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147 Cards in this Set
- Front
- Back
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What are the three limitations of well log data?
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Indirect measurements
Vertical Resolution Depth of Investigation |
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What are the open hole logging tools?
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Passive Track:
Caliper Gamma Ray Spontaneous Potential Active: Acoustic Nuclear |
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What are the cased hole logging tool types?
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Passive:
Gamma Ray Temperature Flow Velocity Caliper Active: Acoustic Nuclear Electromagnetic Mechanical |
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What is the difference between memorized logs and unmemorized logs?
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Memorized logs move all the logs to the same depth. Unmemorized logs don't have a depth shift.
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Oil based muds have what kind properties?
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Low conductivity, shallow invasion, and thin mud cake
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Water based muds have what kind of porperties?
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Moderate to very conductive
Shallow to deep invasion Thin to thick cake |
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What do you use caliper logs for?
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Hole volume
Mudcake (and indirectly permeability) Tool Corrections Crude lithology indicator |
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How are electrical potentionals created (for SP log)?
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Potentials are created by chemically induced electric current.
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What are SP logs used for?
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Values of water resistivity
Identify permeable zones Qualitative indication of shale content define bed boundaries well to well correlation |
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What kind of mud do you need for SP log?
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Water based mud
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What are the three effects (two main one minor) of SP?
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Liquid Junction Potential (Major)
Membrane Effect (Major) Electrokinetic (Minor) |
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What factors affect SP response?
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HC-reduce
Shale-reduce Bed thickness - need thick bed to develope SP deflection Perm - low perm cause high invasion dia. Messes with junction potential. |
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What are gamma ray logs used for?
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Correlation
Lithology indicator Mineral ID Evaluation of shale content fracture detection |
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What is the difference between spectral gamma ray and gamma ray?
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Spectral records the source of the radioactivity
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What are the three main contributors to natural Gamma Ray?
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Potassium 40
Thorium 232 Uranium 238 |
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What are the common gamma ray corrections?
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Hole size
mud density tool position in hole casing diameter casing size and weight cement thickness |
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What is the definition of Vshale?
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matrix volume (silt and dry clay) + fluid (bound water)
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What type of spectral GR analysis shows fractures?
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High uranium content
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What are the the three porosity tools?
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Sonic (acoustic)
Density Neutron |
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What are the applications of Sonic logs?
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Determine porosity and lithology
Determine Rwa Determine formation mechanical properties Evaluate fractures and permeability Evaluate overpressure in basin Evaluate cement bonds |
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How do sonic logs operate?
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It generates a sound that is recorded.
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How fast do P waves travel?
What do P waves travel through? |
They travel through mud and rock
In mud they travel 5,200 ft/sec in rock they travel 18,000-25,000 ft/sec. They travel the fastest out of the different waves (Compresional wave) |
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What do S waves travel through?
How fast do S Waves travel? What type of wave is an S wave? Are they sensitive to anything? |
Travel through rock at 11,000-14,000 ft/sec
It's a shear wave. It is fracture and shale sensitive. |
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What do Stoneley waves travel through?
How fast do Stoneley Waves travel? Are they sensitive to anything? |
They travel through mud and rock
It's the slowest wave traveling 3,300 to 5,000 ft/sec. It is sensitive to fracture and permeability |
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What are two causes of bad sonic logs?
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Road Noise
Cycle Skipping |
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What is road noise?
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Road noise is caused by tool movement along the borehole generating a high frequency noise component that is superimposed onto the normal acoustic signal.
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What are cycle skips?
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A skip in the cycle. It occurs when only one of a pair of recievers is triggered by an arriving wave, which causes sharp deflections on the log.
It is caused by gas in the mud, washouts, or if the threshold level is set too low |
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What is sonic porosity primary affected by? Secondarily?
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Primary
Lithology Porosity Secondarily Fulids Compaction/Conslidation |
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What is Primary porosity?
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Porosity that was developed at deposition.
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What is secondary porosity?
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Porosity that was developed after the sediments were deposited (dissolution pores of clastics or carbonates)
cementation (clays) fractures |
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What are the 6 factors that affect permeability?
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size and shape of grains
sorting rock - fluid interactions (dissolution/cementation) fractures stress formation damage |
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What are the three types of clay distribution and their relative effect on porosity?
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Dispersed clay (slight affect)
Laminated Clay (Greatest affect) Structural clay ( little affect) |
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What are the 4 components of a sandstone?
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framework
Matrix cement pores |
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What are the 7 carbonate porosity types?
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interparticle
intraparticle intercrystal moldic fenestral fracture vug |
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What is Transit time?
