U.S. DEPARTMENT OF THE INTERIOR 

U.S. GEOLOGICAL SURVEY

Comparison of Kinetic-Model Predictions of Deep Gas Generation

by 

Allison A. Henry1 * and Michael D. Lewan1

Open File Report No. 99-326

This report is preliminary and has not been reviewed for conformity with U. S\ 

Geological Survey editorial standards (or with the North American Stratigraphic Code). 

Any use of trade, product, or firm names is for descriptive purposes only and does nc*. 

imply endorsement by the U. S. Government.

'U. S. Geological Survey, Box 25046, MS 977, Denver Federal Center, 

Denver, CO 80225 (e-mail: mlewan@usgs.gov)

* Current Address: The Scripps Research Institute, 10550 North Torrey Pines Road, La

Jolla, CA 92037

(e-mail: ahenry@scripps.edu)
INTRODUCTION

The source of and processes resulting in natural gas generation remain a 

controversial issue in petroleum geochemistry (Price, 1997). Various investigations have 

used different pyrolysis methods and organic sources to develop models to predict timing 

and quantities of natural gas generation in sedimentary basins (e.g., Table 1). The results 

and implications of these different models on predicting natural gas generation have not 

previously been compared in the literature. The objective of this study is to compare six 

different published gas-generation kinetic models (Table 1) with respect to their 

predictions of timing and quantities of deep-gas generation. As discussed by Dyman and 

others (1997), the potential for deep gas at depths greater than 4,572 meters (15,000ft) 

remains an uncertain domestic exploration frontier for natural gas. Two geological 

settings for the occurrence of deep gas emerge from this definition. The first geological 

setting envisages gas being initially generated and accumulating in traps at shallow 

depths (< 4,572 m/15,000 ft). As sedimentation and basin subsidence continue with 

geologic time, these shallow traps remain coherent and are eventually buried to depths 

greater than 4,572 m (15,000 ft). Deep-gas accumulations resulting from this setting are 

dependent on the competence of trap closures and seals with burial to depths greater than 

4,572 m/15,000 ft. The second geological setting envisages gas generation and 

accumulation in traps at deeper depths (>4,572 m/15,000 ft). Deep-gas accumulations 

resulting from this setting are dependent on a source of gas at burial depths greater than 

4,572 m/15,000 ft. It is this dependence on sources of deep gas generation that this study 

examines.

Various kinetic models for the generation of natural gas in sedimentary basins 

have been published over the last several years. These gas-generation kinetic models are 

primarily based on different types of laboratory pyrolysis methods, which include opensystem anhydrous pyrolysis (e.g., Rock-Eval; Behar and others, 1997), closed-system 

anhydrous pyrolsis (e.g., microscale sealed (MSSV) pyrolysis; Horsfield and others, 

1992), and closed-system hydrous pyrolsis (e.g., flexible gold-bag autoclaves; Knauss 

and others, 1997). In addition to employing different pyrolysis methods, different 

starting materials are considered as the source of natural gas. Some kinetic models 

consider crude oil in deeply buried reservoirs (e.g., Tsuzuki and others, 1997), and others 

consider unexpelled oil retained in mature source rocks (Pepper and Corvi, 1995).

These kinetic models are examined in two hypothetical basin scenarios that 

represent end-member heating rates of 1° and 10 °C/m.y. This study makes no attempt to 

judge the validity of the six kinetic models used, but only intends to present and compare 

their results and the implications they have on deep-gas generation. Kinetic models for 

the thermal stability of crude oil that are based on model hydrocarbons were not included 

in this study. Although these studies provide useful information on the influence of 

pressure, oil matrices, and cracking mechanisms (Domine, 1991; Behar and 

Vandenbroucke, 1996; Burnham and others, 1997), they are either based on the loss of 

the model compound rather than generated gas or the generated gases have peculiar gas 

compositions significantly different from natural gases.
METHODS 

Basin Scenarios

Gretener and Curtis (1982) have estimated common heating rates for sedimentary 

basins to be between 1° and 10 °C/m.y. In keeping with these limits, the kinetic models 

used in this study are compared in two end-member basin scenarios. One basin scenario 

uses a thermal gradient of 30°C/km and burial rate of 33.3 m/m.y., which results in a 

heating rate of l°C/m.y. The other scenario uses a thermal gradient of 45°C/km and 

burial rate of 222.2 m/m.y., which results in a heating rate of 10°C/m.y. The heating 

rates were assumed to be linear in both basin scenarios.

Kinetic Models

Attributes of the six kinetic models considered in this study are given in Table 1. 

