(5) Petroleum System

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PETROLEUM SYSTEM

1.GENERATIVE SUB SYSTEM2.MIGRATION SUB SYSTEM3.ENTRAPMENTS SUB SYSTEM

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Geochemical ProcessesGeochemical ProcessesApplied organic geochemistry has become an essential part of prospect evaluation.Few companies would acquire or relinquish acreage without first performing a geochemical analysis.The main concepts or processes we’ll be interested in are:

Source rock ACCUMULATIONMATURATION upon burialGENERATION of hydrocarbonsEXPULSION from the source rock

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GENERATIVE SUB SYSTEM

QUANTITY of organic matter TYPE of organic matter MATURITY of organic matter GENERATION of hydrocarbons EXPULSION of hydrocarbons

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Source Rock CriteriaSource Rock Criteria QUANTITY of organic matter TYPE of organic matter MATURITY of organic matter GENERATION of hydrocarbons EXPULSION of hydrocarbons

%TOC Grade< 0.5 Very Poor0.5 – 1.0 Poor1.0 – 2.0 Fair2.0 – 4.0 Good4.0 – 12.0 Excellent> 12.0 Oil Shale / Coal

Typically, hydrocarbons are generated in a dark, organic-rich shale.Criteria that must be considered:

QuantityTypeMaturityGenerationMaturation

Quantity usually measured as TOC (Total Organic Carbon). A TOC = 1.0 means that organic carbon constitutes 1 percent dry weight of the rock.Typical source rocks have TOC values of above 1%, ideally 2.5 to 5%.Another modelling consideration is that PORTION of the source rock that has the high TOC content.The entire formation may be hundreds of feet thick. The portion rich in TOC may only be tens of feet thick.

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TYPE OF ORGANIC MATTER

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Soluble and insoluble organic matter in Soluble and insoluble organic matter in sedimentssediments

That part of organic matter which is insoluble in organic solvents is called KEROGEN.Typically comprised of plant remains.Soluble organic matter = bitumen.

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Kerogen TypesAs Determined by Visual Kerogen Analysis, Origin, and HC Potential

DepositionalEnvironment

Other PalynologySystem

KerogenForm

KerogenType

HydrocarbonPotential

Lacustrine LacustrineSapropel

Algal(Plankton)

Alginite I Oil

FluorescingAmorphous

FluorescingAmorphous

I or II Oil

Herbaceous Exinite II Oil/CondensateAquatic Marine " Resinite II "

Sapropel " Liptinite II "(typically " Suberinite II " marine) " Sporinite II "

" Cutinite II "Non-fluorescingAmorphous

Non-fluorescingAmorphous

III or IV Gas or None

Terrestrial Humic WoodyCellulose

Vitrinite

III Gas mainly.May have someoil potential,especially inSE Asia if"HI" is > 150.

Coaly Inertinite IV Dead CarbonNo Potential

(after Merril, 1991; Cornford, 1990)Each kerogen type will accumulate in a particular sedimentary environment.Each kerogen type is related to a type of plant material.Each kerogen type has a tendency to product a certain type of hydrocarbon.In BasinMod, we use the Type I, Type II Type III Classification.Type IV has no hydrocarbon potential - it is totally burned up.

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Evolution of Kerogen Composition with BurialEvolution of Kerogen Composition with Burial(after van Krevelen, 1961)

Plot ratio of atomic Oxygen to Carbon versus the ratio of atomic Hydrogen to Carbon.Points fall into 4 categories:High Hydrogen - Low Oxygen - Type IHigh Oxygen - Low Hydrogen - Type IV (remember high oxygen content being a negative indicator of hydrocarbon potential).

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Modified van Krevelen DiagramModified van Krevelen Diagram

From Waples, 1985

This Modified Van Krevelen diagram is what we can plot in BasinMod.

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Organofacies

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MATURITY

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Rock-Eval Pyrolysis

Attempt to simulate the hydrocarbon generation process in the laboratory. QUANTIFIES geochemical parameters.Rock is heated at a much HIGHER TEMPERATURE than in nature so generation occurs in a much SHORTER TIME than in nature.S1 represents hydrocarbons already present in the rock.Measured as mg HC per grams of TOC.S2 represents hydrocarbon formed by thermal degradation during pyrolysis. It is the most important indicator of the present-day ability of the kerogen to generate hydrocarbons.TMAX is the temperature at which the S2 peak occurs. It represents the temperature at peak generation.S3 represents the amount of carbon dioxide in the kerogen which is related to the amount of oxygen in the kerogen. High oxygen contents are related either to woody-cellulosic source material or to strong oxidation during diagenesis, high oxygen content of a kerogen is a negative indicator of hydrocarbon source potential.

