kicks (high pressure zones) |
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Drilling rate depends on lithology. |
Sandstones are fast to drill, shales are more difficult as well as carbonates. |
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Cores can be used to sample any unit of interest. Sidewall cores are collected by lowering a tool that has hollow sampling bullets attached with a wire. Small cylindrical plugs are recovered when the tool is pulled back out. Conventional cores are cut with a bit that cuts a cylinder of rock and traps it inside the drill string. |
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Drill-stem-tests (DST): It is possible to test the fluids in an open hole by setting packers above and below the interval of interest. This way a unit is isolated and the formation fluids are allowed to flow into the drill string. This way the formation pressure, and permeability can be measured and the formation fluids sampled. DST's are often unreliable because it is difficult to completely isolate the reservoir unit. Also frequently some of the drilling mud has invaded the formation, so pristine fluids do not flow into the well. |
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The table on the left summarizes the main types of logs and their uses. The principal uses of well logs are: Lithologic determinations Stratigraphic correlations Evaluation of formation fluids Porosity determination Correlation with seismic data Location of faults and fractures Determination of the dip of strata |
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This is an example of the use of the Gamma ray (GR), SP, Resistivity (Rsn, Ril), Neutron (CNL), and Density (FDC) logs to identify a gas-rich zone. The Gamma Ray and SP indicate the location of the reservoir bed, the high Resistivity at the top of the bed shows that it is saturated with hydrocarbons, the cross-over of the Neutron and Density logs shows that the hydrocarbon in question is gas. |
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