Three of the models consider gas generation from kerogen (Behar and others; 1997, 

Pepper and Corvi; 1995; and Knauss and others; 1997). Behar and others (1997) used 

kerogen samples including a type-I kerogen from the Eocene Green River Fm., type-II 

kerogen from a Toarcian shale of the Paris basin, type-IIS kerogen from the Miocene 

Monterey Fm., and two type-Ill kerogens from a Miocene coal in the Mahakam delta and 

a Dogger coal from the North Sea. Pepper and Corvi (1995) organized their kerogen 

samples into organofacies A, B, C, D/E, and F. According to their definitions of 

organofacies, organofacies A kerogen is similar to type-IIS kerogen, organofacies B 

kerogen is similar to type-II kerogen, organofacies C kerogen is similar to type-I kerogen, 

organofacies D/E is similar to type III kerogen, and organofacies F is similar to typeIII/IV kerogens. Knauss and others (1997) used New Albany Shale (DevonianMississippian), which contains type-II kerogen.

The other three models consider gas generation from the cracking of oil (Horsfleld 

and others, 1992; Pepper and Dodd, 1995; and Tsuzuki and others, 1997). Horsfleld and 

others (1992) used of a medium gravity crude oil from a middle Jurassic reservoir in the 

Central Graben of the Norwegian North Sea (NOCS 33/9-14). Pepper and Dodd (1995) 

focused on the in-source cracking of oil as opposed to the cracking of reservoir oils; the 

authors used sixteen samples of source rocks classified as members of their five 

organofacies. Tsuzuki and others (1997) used a Sarukawa crude oil with an API gravity 

of33.6°.

Model/Pyrolysis Terminology

There are four types of models in this study that are based on different pyrolysis 

methods. The open pyrolysis model uses Rock-Eval pyrolysis to determine kinetic 

parameters (Behar and others, 1997). The composite pyrolysis model refers to Pepper 

and Corvi's (1995) mixed data set from many different references, natural data sets, and 

open- and closed-system pyrolysis methods. The anhydrous pyrolysis model refers to 

closed-system pyrolysis of kerogen or oil without liquid water and is used by Pepper and 

Dodd (1995) and Horsfleld and others (1992). The hydrous pyrolysis model refers tc 

pyrolysis of kerogen or oil in the presence of liquid water and is used by Knauss and 

others (1997) and Tsuzuki and others (1997).
Extent of Reaction with Single Activation Energy and Frequency Factor

As demonstrated by Wood (1988), the extent of a reaction (i.e., k = rate constant) 

that follows the Arrhenius equation,

k = A e-Jtp(-E/RT),

can be reasonably estimated over a linear heating rate by the approximate analytical 

integral solution derived by Gorbachev (1975):

TTlARR= {(A(tn+l-tn))/(Tn+l-Tn)}*{[(RT2n+l/(E+2RTn+l))*ejCp(-E/RTn+l)] - (1)

[(RTV(E+2RTn))*exp(-E/RTn)]}

where TTlARR is the extent of reaction function or time-temperature index, A is the 

frequency factor in m.y." 1 , E is the activation energy in cal/mol, R is the ideal gas constant 

in cal/mol-K, tn is the beginning of the time interval in m.y., tn+1 is the end of the time 

interval in m.y., Tn is the temperature in K at the start of the time interval, and Tn+1 is the 

temperature in K at the end of the time interval. TTlARR can be equated to the integrated 

first order rate equation,

ln(l/[l-X]) = kt, (2) 

by

TTlARR=ln(l/[l-X]) (3)

where X represents the extent of reaction as a decimal fraction, which is referred to ar 

fraction of reaction. TTlARR values can be calculated for various intervals in the burial 

history of a potential source rock using equation 1. The TTlARR calculated for each 

burial interval is additive and the sum values can be converted to fraction of reaction by 

solving equation 3 for X:

X=l-(l/e^?[TTlARR]). (4)

Tsuzuki and others (1997) derived single E and A values for the generation of C,- 

C5 hydrocarbon gas from the cracking of light (C6-C14 saturates) and heavy (C15H, 

saturates) components of crude oil. The activation energy and frequency factor for the 

cracking of the light component are respectively 86 kcal/mol and 6.4868 x 1035 m.y.-1 . The 

activation energy and frequency factor for the cracking of the heavy component are 

respectively 76 kcal/mol, 3.4187 x 1033 m.y.-1 . These kinetic parameters and the two endmember heating rates were used in equation 1 to determine the extent of gas generation 

from the cracking of oil in the two basin scenarios.
Extent of Reaction using Multiple Activation Energies or Frequency Factors

In order to reflect a first order reaction with more than one frequency factor or 

activation energy, X of equation 4 must also represent the fractional extent of reaction for 

each activation energy and frequency factor. Multiple activation energies or frequency 

factors are derived by curve-fitting methods that assume first-order parallel reactions. Thamultiple kinetic parameters are described as discrete or Gaussian distributions, with each 

of the multiple parameters being assigned a fractional part of the overall reaction 

(Ungerer and others, 1986; Braum and Burnham, 1987).