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The reciprocal of velocity also known as sonic slowness. Measured in micro-seconds/ft
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What fluoresceses under a black light in core samples?
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Oil
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What do emitted gamma rays measure? What is emitted gamma ray tool known as?
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Emitted gamma ray tool is known as a density tool.
They measure porosity, density, and lithology |
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What does a neutron tool measure?
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porosity?
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What two curves can a density log give?
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Bulk density and Photo electric effect.
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Why are density/neutron logs better than sonic for determining porosity?
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Density/neutron tools can find porosity without knowledge of rock matrix.
There's not need for a compaction correction with them Shale effects are more evident Transitions from one type to another are detected. Overlay of density-neutron excellent indicator of gas. |
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How does an active gamma ray tool work?
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The gamma ray is emiteed from a radioactive source in the sonde.
The gamma rays collide with electrons in the formation which causes them to lose energy. As the gamma rays bounce back to the tool, detectors measure the intensity of the backscattered gamma rays. |
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What does high energy gamma rays determine?
Low energy? |
High energy = density
Low energy = lithology |
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How do gamma rays interact with matter?
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Pair production
Compton scattering Photoelectric Adsorption |
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Is Pair production important when looking at density tools?
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No, because the source strength is .662 MeV and it requires 1.02 MeV for a photon to create an electron and positron.
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What is the compton scattering effect?
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When medium to high energy gamma rays hit the formation they are scattered. This can be measured to determine the density of the formation.
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What is the photoelectric effect?
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When low energy gamma rays collide with the formation they are absorbed by atoms. The greater the atomic number of the formation, the more gamma rays absorbed. This can show what atomic number the formation is.
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What does bulk density depend on?
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lithology
formation porosity density and saturation of fluids in pores |
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The density correction curve measures quality. At what measures must it be thrown out at?
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If it's less than .05 (there's no pad contact)
If it's greater than .2 (it's too large) |
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When density logs tracks gas, what occurs?
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The gas will cause the density to drop anomalously low which creates a high porosity
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What kind of holes can neutron logs be used in?
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Any kind
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What is a neutron log used for?
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identifing porous zones
determining porosity identifying gas in porous zones. |
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How does a neutron tool work?
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It sends out a neutrons that are bounced back after losing energy and sensed by a detector. High counts = low porosity
Low counts = high prosity |
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Why are neutrons used for a porosity tool?
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Neutrons responds primarily to the presence of hydrogen, and hydrogen is in the pores in either water or HC content
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What affects the neutron porosity tool?
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Lithology
Gas Shale |
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What happens with neutron porosity readings when it runs through gas?
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A neutron tool interprets gas to be water occupying a smaller volume. This causes it to show an anomalously low porosity
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How does a neutron log read shale when it runs?
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Since the neutron tool responds to the presence of hydrogen in the bound water, there is an anomalously high porosity
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What is the gas effect?
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When a neutron log reads too low and a density log reads too high, there is a crossover that shows gas.
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What are common porosity crossplots?
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Neutron-density
Sonic neutron Sonic density |
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What is the most used crossplot?
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Neutron - density
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What are common readings for salt on a neutron-density logs?
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neutron posity is slightly less than zero. Density porosity is 40 porosity units or more.
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What are common readings for anhydrite on neutron-density logs?
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Neutron porosity is greater than density porosity by 14 porosity units or more and neutron porosity is around 0
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What are common readings for dolomite on neutron-density logs?
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Density is greater than neutron porosity by 12-14 porosity units.
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What are Mid plots used for?
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Mineral Identification
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What are resistivity devices used for?
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Identifying permeable zones
discriminating HC from water saturated zones Finding Sw Estimate moveable hydrocarbons determining resistivity porosity correlate strata |
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What are the two families of resistivity devices?
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Electrode tools (resistive)
Induction tools |
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When should induction logs be run?
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Where there is non salt saturated mud where Rmf is greater than 3 rw
Where resistivity is greater than 200 in an oil based mud |
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When should Laterolog or dual laterologs be run?
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In salt saturated drilling mud where Rmf ~ Rw
Where resistivity is greater than 200 Where there are thin beds |
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What is resistivity?
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the voltage required to cause current of one amp to pass through a cube having a face area of one square meter. Resistivity = 1/conductivity
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Why uses resistivity instead of resistance?
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Resistance is a function of distance.
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What affects a resistivity tool?
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the invasion of mud filtrate
Mud in the borehole the resistivity of the shoulder beds mud cake |
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How does an electrode tool work?
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Works by sending an electrical current through electrodes into the formation (requires water based muds)
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How does an induction tool work?
