Kerogen_kinetics

Contents

Data Structure: Kerogen_kinetics
Description	Defines the assignment and processing data associated with Kerogen_kinetics definition
Usage	Kerogen_kinetics NUM=ival where ival is the data structure number

Description

Overview

This data structure defines the assignment and processing data associated with kerogen kinetics.

Screening of potential source rocks is performed by measurement of total organic carbon (TOC) content and Rock-Eval type pyrolysis yield (S1 and S2; sometimes P1 and P2), where:

•S1 = the amount of free hydrocarbons (gas and oil) in the sample.

•S2 = the amount of hydrocarbons generated through thermal cracking of non-volatile organic matter.

Reactive kerogen is thermally degradable: it is defined by the pyrolysis S2 yield and when the S2 yield is normalized to the TOC, the ratio is known as the hydrocarbon index (HI)

HI therefore provides an indication of the reactive to inert kerogen proportions in the sedimentary organic matter (SOM).

Hydrocarbon yields are reduced to carbon equivalents using a factor W (e.g. W=0.85 ), which is the weight fraction of carbon in hydrocarbons. However, S1 sometimes is implicitly defined considering W, so that in this case W=1.0 (default value in ParaGeo).

The ratio of gas generated relative to oil ( G) is also defined. G differs from the often used expression ( GOGI ), but they are related (see Pepper and Corvi, 1995 Figure 2) reproduced here.

kinetic_012

The equivalent fractional carbon concentrations relative to the initial total carbon mass are then:

and the reactive kerogen is defined as

Key indices and quantities defining the conversion of kerogen to hydrocarbon are:

kinetic_008

kinetic_011

Note that Transformation ratio TR is also referred to as Transformation index TI in the manual.

Five pre-defined kerogen types are available defined by the organofacies presented by Pepper and Corvi (1995) (see table):

Name	Description	Principal Biomass	Sulphur	Environmental/Age	Possible IFP Classification
A	Aquatic, marine, siliceous or Carbonate/evaporite	Marine algae, bacteria	High	Marine, upwelling zones, clastic-starved basins (any age)	Type II'S'
B	Aquatic, marine, siliciclastic	Marine algae, bacteria	Moderate	Marine, clastic basins (any age)	Type II
C	Aquatic, non-marine, lacustrine	Freshwater algae, bacteria	Low	Tectonic non-marine basins, minor on coastal plains (Phanerozoic)	Type I
DE	Terrigenous, non-marine, waxy	Higher plant cuticle, resin, lignin, bacteria	Low	Some (Mesozoic and younger) 'ever-wet' coastal plains	Type III'H'
F	Terrigenous, non-marine, wax-poor	Lignin	Low	Coastal plains (Late Palaeozoic and younger)	Type III/IV

Alternatively user defined kerogen types may be defined using a Gaussian description or tabular definition of weights and activation energies.

Default kerogen - > oil generation kinetic parameters for the pre-multiplier A0, activation energy Emean and the variance σ for the five organofacies presented by Pepper and Corvi (1995a) are listed in the table below:

Name	A0 (1/s)	Emean (KJ/mol)	σ (KJ/mol)
A	2.13E+13	206.4	8.2
B	8.14E+13	215.2	8.3
C	2.44E+14	221.4	3.9
DE	4.97E+14	228.2	7.9
F	1.23E+17	259.1	6.6

Default kerogen - > gas generation kinetic parameters for the pre-multiplier A0, activation energy Emean and the variance σ for the five organofacies presented by Pepper and Corvi (1995a) are listed in the table below:

Name	A0 (1/s)	Emean (KJ/mol)	σ (KJ/mol)
A	3.93E+12	206.7	10.7
B	2.17E+18	278.7	18.4
C	2.29E+16	250.4	10.1
DE	1.88E+11	230.6*	7.7
F	1.93E+16	275.0	9.9

•*Pepper and Corvi (1995a) have deemed the default value of Emean =206.4 kJ/mol unreliable and unrealistic, thus the default is defined as 230.6 KJ/mol based on results calibrated to the reference solution.

Other default parameters in the kerogen kinetics for the five organofacies presented by Pepper and Corvi (1995) are listed in the table below:

Name	Transformation ratio*, TR	Hydrocarbon index, HI	Gas concentration ratio, G	Weight fraction carbon, W
A	0.033	0.617	0.17	0.80
B	0.018	0.592	0.17	0.75
C	0.020	0.600	0.13	0.68
DE	0.007	0.333	0.23	0.68
F	0.002	0.158	0.44	0.75

•*Note that Transformation ratio TR is also referred to as Transformation index TI in the manual.

References

•Pepper, A.S. and Corvi, P.J. Simple kinetic models of petroleum formation. Part I: oil and gas generation from kerogen. Marine and Petroleum Geology. 12(3) 291-319. 1995

•Pepper, A.S., Dodd, T.A. Simple kinetic models of petroleum formation. Part II: oil-gas cracking. Marine and Petroleum Geology. 12(3) 321-340. 1995.

•Pepper, A.S. and Corvi, P.J. Simple kinetic models of petroleum formation. Part III: Modelling an open system. Marine and Petroleum Geology. 12(4) 417-452. 1995.

Name of kerogen data

Kerogen facies type

Defines the properties for Kerogen->Gas conversion via a Gaussian distribution

Kerogen gas table

Defines the properties for Kerogen->Oil conversion via a Gaussian distribution

Kerogen oil table

Total organic carbon by weight TOC

Transformation index TI (Also referred to as Transformation ratio TR)

Initial hydrocarbon index (HI)

Gas concentration ratio

Mass of reactive kerogen

The weight fraction of carbon in hydrocarbons W

Thickness of kerogen layer

Kerogen reaction count

Defines the universal gas constant R

Defines the density of kerogen

Hydrocarbon density type

Density of combined oil and liquid gas

Defines whether groups assigned kerogen are initialised as kerogen present or not.