The discrete distribution is used by Behar and others (1997) and Horsfield and 

others (1992). Both groups optimized their experimental kinetic data in such a way to 

give a variety of activation energies with associated fractions of reaction and a single 

frequency factor. Behar and others (1997) present discrete activation-energy distribution^ 

for the generation of methane (C,) and C2-C5 hydrocarbon gas from five kerogens (Tabh 

2). Horsfield and others (1992) also use a discrete activation-energy distribution between 

50 and 73 kcal/mol with a frequency factor of 3.47 x 1029 m.y."1 for oil cracking to C,-C4 

hydrocarbon gas (Table 3). Equation 1 is used for each discrete activation energy for the 

fractional part of the reaction it is assigned and then summed with results from the other 

discrete activation energies to give a cumulative generation curve for the extent of 

reaction.

The Gaussian distribution of activation energies is employed by Pepper and Dodd 

(1995), Pepper and Corvi (1995), and Knauss and others (1997). The distribution is 

presented by a mean activation energy, Emean, and a standard deviation, CJE, as shown in 

Table 4. A Gaussian distribution is expressed by the equation

where cr is the standard deviation at the 68% confidence level (<JE), ^ is the mean 

activation energy (Emean), and Y is the height of the curve above a given X (discrete

activation energy). The function reaches a maximum value of j== when X = (j.

Using equation 5 and the parameters given by the cited authors, the Gaussian distribution 

was divided into discrete 1.0-kcal/mol activation energies. Since the area under the 

normal curve is one and each rectangle of discrete activation energy is one unit wide, the 

area of the rectangle becomes the fractional part of the reaction for a given discrete 

activation energy. When summed, the values at each discrete energy will equal one. 

Equation 1 is used for each discrete activation energy to determine the fractional part of 

the reaction it is assigned and then summed with results from the other discrete activatior 

energies to give a cumulative generation curve for the extent of reaction. Pepper and 

Corvi (1995) and Knauss and others (1997) used a different single frequency factor with 

each distribution, but Pepper and Dodd (1995) used the same single frequency factor for 

all of their activation energy distributions (Table 4).
Amount of Gas Generated

All of the kinetic models considered in this study employ first-order reaction 

rates, which give the extent of reaction, X, as a decimal fraction of the completed reaction 

at unity (i.e., X equals amount of gas generated at a particular thermal stress divided by 

the maximum amount of gas that can be generated from a particular source material). The 

obvious question that remains is how much gas per mass of starting material does unity 

equal? Behar and others (1997) explicitly state the maximum amounts (i.e., X = 1) of C, 

and C2-C5 generated from kerogen as given in Table 5. These values were combined to 

give maximum yields for C,-C5 in milligrams per gram of total organic carbon (mg/g C). 

Pepper and Corvi (1995) give maximum C,-C5 gas generation for each of their five 

organofacies: A = 105 mg/g C; B = 101 mg/g C; C = 78 mg/g C; D/E = 77 mg/g C; and F 

= 70 mg/g C.

The maximum gas concentrations reported as mmolal for the hydrous pyrolysis 

experiments by Knauss and others (1997) are converted to mg/g C by the equation

w

MW X Gmmolal X 

Gas (mg/gC)= * , (8)

where MW is the formula weight of the gas component (i.e., C, = 16.04 g/mol, C2 = 

30.07 g/mol, C3 = 44.10 g/mol, and C4 = 58.12 g/mol), Gmmola, is the maximum gas yield

w

in mmolal (Knauss and others, 1997; Table 2, p.482-483), is the watenshale ratio ft

s

time zero for the experiments (i.e., 4.06 g/g), and TOC is the total organic carbon of trn 

rock expressed as a fraction (i.e., 0.114). Equation 8 gives maximum gas yields cf 

26.5 mg/g C for methane (C,), 24.9 mg/g C for ethane (C2), 22.0 mg/g C for propane (C,) 

and 19.4 mg/g C for butane (C4). The total of these values (i.e., 92.8 mg/g C) gives trn 

maximum C,-C4 gas generated from the New Albany Shale (Table 5).

According to Pepper and Dodd (1995), the maximum amount of C,-C5 ga° 

generated from the cracking of oil in a source rock is equivalent to the amount of oil 

remaining in the kerogen after expulsion. Therefore, the maximum amount of gas for all 

sixteen kerogen samples is 100 mg/g C, which they consider the threshold for oil retained 

by sorption in the kerogen (Pepper, 1998, pers. comm.).