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It generates a magnetic field that induces a current in the formation. (requires oil-based, air, or fresh water muds)
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What is the azimuthal resistivity tool used for?
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Thin bed analysis
Azimuthal resistivity Fracture detection Rt in dipping beds |
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What is the difference between UBI and FMI?
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UBI shows topography
FMI shows resistivity |
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When do you not assume Deep resistivity reads Rt (True Resistivity)?
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Rt/Rm is greater than about 10
Rt/Rs is greater than about 10 Hole size is greater than about 12 inches the bed is thinner than about 15 feet invasion diameter is greater than about 40 inches |
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What is spherically focused resistivity measurement used for?
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Shows a shallow resistivity and is good for thin bed detection
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What measures the resistivity of the flushed zone (Rxo)?
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MicroSFL
Microlaterology Microguard Proximity |
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Microresistivity tools are used as Rxo measurement tools because?
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They have a very high vertical resolution
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In order of least resistive to most resistive list the resistivity of the earth materials
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Salt water
fresh water oil gas rock |
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What factors affect resistivity?
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resistivity of water
porosity of the formation pore geometry lithology of the formation degree of cementation type and amount of clay in rock |
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What is Archies first equation?
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Ro = F*Rw
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What does the formation factor depend on?
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Porosity of the formation
Pore geometry lithology of the formation degree of cementation and type and amount of clay in the rock |
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If you have a clean formation what is the formula for formation factor?
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F = a/(Porosity^m)
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What is Archies Second equation?
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An equation relating Sw to Rt
Sw^n = Ro/Rt = (F*Rw)/Rt = (a*Rw)/(Porosity^m*Rt) |
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Shaly sand conductivity varies with what?
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Clay type
shale origin Fluid composition |
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When in shaly formations, fresh formation water causes what (in terms of water saturation)?
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Conventional log analysis to overestimate water saturation
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When in shaly formation, salty formation waters cause what?
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Low resistivity which may cause pay zones to be bypassed
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When in shaly formations, thinly bedded zones cause what?
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Conventional log analysis to underestimate porosity and overestimate water saturation
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What is shale?
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A type of clastic sedimentary rock that is comprised dominantly of clay minerals and other clay size fragments. However it does contain some silt size grans of quatz, feldspars, and other minerals.
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What is clay?
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Clay is a class of clastic sediments with a grain size < .004 mm
It is the name for a family of aluminosilicate minerals including: Kaolinite illite smectite montmorillonite chlorite |
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What are the different shale/clay occurrences?
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Dispersed clay
Clay lamination Structural Clay |
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Structural shale affects porosity and permeability in what way?
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It usually doesn't
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Laminated Shale affects porosity and permeability in what way?
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Significantly Reduces porosity and permeability
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Dispersed Shale affects porosity and permeability in what way?
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It depends on the different type of clay minerals, but will slightly reduce porosity and permeability.
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What is Diagenesis?
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Post-depositional chemical and mechanical changes that occur in sedimentary rocks.
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What are compaction diagenetic effects?
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Compaction
Precipitation of cement Dissolution of framework grains and cement |
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What are the different clay types?
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Kaolinite
Chlorite Illite |
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What are some properties of kaolinite?
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High Swi
Migration of fines problem not recognized by gamma ray Significant perm reduction |
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What are some properties of chlorite?
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Iron-rich varieties react w/ acid
occus as thin coats on detrital grain surfaces |
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What are some properties of illite?
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significant perm reduction
negligible porosity reduction High Swi Migration of Fines problem |
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What shale volume/water satruation formula would you use in a saline formation water that can correct for shale?
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Simandeaux
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What water saturation formula would you use in a fresh formation water that can correct for shale?
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Indonesia
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What are common shale volume calculation assumptions?
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Response in nearby shale gives 100% shale
Some intervals have 0% shale Shale in formation is the same as nearby shale |
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Which water saturation formula uses Cation Exhchange Capacity?
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Waxmin-Smits
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What do water saturation models don't use volume of shale?
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Double-layer models
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What kind of information can you get from a core?
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Porosity and permeability
Satruation Sedimentology Mineralogy Size of features below log resoultion |
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What are the two types of cores?
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Sidewall cores
Whole core |
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What is the most common lab core analysis? When is it not reliable?
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Plug
When there is a heterogeneous formation |
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What lab core analysis yield more accurate results? Why is it used less?
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Whole core analysis
Far more expensive |
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What effect does overburden stress have on the permeability of clastic rocks?
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The overburden stress decreases permeability, there is a very large difference between unconsolidated sands at formation pressure and surface pressure.
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What are the common core-log correlations?