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Rock-Eval PyrolysisRock-Eval Pyrolysis

After Waples, 1985

250-550°C

S1 = HC already present (250°C)

S2 = HC generated from the kerogen by thermal decomposition (420 - 460°C)

S3 = carbon dioxide given off by the kerogenTmax

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Indicator Notation Definition Equation Rating

TRANSFORMATIONRATIO

TRAmount ofkerogen trans-formed to HC

S1 HC exp _______ S1o + S2o

<0.1 = Immature 0.1 - 0.4 = Oil > 0.4 = Gas

PRODUCTIONINDEX

PIAmount of HCavailable forproduction

S1 _______ S1 + S2

HYDROGENINDEX

HI HydrogenContent

(S2x100) mg/g__________ % TOC

< 150: Gas 150 - 300: Mixed (RO = 0.6%) > 300: Oil

OXYGENINDEX

OI OxygenContent

(S3x 100)mg/g___________ % TOC

<40 mg/glow HI=land derived OM and/or maturehigh HI=good to excellent source potential>40 mg/glow HI=gas-prone OM,generally immaturehigh HI=good oil source, gen. immature

POTENTIAL YIELDOR HYDROCARBONSOURCEPOTENTIAL

PYPotential Yield(assuming im-maturesample)

(S1+S2) mg/g<2 mg/g Poor2-6 mg/g Fair>6 mg/g Very Good

KEROGEN TYPE Kerogen Type S2 _______ S3

<3: Gas Prone 3-5: Mixed >5: Oil Prone

THERMALMATURITY

TMAXTemperature atPeakGeneration

MeasuredTemperature atS2 (in deg C)

<430: Immature 430-460: Oil Generation >460: Gas Generation or destruction

INDICATIONS OFMIGRATEDHYDROCARBONS

(1) HIGH S1 (2) LOW Tmax (3) HIGH S1/%TOC (4) HIGH S1/(S1 +S2)

After Merrill, 1991

Description of Pyrolysis Data

Various relationships of these values, S1, S2, S3, TMAX and TOC, result in parameters which can define the kerogen type and, thus, the hydrocarbon prone-ness of the source rock containing the kerogen.

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Evolution of the S2 Pyrolysis Peak and TMAX with Maturation

Tissot, B.P., Pelet, R. and Ungerer, Ph., 1987, Thermal history of sedimentary basins, maturation indices, and kinetics of oil and gas generation, AAPG Bulletin, v. 71, p. 1445-1466.

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The Tmax (maximum S2 peak) varies as a function of the thermal maturity and the organic matter type. The Tmax is not an evolution parameter for Type I organic matter which is rapidly transformed when Ro varies from 0.7 to 1.0%.Type I - Green River Shale Oil genesis begins @ Ro 0.70% and ends @ 1.0 but Tmax remains constant.Type II - Oil genesis begins @ Ro = 0.60 - 0.65 % and Tmax - 435o C Oil/Gas @ Ro = 1.0 and Tmax of 455o C Gas and Condensate up to 470o CType II-S - Monterey ShalesType III - Oil genesis begins @ Ro = 0.60 - 0.70 % and Tmax > 435o C Oil/Gas @ Ro = 1.0 and Tmax of 455o C Condensate @ Ro = 1.30% and Tmax = 470o C Dry Gas Tmax = 540o C

Complete degradation at Ro = 1.60% and Tmax > 600o CTo create or edit Maturity and Kinetic Windows for different organic matter types:Determine the Tmax for each organic matter type window from this figure. Use these Tmax values in the next figure to determine equivalent TR and VR.

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Relationship between TMAX and Organic Relationship between TMAX and Organic Matter Type with Oil and Gas WindowsMatter Type with Oil and Gas Windows

Bordenave, M., 1992, (ed.), Applied Petroleum Geochemistry, Fig. 2-17, p.246

465

430

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0.78

1.08

0.1 0.45

430 465

Relationship of Transformation Ratio, TMAX, and %Ro to Kerogen Relationship of Transformation Ratio, TMAX, and %Ro to Kerogen TypeType

Bordenave, M., 1992, (ed.), Applied Petroleum Geochemistry, Fig. 2-27, p.254.