Horsfield and others (1992) experimentally determined that the maximum amount 

of C,-C4 gas generated from the cracking of reservoired oil by closed-system anhydrous 

pyrolysis is 460 mg/g oil. Tsuzuki and others (1997) considered gas generation from th^ 

cracking of reservoired Sarukawa oil by closed-system hydrous pyrolysis. The generation 

of C,-C5 gas is described by two reactions. One reaction (kll) involves the conversion of 

C, 5+ heavy saturates (C15+Sat) to CI5+ heavy condensed aromatics (C, 5+Aro), C,-C5 gas (C,- 

C5 ), and C6-C14 light saturates (C6-C!4Sat):

C15+ Sat *" ) 0.36(C15+Aro) + 0.27(C,-C5) + 0.37(C6-C!4Sat.) . (6)

The other reaction (k2) involves the conversion of the generated C6-C,4 light saturate? 

(C6-C,4Sat) generated in reaction 6 to C,-C5 gas (C,-C5 ) and insoluble coke (Cro):
C6-C14 sat. -^_> 0.60(C,-C5 ) + 0.40(0.,). (7)

Jamil and others (1991) report that C, 5+ heavy saturates (C, 5+Sat) comprise 64.9 wt. % of 

Sarukawa oils. Therefore, one gram of oil will initially generate 175 mg of C,-C5 gar 

through the cracking of C, 5+ heavy .Saturates (C, 5+Sat; equation 6) and an additional 14^ 

mg of C,-C5 gas through the cracking of C6-C, 4 light saturates (C6-C, 4Sat; equation 7). 

These two values are combined to give 319 mg/g oil as the maximum amount of gar 

generated from the cracking of oil.

RESULTS 

Kerogen to Gas

Figure 1 shows the gas-generation curves for Type-I kerogens in basins with 1° 

and 10 °C/m.y. heating rates as predicted by the open- and composite-pyrolysis models. 

At the top of the deep gas depth (4,572 m/15,000 ft), 91 and 64% of gas generation from 

Type-I kerogen is completed at l°C/m.y. according to the open- and composite-pyrolysis 

models, respectively. Therefore, 7.9 and 27.9 mg/g C of deep gas is generated 

according to the open- and composite-pyrolysis models, respectively (Figure la and 

Table 6). Both models predict that the deep gas generation is finished (i.e., X = 0.99) at 

depths of 6,800 and 5,600 meters (Table 6). At the top of the deep-gas depth (4,572 

m/15,000 ft), the open- and composite-pyrolysis models respectively predict 99 and 

100% of gas generation from Type-I kerogen is completed at 10°C/m.y. According tc 

these models, essentially no deep gas is generated from Type-I kerogen at this heating 

rate.

Figure 2 shows the gas-generation curves for Type-II kerogens in basins with 1° 

and 10 °C/m.y. heating rates as predicted by the open- and composite-pyrolysis models. 

At the top of the deep-gas depth (4,572 m/15,000 ft), 75, 67, and 35% of gas generation 

from Type-II kerogen is completed at l°C/m.y. according to the hydrous-, open-, and 

composite-pyrolysis models, respectively. These percentages indicate that 23.0, 22.9 

and 65.0 mg/g C of deep gas is generated according to the hydrous-, open-, and 

composite-pyrolysis models, respectively (Figure 2a and Table 6). Deep-gas generation 

is finished (i.e., X = 0.99) according to these three models at depths of 5,800, 6800, and 

7,200 meters (Table 6). At the top of the deep-gas depth (4,572 m/15,000 ft), the openand composite-pyrolysis models predict 92, 97, 95 and 100% of gas generation frorr 

Type-II kerogen is completed at 10°C/m.y., respectively. Therefore, according to these 

models essentially no significant amounts of deep gas are generated from Type-II 

kerogen at this heating rate.

Figure 3 shows the gas-generation curves for Type-IIS kerogens in basins with 1 ° 

and 10 °C/m.y. heating rates as predicted by the open- and composite-pyrolysis models. 

At the top of the deep-gas depth (4,572 m/15,000 ft), 74 and 93 % of gas generation frorr 

Type-IIS kerogen is completed at l°C/m.y. according to the open- and compositepyrolysis models, respectively. Therefore, 17.9 and 7.0 mg/g C of deep gas ir 

generated according to the open- and composite-pyrolysis models, respectively (Figure 3r 

and Table 6). These models predict that the deep gas generation is finished (i.e., X =
0.99) at depths of 6,400 and 5,000 meters (Table 6). At the top of the deep-gas depth 

(4,572 m/15,000 ft), the open- and composite-pyrolysis models predict 99 and 100% of 

gas generation from Type-IIS kerogen is completed at 10°C/m.y., respectively. 

Therefore, essentially no deep gas is generated from Type-IIS kerogen at this heating rate.

Figure 4 shows the gas-generation curves for Type-Ill kerogens in basins with 1 ° 

and 10 °C/m.y. heating rates as predicted by the open- and composite-pyrolysis models. 

