02 petroleum geology
TRANSCRIPT
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Formation Evaluation Fundamentals
Petroleum GeologyThe contents of this presentation are fortraining purposes and internal use ONLY and
are NOT to be used for external use orcustomer presentations, as they may containsensitive information.
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Objectives
After completing this module, the student can:
Describe theories of origin of hydrocarbons.
Describe how oil migrates from source rocks throughcarrier rocks to reservoir rocks.
Identify structural and stratigraphic traps.
Describe lithological properties of various types ofreservoir rocks.
Differentiate between porosity and permeability.
Describe fluid saturation
Compare an undisturbed formation with an invadedformation in terms of fluid contents.
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Hydrocarbon Sources
Inorganic
Organic
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Inorganic Hydrocarbon Sources
Assumes that some combination of chemical reactionoccurs naturally to form petroleum and coal.
Receives little support today.
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Organic Hydrocarbon Sources
Claims that fossil fuels were formed from remains ofplants and animals.
Plant and animal remains were transformed intopetroleum by:
Bacterial action
Heat and pressure
Catalytic reactions
Radioactive bombardments.
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Organic Hydrocarbon Sources
Burial
Chemical Reactions Pressure Time
Radioactive
BombardmentBacterial Action Heat
Petroleum
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Migration and Accumulation
Migration is the natural movement of oil from sourcerock to reservoir rock.
Migration influences include:
Buoyancy
Hydrodynamics
Capillary action
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Buoyancy
Basic mechanism involved in migration ofhydrocarbons.
Occurs because petroleum is lighter than water.
Oil will naturally rise to set on top of water.
Gas will naturally rise above oil.
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Hydrodynamics
Hydrodynamics are the forces by which one fluidflows past another carrying the second fluid with it.
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Hydrodynamics
Sandstone Bed
Confining Bed
(Shale)
Confining Bed(Shale)
Oil Accumulation
Underground Water Flow
Hydrodynamic Forces of Underground WaterFlow Drag Oil Droplets along with Water
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Capillary Action
Capillary action is the tendency of a fluid to rise in asmall tube or the way a sponge soaks up water.
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Capillary Action
Oil is absorbed into by capillary action.
Dry Sandstone
Oil-filled Sandstone
SandGrain
OriginalOil Level
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Accumulation
Buoyancy, hydrodynamics, and capillary action causethe fluids to migrate from source rock to reservoirrock.
Reservoir rock must have a cap rock or a confiningbed next to it to seal the reservoir.
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Accumulation
Confining Bed(Cap Rock)
SourceRock
Confining Bed
Fault Boundary
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Reservoir Traps
Structural Traps Result from rock layer deformation.
Stratigraphic Traps
Result when a reservoir bed is sealed by other beds Result when porosity or permeability change within a
reservoir bed.
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Structural Traps
A few examples of structural traps are: Anticline
Syncline
Fold
Fault
Salt Dome
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Structural Traps
An anticline is anelongated fold inwhich the sides slope
downward from thecrest.
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Structural Traps
A syncline is adepressed fold betweentwo crests.
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Structural Traps
A fold is a bend orflex in a layer orlayers of rock.
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Structural Traps
A fault is a break in theearths strata.
Often strata on one sideof the fault line havebeen displaced relativeto their original positions.
Upward
Downward Laterally
OilSaltWater
Gas
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Structural Traps
An example ofa fault.
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Structural Traps
A salt dome (diapir) isan anticlinal uplift ofsedimentary rocks
caused by the pushingup of a body of salt.
The uplift is typicallyspherical.
Oil
Oil
Oil
Salt
Gas
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Stratigraphic Traps
Stratigraphic Traps: Result when a reservoir bed issealed by other beds or when porosity or permeabilitychange within a reservoir bed.
A few examples of stratigraphic traps are:
Lens
Unconformity
Pinchout
Porosity Trap
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Stratigraphic Traps
A lens is anisolated body ofsedimentary rock,
such as a reef or asand bar.
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Stratigraphic Traps
An unconformity is asurface that separatesone set of rocks fromanother younger set.
An unconformityrepresents a period ofnon-deposition,weathering, or erosion,either sub-aerial or sub-
aqueous, prior to thedeposition of the youngerset.
