02 petroleum geology

8/3/2019 02 Petroleum Geology

1/48

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.


2/48

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.


3/48

Hydrocarbon Sources

Inorganic

Organic


4/48

Inorganic Hydrocarbon Sources

Assumes that some combination of chemical reactionoccurs naturally to form petroleum and coal.

Receives little support today.


5/48

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.


6/48

Organic Hydrocarbon Sources

Burial

Chemical Reactions Pressure Time

Radioactive

BombardmentBacterial Action Heat

Petroleum


7/48

Migration and Accumulation

Migration is the natural movement of oil from sourcerock to reservoir rock.

Migration influences include:

Buoyancy

Hydrodynamics

Capillary action


8/48

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.


9/48


10/48

Hydrodynamics

Hydrodynamics are the forces by which one fluidflows past another carrying the second fluid with it.


11/48

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


12/48

Capillary Action

Capillary action is the tendency of a fluid to rise in asmall tube or the way a sponge soaks up water.


13/48

Capillary Action

Oil is absorbed into by capillary action.

Dry Sandstone

Oil-filled Sandstone

SandGrain

OriginalOil Level


14/48

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.


15/48

Accumulation

Confining Bed(Cap Rock)

SourceRock

Confining Bed

Fault Boundary


16/48

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.


17/48

Structural Traps

A few examples of structural traps are: Anticline

Syncline

Fold

Fault

Salt Dome


18/48

Structural Traps

An anticline is anelongated fold inwhich the sides slope

downward from thecrest.


19/48

Structural Traps

A syncline is adepressed fold betweentwo crests.


20/48

Structural Traps

A fold is a bend orflex in a layer orlayers of rock.


21/48

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


22/48

Structural Traps

An example ofa fault.


23/48

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


24/48

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


25/48

Stratigraphic Traps

A lens is anisolated body ofsedimentary rock,

such as a reef or asand bar.


26/48

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.


27/48

Stratigraphic Traps

A pinchout is thenatural ending of asedimentary rock

regressive sands

transgressive sands


28/48

Stratigraphic Traps

A porosity trap iscreated because ofvariations in porosity

within rock. It can also be created

with secondaryporosity.

Oil


29/48

Reservoir Rock

Almost all reservoir rocks are sedimentary.

Sedimentary rocks include:

Sandstone

Conglomerate

Limestone

Dolomite


30/48

Reservoir Rock

Sand

Loose, uncompacted (unconsolidated) quartz or feldspar.

Sandstone

Compacted (consolidated) quartz or feldspar.


31/48

Reservoir Rock

Waterwith

Solids

Sandstone CementedSandstone

Void SpacesVoid Spacesfilled (Cemented)

RockParticles

Cementation can decrease or increase porosity. Example: cementation by fluid movement


32/48

Reservoir Rock

Conglomerate

A cemented clastic rock containing rounded rock fragmentsof gravel, pebble size.


33/48

Reservoir Rock

Limestone

Formed chiefly by accumulation of shells and coral

Consists mainly of calcium carbonate


34/48

Reservoir Rock

AcidicWater

L i m e s t o n e

Small Void Spaces Large Void Spaces

Water as a dissolving agent.


35/48

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


36/48

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)


37/48

Porosity

Porosity varies relative to grain shape andarrangement.

Normally porosity varies between 10% and 30%.


38/48

Porosity

Cubic porosity providesthe maximum possibleporosity = 47%

When grains are stackedin a rhombohedralfashion, porosity = 26%


39/48

Porosity

If formation consistsof varying sizedgrains in a closelypacked arrangement,porosity = 10%

If grains are bricklikeand loosely stacked,porosity = 1%


40/48

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.


41/48

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.


42/48

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


43/48

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)


44/48

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.


45/48

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.


46/48

Effect of Fluid Densities

Water

Oil

Gas

Gas Cap

Aquifer


47/48

Effect of Formation Water

Formation water wettingthe sand grains

PoreSpace

Sand Grain

Quartz

Limestone

Chert

Feldspar

Quartz

Quartz

Quartz

Clay

Clay


48/48

Comparison Between Undisturbed and Invaded

FormationsInvaded

Formation

Mudcake

Filtrate

Washed OutHole

Sw = Irreducible

Sw = 100%

UndisturbedFormation

Oil

FormationWater

Shale

02 petroleum geology

Documents