At the top of the deep-gas depth (4,572 m/15,000 ft), 26 and 3 % of gas generation from 

Type-Ill kerogen is completed at l°C/m.y. according to the open- and compositepyrolysis models, respectively. Therefore, 39.7 and 73.8 mg/g C of deep gas is 

generated according to the open- and composite-pyrolysis models, respectively (Figure 4 a 

and Table 6). These models predict that the deep gas generation is finished (i.e., X = 

0.99) at depths of 6,400 and 7,000 meters (Table 6). At the top of the deep-gas depth 

(4,572 m/15,000 ft), the open- and composite-pyrolysis models predict 85 and 92 % of 

gas generation from Type-Ill kerogen is completed at 10°C/m.y., respectively. 

According to these models 7.9 and 6.0 mg/g C of deep gas is generated from Type-FI 

kerogen at this heating rate.

Figure 5 shows the gas-generation curves for more paraffinic Type-Ill kerogers 

(Type-IIF) in basins with 1° and 10 °C/m.y. heating rates as predicted by the open- and 

composite-pyrolysis models. At the top of the deep-gas depth (4,572 m/15,000 ft), 11 

and 3 % of gas generation from Type-Ill' kerogen is completed at l°C/m.y. according to 

the open- and composite-pyrolysis models, respectively. Therefore, 50.6 and 67.7 mg/g 

C of deep gas is generated according to the open- and composite-pyrolysis models, 

respectively (Figure 5 a and Table 6). These models predict that the deep gas generation 

is finished (i.e., X = 0.99) at depths of 7,800 and 7,000 meters (Table 6). At the top of 

the deep-gas depth (4,572 m/15,000 ft), the open- and composite-pyrolysis models 

predict 74 and 91 % of gas generation from Type-Ill kerogen is completed at 10°C/m.y., 

respectively. According to these models 14.9 and 6.0 mg/g C of deep gas is generated 

from Type-Ill' kerogen at this heating rate.

Source-Rock Oil to Gas

The anhydrous pyrolysis model by Pepper and Dodd (1995) considers the kinetics 

of gas generation exclusively from the cracking of unexpelled oil retained in a source 

rock after the main stages of oil generation and expulsion are completed. Figure 6 shows 

their model's predicted gas-generation curves for oil retained in 16 source rocks in basins 

with 1° and 10 °C/m.y. heating rates. These gas-generation curves are similar for all 16 

source rocks irrespective of kerogen type or rock mineralogy. As a result, the gasgeneration curve of the St Medard (SM) source rock serves as a representative average for 

this anhydrous pyrolysis model (Table 6). At the top of the deep-gas depth (4,572 

m/15,000 ft), 35 % of gas generation from oil retained in a source rock is completed ft 

l°C/m.y. Therefore 65 mg/g C of deep gas is generated (Figure 5a and Table 6). This 

model predicts that the deep gas generation is finished (i.e., X = 0.99) at a depth of 6,600 

meters (Table 6). At the top of the deep-gas depth (4,572 m/15,000 ft), this models 

predicts 100 % of gas generation from oil retained in a mature source rock is completed st
10°C/m.y. Therefore, according to this model essentially no deep gas is generated from 

oil retained in a source rock at this heating rate.

Reservoir Oil to Gas

Generation of gas from the cracking of oil in reservoirs is considered by the 

anhydrous- and hydrous-pyrolysis models by Horsfield and others (1992) and Tsuzuki 

and others (1997), respectively. Figure 7 shows the gas-generation curves for reservoir-oil 

cracking in basins with 1° and 10 °C/m.y. heating rates as predicted by the anhydrousand hydrous-pyrolysis models. At the top of the deep-gas depth (4,572 m/15,000 ft), 2 

and zero % of gas generation from reservoir-oil cracking is completed at l°C/m.y. 

according to the anhydrous- and hydrous-pyrolysis models, respectively. Therefore, 

449.5 and 320.2 mg/g oil of deep gas is generated according to the closed anhydrousand hydrous-pyrolysis models, respectively (Figure 7a and Table 6). These models 

predict that the deep gas generation is finished (i.e., X = 0.99) at depths of 7,600 and 

7,400 meters (Table 6). At the top of the deep-gas depth (4,572 m/15,000 ft), the 

anhydrous- and hydrous-pyrolysis models predict 80 and 53 % of gas generation from 

reservoir-oil cracking is completed at 10°C/m.y., respectively. According to these 

models at 10°C/m.y., 459.6 and 320.2 mg/g oil of deep gas is generated from reservoir oil 

cracking when reservoirs reach depths of 4,200 and 5,200 meters, respectively.