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Stratigraphic Traps
A pinchout is thenatural ending of asedimentary rock
regressive sands
transgressive sands
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Stratigraphic Traps
A porosity trap iscreated because ofvariations in porosity
within rock. It can also be created
with secondaryporosity.
Oil
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Reservoir Rock
Almost all reservoir rocks are sedimentary.
Sedimentary rocks include:
Sandstone
Conglomerate
Limestone
Dolomite
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Reservoir Rock
Sand
Loose, uncompacted (unconsolidated) quartz or feldspar.
Sandstone
Compacted (consolidated) quartz or feldspar.
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Reservoir Rock
Waterwith
Solids
Sandstone CementedSandstone
Void SpacesVoid Spacesfilled (Cemented)
RockParticles
Cementation can decrease or increase porosity. Example: cementation by fluid movement
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Reservoir Rock
Conglomerate
A cemented clastic rock containing rounded rock fragmentsof gravel, pebble size.
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Reservoir Rock
Limestone
Formed chiefly by accumulation of shells and coral
Consists mainly of calcium carbonate
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Reservoir Rock
AcidicWater
L i m e s t o n e
Small Void Spaces Large Void Spaces
Water as a dissolving agent.
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Rock Properties
Lithology is a description of the mineralogy and rocktype present.
Lithological types (and oilfield abbreviations) include:
SS: sandstone
LS: limestone
DOL: dolomite
SH: shale
SALT: crystalline salt
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Porosity
Porosity is the ratio of the void space in a rock to thebulk volume or size of the rock.
UnconnectedPore
Total Porosityincludes
Connected andUnconnected
Pores
Sand Grain
Effective Porosity(Interconnected Pores)
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Porosity
Porosity varies relative to grain shape andarrangement.
Normally porosity varies between 10% and 30%.
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Porosity
Cubic porosity providesthe maximum possibleporosity = 47%
When grains are stackedin a rhombohedralfashion, porosity = 26%
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Porosity
If formation consistsof varying sizedgrains in a closelypacked arrangement,porosity = 10%
If grains are bricklikeand loosely stacked,porosity = 1%
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Porosity
Types of porosity include: Total Porosity:
Ratio of total void space in a rock to the bulk volume ofthe rock.
Effective Porosity:
Portion of total pore space in saturated permeable rock inwhich movement of fluids takes place.
Ratio of interconnected pore space in a rock to bulkvolume of the rock.
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Permeability
Permeability is the ability of a rock to transmit a fluid. It is measured in millidarcies (md).
Permeability is a function of area, length, pressure,viscosity, and flow rate of the fluid.
Formations cannot be produced if permeability is lessthan 50 md.
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Permeability
Sand Grains
Pore Space
1 Atm
1 cm
1 cm2
Q = 1 cc/secVis = 1 cp
Formation CoreHaving Permeability
of 1 Darcy
Fluid flow in permeable sand
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Fluid Properties
Gas, oil, and water are the most commonly foundfluids in a reservoir rock.
Fluid saturation
Ratio between the volume that a specific fluid occupies in thereservoirs void space
Fluid saturation of the formations void space of a porous
rock is always 100%.
If the void space is said to be half filled with oil and half filledwith water, then the rock would have a 50% oil saturation (So)and a 50% water saturation (Sw)
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Fluid Saturation
Water saturation (Sw): percentage of formation fluidthat is water.
Oil saturation (So): percentage of formation fluid thatis oil.
Gas saturation (Sg): percentage of formation fluid thatis gas.
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Fluid Density
Fluid density describes the mass of formation fluids. Fluid density determines the location of different fluids
in a reservoir.
Gas has the lowest (lightest) density.
Water has the highest (heaviest) density.
Oil lies between gas and water in density.
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Effect of Fluid Densities
Water
Oil
Gas
Gas Cap
Aquifer
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Effect of Formation Water
Formation water wettingthe sand grains
PoreSpace
Sand Grain
Quartz
Limestone
Chert
Feldspar
Quartz
Quartz
Quartz
Clay
Clay
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Comparison Between Undisturbed and Invaded
FormationsInvaded
Formation
Mudcake
Filtrate
Washed OutHole
Sw = Irreducible
Sw = 100%
UndisturbedFormation
Oil
FormationWater
Shale