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Depth matching
Comparing common measurements normalization defining net pay permeability prediction comparing saturations |
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How does one depth match core data to log data?
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Pick one log curve as reference and look for events giving abrupt changes. Then shift core data to match logs.
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What is static net pay?
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Resource and reserve calculations.
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What is dynamic net pay?
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Net pay that will flow from the reservoir.
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What are the 4 methods to determine net pay?
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Volumetric
Dynamic Production History Analogy |
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What does an isopach map measure?
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It measures the the true thickness. The one perpendicular to the surface of the formation
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What does an isochore map measure?
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The vertical thickness of the zone.
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What are the 4 drive mechanisms?
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Depletion Drive
Gas Cap Drive Water Drive Gravity Drive |
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What are the two types of depletion drives and their primary recovery percent?
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Solution gas (18-25%)
Expansion (2-5%) |
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What is the primary recovery percentage of a gas cap drive?
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20-40%
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What are the two types of water drive and their primary recovery percentage?
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Bottom (20-40%)
Edge (35-60%) |
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What is the primary recovery percentage of a gravity drive?
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50-70%
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What is dynamic net pay based on? What do you use to find it?
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Darcy's Law
Need flow based criterion Calibrate to well test or production flowmeter |
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What are some uses for capillary pressure?
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Determine initial water saturation
Determine fluid distribution in the reservoir Determine residual oil saturation for water flooding applications Determine pore distribtution index identify zones or rock types |
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What is the definition of capillary pressure?
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the pressure difference existing across the interface separating two immersible fluids
Pc = P nonweeting - P wetting |
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What is the free water level?
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The level at which water-oil capillary pressure is zero
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What is Drainage?
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Fluid flow process in which the saturation of the nonwetting phase increases
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What is imbitition?
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Fluid flow process in which the saturation of the wetting phase increases and the nonwetting phase saturation decreases
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What 6 reservoir properties have an effect on capillary pressure?
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Variations in permeability
Grain size distribution Saturation history Contact angle Interfacial tension Density difference between fluids |
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How does capillary pressure react to changes in permeability?
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The capillary pressure increases as permeability decreases
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How does capillary pressure react to changes in grain size distribution?
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The better the sorted the grains, the lower the capillary pressure
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How does capillary pressure react to changes in of contact angle?
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Capillary pressure increases as the contact angle decreases
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How does capillary pressure react to changes in density difference?
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Smaller density difference between fluid results in a larger transition zone
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How does capillary pressure react to changes in interracial tension?
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As interfacial tensions decreases it indicates a higher tendency of phase to mix together, which means capillary pressure decreases
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What is the Leverett J-Function originally used for for?
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To convert all capillary pressure data to a universal curve. Impossible to generate because of the extreme variation of rock properties and their affect on capillary pressures in reservoir
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What are the 4 methods for Measuring Capillary Pressure?
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Porous diaphragm method
mercury injection centrifuge method dynamic method |
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What are some advantages and disadvantages of the porous diaphragm method?
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Advantages:
Very accurate Can use actual reservoir fluids Disadvantages Very slow Pressure is limited by displacement pressure |
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What are some advantages and disadvantages of the Mercury injection method?
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Advantages:
Results obtained quickly Method is reasonably accurate Disadvantages: Ruins core difficult to relate merucry capillary data to oil/water or gas/water systems |
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What are some advantages and disadvantages of the centrifuge method?
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Advantages
Results can be obtained quickly Reasonably accurate Can use actual reservoir fluids Disadvantages Occasional data analysis or conversion problems |
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What are some advantages and disadvantages of the dynamic method of finding capillary pressure?
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Advantages:
Simulates reservoir conditions Can use actual reservoir fluids Disadvantages Very tedious to perform Costs are higher |
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What are some uses for effective and relative permeability?
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Reservoir simulation
Flow calcuations that involve multiphase flow in reservoirs estimation of residual oil (and/or gas) saturation |
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What is permeability?
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A property of the porous medium and is a measure of the capacity of the medium to transmit fluids.
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What is absolute permeability?
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When the medium is completely saturated with one fluid, then the permeability is absolute permeability
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What is effective permeability?
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The permeability to a particular fluid when the rock pore spaces contain more than one particular fluid
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What is relative permeability?
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The ratio of effective permeability to absolute permeability
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What are factors that affect permeability?
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Fluid saturations
geometry of the rock pore spaces and grain size distribution rock wettability fluids saturation history |
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What are the two lab methods for measuring relative permeability
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Steady state flow method (Hassler method, Penn State Method, Hafford's Method, Dispersed Feed Method)
Displacement method |