DISCUSSION 

Kerogen to Gas

Gas generation from kerogen at deep depths is more likely at slow basin heating 

rates irrespective of kerogen type or kinetic model (Table 7). At the slow heating rate of 

1 °C/m.y., 5 to 75 mg/g C of deep gas can be generated irrespective of kerogen type or 

kinetic model. In contrast, at the fast heating rate of 10 °C/my, only 0 to 15 mg/g C of 

deep gas is generated irrespective of kerogen type or kinetic model (Table 7). The 

implication here is that only a finite amount of gas can be generated from kerogen within 

a specific thermal-stress interval. Slow heating rates result in lower temperatures at 

greater depths, which allows this thermal-stress interval to be extended to greater depths 

within a basin. Therefore, according to these models, deep basins with cooler subsurface 

temperatures are more likely to generate deep gas from kerogen than deep basins witl' 

hotter subsurface temperatures.

For the slow heating rate, the composite-pyrolysis model predicts the greatest 

amount of deep gas, with values ranging from 5 to 75 mg/g C (Table 7). The open 

pyrolysis model gives lower values for deep-gas generation with a range from 8 to 51 

mg/g C (Table 7). However, at the rapid heating rate, the open-pyrolysis model predict" 

greater amounts (1 to 15 mg/g C) of deep-gas generation than that predicted by the 

composite-pyrolysis model (0-7 mg/g C). The hydrous-pyrolysis model for only Type-II 

kerogen yields no deep gas at the high heating rate and 23 mg/g C of deep gas at the slow 

heating rate. Obviously, more hydrous-pyrolysis kinetic studies on the other kerogen 

types are needed.

It would be valuable to compare all the different kerogen types for the three 

pyrolysis models, but a complete comparison of kerogen types is only possible between
the open- and composite-pyrolysis models. At both heating rates, the open-pyrolysis 

model predicts an increase in the amount of deep gag generated from Type-I to Type-II to 

Type-Ill kerogen. With the exception of Type-US kerogen, this trend is also predicted by 

the composite-pyrolysis model (i.e., Type-I < Type-II < Type-Ill kerogen). Tlie 

composite-pyrolysis method predicts that Type-IIS kerogen generates the least amount of 

deep gas at both heating rates. The implication of this prediction is that deep basins with 

high-sulfur oils and carbonate source rocks are not good prospects for deep gar. 

However, in the open-pyrolysis model, type US kerogen generates about the same amount 

of deep gas as Type-II kerogen at both heating rates.

For the slow heating rate, the composite-pyrolysis model predicts more deep g?** 

generation than the open-pyrolysis model for all kerogen types except for Type-IIS 

kerogen. As an example, three times as much deep-gas generation is predicted by TypeII kerogen in the composite-pyrolysis model than in the open-pyrolysis model. The 

hydrous-pyrolysis model for deep-gas generation from Type-II kerogen predicts an 

intermediate value (23 mg/g C) at the low heating rate and the lowest value (0 mg/g C) at 

the high heating rate relative to the predictions by the composite- and open-pyrolysis 

models. Type-II kerogen is the most common source of oil and the results presented 

here (Table 7) suggest that the predicted potential for deep gas from this kerogen type is 

highly dependent on the pyrolysis model employed.

Type-I kerogen, which is typically associated with lacustrine sequences and 

source rocks, consistently has low yields of deep-gas generation in both open- and 

composite-pyrolysis models and at both heating rates (Table 7). These predictions 

suggest that basins with deeply buried lacustrine source rock sequences are not favorable 

for deep-gas generation from kerogen. Conversely, Type III kerogen produces more 

deep gas than the other kerogen types in both the open- and composite-pyrolysis models 

and for both heating rates. These predictions imply that basins with deeply buried coals 

are the most favorable for deep-gas generation from kerogen.

Oil to Gas

Deep gas from the cracking of oil retained in a source rock does not depend on 

kerogen type or lithology according to the anhydrous-pyrolysis model by Pepper and 

Dodd (1995). Similar to deep-gas generation from kerogen, deep gas from retained oil in 

source rocks is most favorable at low heating rates (Table 8). At l°C/m.y., this mode? 

predicts amounts of deep-gas generation that are comparable to those predicted by th? 

composite-pyrolysis model for deep-gas generation from Type-II and -III kerogens (Table 

8). At the high heating rate, no deep-gas generation from the cracking of retained oil in 

source rocks is predicted (Table 8). Therefore, at 10°C/m.y., deep-gas generation from 

kerogen is more favorable than from the retained oil in a source rock.

Anhydrous- and hydrous-pyrolysis models predict that amounts of deep-ga? 

generated from the cracking of reservoir oil are four- to seven-times greater at l°C/m.y. 

and six- to twenty-times greater at 10°C/m.y. than the best deep-gas yields obtained from 

kerogen (Table 7). This difference is readily explained by oil having a higher thermal 

stability than kerogen. It has also been shown that the thermal stability of oil increases in 

the presence of liquid water (Hesp and Rigby, 1973), which would be ubiquitous in most

10
subsurface reservoirs. This increase in stability with water is supported in part by the 

lower deep-gas yields predicted by the hydrous-pyrolysis model than anhydrouspyrolysis model at the high heating rate (Table 6). Although the deep-gas yields 

predicted for the cracking of reservoir oil are considerably higher than those for kerogen, 

the amount of kerogen in deeply buried source rocks of a sedimentary basin may b°< 

several orders of magnitude greater than the amounts of deeply buried reservoir oil.