To create or edit Maturity and Kinetic Windows for different organic matter types:Determine the Tmax for each organic matter type window from previous figure. Use these Tmax values in this figure to determine equivalent Transformation Ratio and Vitrinite Reflectance.In BasinMod 1-D this is set in under Project/Global Data/Windows.

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Tmax v Ro

420

430

440

450

460

470

480

490

500

510

520

0 0.5 1 1.5 2 2.5

Ro

Tmax

Bmod default

Type I

Type II

Type III

Mix

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Rock-Eval Pyrolysis Rock-Eval Pyrolysis GeneralizationsGeneralizations

• Immature Source Rock– small S1 peak (small amount HC already

generated)– larger S2 peak

• Mature Source Rock– large S1 peak (more HC already generated)– smaller S2 peak, occurring at a higher temperature

than the immature sample due to increased thermal stability of the more mature organic matter

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Maturation and Generated HydrocarbonsMaturation and Generated Hydrocarbons

Modified from Dow, 1977

The level of source rock maturation can be measured optically by such methods a spore color index and vitrinite reflectance. Maturity can be calculated given the subsidence history of the rock and the geothermal gradient of the area.

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Correlation Table of Common Maturation Correlation Table of Common Maturation ParametersParameters

After Senftle and Landis, 1991, in Merril, R.K. (ed.) Source and Migration Processes and Evaluation Techniques, AAPG Treatise of Petroleum Geology, p. 120.

TAI - puts a numerical value on the color of organic material

TMAX - the temperature at peak generation in Rock Eval Pyrolysis.

If you have in-house maturity measurements, and they can be related to %Ro, they can be shown on a BasinMod Maturity versus Depth graph as “Measured Special”.

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Thermal Maturity

• Practical description of organic rich rocks at sufficient stage in thermal evolution to produce hydrocarbons of economic importance

• Empirically derived relationship between observed changes in organic material with increase in (generally) burial depth

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Thermal Maturity• Lopatin (TTI) Method

– Reaction Rate Doubles Every 10°C

•Limitations– Older Technology– Not Based on True Kinetic Parameters– Cannot Estimate Hydrocarbon Products

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Maturation as a functionMaturation as a functionof time and temperatureof time and temperature

Top diagram, same burial time, but different burial depths, resulting in different maturities for the 2 source rocks.

Bottom diagram, both source rocks have the same maturity: one source rock buried a long time at a shallow depth, the other buried for much less time at much greater depth.

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Thermal MaturityThermal Maturityand Chemical Historyand Chemical History

• Kinetic Models

– Based on the Arrhenius Law

• Based on Experimental Results• Better Prediction of Timing of Hydrocarbon

Generation• Predicts Hydrocarbon Volumes

Not only predicts hydrocarbon volumes, but gives a better prediction of the timing of hydrocarbon generation.

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Arrhenius EquationArrhenius EquationT h e b a s i c e q u a t i o n d e s c r i b i n g t h e r a t e ( K ) o f a c h e m i c a lr e a c t i o n i s t e r m e d t h e A r r h e n i u s E q u a t i o n :

)*( TREa

AK

W h e r e : K = r a t e o f t h e r e a c t i o n ( u n i t s : m y - 1 )A = f r e q u e n c y f a c t o r ( u n i t s : m y - 1 , s e c - 1 )E a = a c t i v a t i o n e n e r g y ( u n i t s : k c a l / m o l e )R = u n i v e r s a l g a s c o n s t a n t ( 8 . 3 1 4 3 2 j o u l e s / ° K )T = t e m p e r a t u r e ( ° K )

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Thermal Maturity and Chemical History

• Kinetic Models

– Tissot and Espitalié (1975)

– IFP (1988)

– Lawrence Livermore National Laboratories (LLNL) (1990’s)

– Geochemical Services (early 90’S)

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The concept of kinetic modelling requires That a reactant, such as Kerogen,has to absorb a certain amount of Kinetic Energy (such as Heat) in order that the Chemical Bonds break to form a product (such as oil or gas).

Start with kerogen, which contains carbon chains Increase energy to the System Chain bonds become unstable Chains break Result is product.