CONCLUSIONS AND FUTURE STUDIES

1. Basins with slow heating rates, where source rocks subside slowly through low thermal 

gradients, are more likely to yield deep gas from kerogen than basins with fast heating 

rates and rapid subsidence of source rock. Because this is one of the most important 

implications of this study, it would be interesting to compare amounts of deep gas and 

heating rates from different sedimentary basins. This would involve creating an inventor' 

of heating rates for domestic basins as well as the amount of deep gas recovered to date. 

A future study of this type can be used to evaluate the validity of the different models 

used in this study and target basins with high potential for deep gas.

2. According to the open- and composite-pyrolysis models, Type-Ill kerogen will yield 

the most deep gas of the three kerogen types irrespective of heating rate. This implie^ 

that basins with deeply buried coals are most likely to contain deep gas. A future study 

comparing deep-gas yields from basins with differing amounts of deeply buried coal 

would be a useful way of testing this model-based prediction and targeting basins with 

high potential for deep gas.

3. According to the open- and composite-pyrolysis models, Type-I kerogen has the least 

or no potential for deep-gas generation. This implies that basins with deeply buried 

lacustrine source rocks are not likely to contain deep gas. A future study comparing 

deep-gas yields from basins with differing amounts of deeply-buried lacustrine source 

rocks would be a useful way of testing this model-based prediction and exclude basin? 

with low potential for deep gas.

4. Cracking of reservoir oil is predicted by the anhydrous- and hydrous-pyrolysis models 

to generate the most deep gas irrespective of heating rate. Therefore, basins that currently 

have deeply buried overmature source rocks have the potential of previously having 

reservoir oil that has since cracked to generate deep gas. The main control for deep-ga^ 

accumulations in this geological setting is the original oil trap remaining competent with 

burial depth. The Gulf Coast offshore and the Anadarko basin may serve as examples of 

this geological setting. Future studies of these types of basins can further elucidate the 

factors controlling deep-gas accumulations and target other areas with high potential for 

deep gas.

5. There are not significant differences between the predicted amount of deep-ga^ 

generated from kerogen by the different pyrolysis kinetic models. However, the hydrouspyrolysis model considers only Type-II kerogen, and more hydrous-pyrolysis

11
experiments with kinetic models for gas generation from Type-I, Type-US, and Type-Ill 

kerogens are needed to test this preliminary conclusion.

6. There is a significant difference between the predicted amounts of deep-gas generated 

from the cracking of reservoir oil by the anhydrous- and hydrous-pyrolysis kinetic 

models. The kinetic model derived-from hydrous pyrolysis indicates that reservoir oil is 

more thermally stable and that oil cracking to gas requires higher thermal stress leve's 

than those predicted by the anhydrous-pyrolysis model. More experimental work on the 

cracking of oil in the presence of water is needed. In addition, these future experiments 

need to consider the effects of commonly occurring reservoir minerals and their surface". 

Experiments published to date on the cracking of reservoir oil have neglected the 

potential effects of minerals on gas generation.

ACKNOWLEDGEMENTS

This study was funded in part by the U. S. Department of Energy (Federal Energy 

Technology Center, Morgantown, WV, contract no. DE-AT26-98FT40032), G?s 

Research Institute (Chicago, IL) as a Cooperative Research and Development Agreement 

with Advanced Resources International (Arlington, VA), and the Central Energy Team cf 

the U. S. Geological Survey (Denver, CO). The authors also appreciate the helpful 

reviews of this report made by John Curtis (Colorado School of Mines), Thaddeus 

Dyman (USGS), and Katherine Vames (USGS).

REFERENCES

Behar, F. and Vandenbroucke, M., 1996, Experimental determination of the rate

constants of the n-C25 thermal cracking at 120, 400, and 800 bar: Implications 

for high-pressure/high-temperature prospects: Energy & Fuels 10, 932-940.

Behar, F., Vandenbroucke, M., Tang, Y., Marquis, F. and Espitalie, J., 1997, Thermal 

cracking of kerogen in open and closed systems: determination of kinetic 

parameters and stoichiometric coefficients for oil and gas generation: Org. 

Geochem. 26, p. 321-339.

Braum, R. L. and Burnham, A. K., 1987, Analysis of chemical reactions using a

distribution of activation energies and simpler models: Energy & Fuel 1, pp. 153- 

161.