The reactant goes through an activated state once the level of energy is reached. The frequency of reaching this activated state is the Frequency Factor or Arrhenius Constant, usually measured in “per million years”.

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Energy Level Diagram Defining the Activation Energy Level Diagram Defining the Activation Energy and Frequency Factor in the Arrhenius Energy and Frequency Factor in the Arrhenius

EquationEquation

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Derivation of Activation Energy Distribution from a Pyrolysis S2 Curve

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Distribution of Activation Energies from the Green River Shales and Lower Toarcian Shales of

Paris Basin


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Distribution of Activation Energies from Miocene Coals and Coaly Shales of Mahakam Delta,

Indonesia

Tissot, B.P., Pelet, R. and Ungerer, Ph., 1987, Thermal history of sedimentary basins, maturation indices, and kinetics of oill and gas generation, AAPG Bulletin, v. 71, p. 1445-1466.

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Distribution of Activation Energies in Two High-Sulfur Kerogens From California and Iraq


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Primary Migration Primary Migration

Expulsion from the Source Rock

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Migration - Saturation Threshold TheoryMigration - Saturation Threshold Theory

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The mechanism of expulsion is still the subject of debate.One method is Porosity Saturation:As Maturation progresses, organic matter is transformed to oil.The generated oil fills pore spaces created by the destruction of kerogen.Oil fills the pore spaces, overcomes capillary resistance and begins to expel.Overpressure caused by the conversion of kerogen to oil and gas microfractures the rock and expels the fluid phase.In a lean source rock, not enough oil may be generated to fill the pore spaces. With continued burial, this trapped oil may crack to gas.

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Certain kerogens undergo generation at earlier maturity due to lower activation energies.These same kerogens can be expected to undergo earlier expulsion.Richer source rocks will accumulate greater volumes earlier that lean source rocks and, hence, begin to expel earlier.Another controlling factor is the sedimentary geometry of the source rocks. The expulsion efficiency is highest when the source rocks are thin and hydrocarbons have a short distance to migrate to more permeable carrier beds (meters, rather than tens of meters). Intercalated sandstones and shales would provide much greater expulsion efficiency than thicker bedded shales and sands.Rocks that are brittle and overpressured are likely to fracture, which dramatically enhances expulsion efficiency.

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The relationship The relationship between between

Production Index Production Index and and

TransformationTransformation Ratio Ratio

PI=S1(measured)/S1(orig)+S2(orig)

TR = S1(original)/S1(orig)+S2(orig)

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The area between the curves represents percent product expelled. This can actually be used as a calibrant.The hydrocarbon content of a rock consists of 2 things, free hydro-carbons already present (S1) and hydrocarbons yet to be created from the kerogen (S2).The production index (PI) is S1(measured)/S1(original)+S2(original). The sum of S1 and S2 in the denominator is always equal to 1. An immature source rock will have essentially no S1 which means the PI is zero. A mature source rock will have essentially no S2 which means the PI should be one....if no expulsion occurs. If a source rock never expels the PI is nothing more than the transformation ratio (S1(original)/S1(original)+S2(original)).As expulsion occurs, free hydrocarbons escape the rock which means S1(measured) will always be less than S1(original). So the PI in a maturing source rock will always be less than one but greater than zero.Plotting 'transformation ratio' and 'production index' on an X vs. Depth curve will show the percentage of hydrocarbons that have been expelled.Plot the measured (actually calculated PI) to calibrate.

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Expulsion Efficiency Expulsion Efficiency as a Function of Source Rock Richnessas a Function of Source Rock Richness

Certain kerogens undergo generation at earlier maturity due to lower activation energies.These same kerogens can be expected to undergo earlier expulsion.Richer source rocks will accumulate greater volumes earlier that lean source rocks and begin to expel earlier.

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Variation of expulsion efficiencies for oil, gas, and condensate with different kerogen types

Mackenzie & Quigley, 1988

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Hydrocarbons can be divided into 4 groups, dependent upon physical properties:

GAS (generally methane, CH4)CONDENSATE (wet gases in reservoir, liquid at surface)OIL (liquid: light, medium, and heavy oils)MINERAL HYDROCARBONS (solids: bitumen, asphalts, etc.)

Each type derives from a different combination of processes.

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Different Types of Reservoired OilsDifferent Types of Reservoired Oils

API gravity = (141.5/density) - 131.5

(5) Petroleum System

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