Burnham, A.K., Gregg, H.R., Ward, R.L., Knauss, K.G., Copenhaver, S.A., Reynolds, 

J.G., Sanborn, R., 1997, Decomposition kinetics and mechanism of «- 

hexadecane-l,2-' 3C2 and dodec-l-ene-l,2-' 3C2 doped in petroleum and nhexadecane: Geochimica et Cosmochimica Acta 61, pp. 3725-3737.

Domine, F., 1991, High pressure pyrolysis of H-hexane, 2,4-dimethylpentane and 1-

phenylbutane. Is pressure an important geochemical parameter? Org. Geochem. 

17, pp. 619-634.

12
Dyman, T. S., Rice, D. D., and Westcott, P. A., 1997, Introduction in Dyman, T. S., Rice, 

D. D., and Westcott, P. A., eds., Geological controls of deep natural gas 

resources in the United States: U. S. Geological Survey Bulletin 2146, p. 3-5.

Gorbachev, V. M., 1975, A solution to the exponential integral in the non-isothermal 

kinetics for linear heating: Journal of Thermal Analysis 6, p. 349-350.

Gretener, P.E. and Curtis, C.D., 1982, Role of temperature and time on organic 

metamorphism Am. Assoc. Petrol. Geol. Bull. 66, p. 1124-1129

Hesp , W. and Rigby, D., 1973, The geochemical alteration of hydrocarbons in the

presence of water: Erdol Kohle-Ergas-Petrochem. Brennstoff-Chemie 26, p. 70- 

76.

Horsfield, B., Schenk, H.J., Mills, N. and Welte, D.H., 1992, An investigation of the inreservoir conversion of oil to gas: compositional and kinetic findings from closedsystem programmed-temperature pyrolysis Advances in Organic Geochemistry, 

19, p. 191-204

Jamil, A.S.A., Anwar, M.L. and Kiang, E.S.P., 1991, Geochemistry of selected crude 

oils from Sabah and Sarawak Geol. Soc. Malaysia Bull. 28, p. 123-149

Knauss, K.G., Copenliaver, S.A., Braun, R.L. and Burnham, A.K., 1997, Hydrous 

pyrolysis of New Albany and Phosphoria Shales: production kinetics of 

carboxylic acids and light hydrocarbons and interactions between, the inorganic 

and organic chemical systems Org. Geochem. 27, p. 477-496.

Pepper, A.S. and Corvi, P.J., 1995, Simple kinetic models of petroleum formation.

Part I: Oil and gas generation from kerogen Mar. Petrol. Geol. 12, p. 291-319

Pepper, A.S. and Dodd, T.A., 1995, Simple kinetic models of petroleum formation. 

Part II: Oil-gas cracking Mar. Petrol. Geol. 12, p. 321-340

Price, L. C., 1997, Origins, characteristics, evidence for and economic viabilities of

conventional and unconventional gas resource bases: in Dyman, T. S., Rice, D. 

D., and Westcott, P. A., eds., Geological controls of deep natural gas resources in 

the United States: U. S. Geological Survey Bulletin 2146, p. 181-207.

Tsuzuki, N., Yokoyama, Y., Takayama, K., Yokoi, K., Suzuki, M. and Takeda, N.

Kinetic modeling of oil cracking, 1997 Eastern Section American Association 

of Petroleum Geologists and The Society of Organic Petrology Joint Meeting: 

Lexington, Kentucky; Abstracts and Program, Volume 14, 94-96

Ungerer, P., Espitalie, J, Marquis, F., and Durand, B., 1986, Use of kinetic models of

organic matter evolution for the reconstruction of paleotemperatures: in Burruss,

13
J., ed., Thermal Modeling in Sedimentary Basins: Paris, Editions Technip., p. 

531-546.

Wood, D. A., 1988, Relationships between thermal maturation indices calculated using 

Arrhenius equation and Lopatin method: Implications for petroleum exploration: 

American Association of Petroleum Geologists Bulletin 72, 115-134.

14
Table 1: Summary of six gas-generation kinetic models considered in this study.

MODEL NAME REF* STARTING MATERIAL

Open Pyrolysis 

Composite Pyrolysis 

Hydrous Pyrolysis

Anhydrous Pyrolysis

Kerogen 

(Type-1,-11, US, III)

Kerogen 

(Type-1,-11, US, III)

Crude 

(Type-II)

Kerogen 

Oil 

(light and heavy saturates)

Crude Oil 

(36°API gravity)

Immature Source Rock 

(Organofacies A, B, C, D/E, F)

KINETIC APPROACH

Optimization of non-isothermal 

experiments at different heating rates

Optimization of open and 

anhydrous pyrolysis and natural data

Optimization of isothermal pyrolysis 

experiments

Optimization of isothermal pyrolysis 

experiments

Optimization of non-isothermal 

experiments at different heating rates

Optimization of isothermal pyrolysis 

experiments at one temperature

KINETIC PA

Discrete distribu

energies with sing

Gaussian distribu

energies with sing

Gaussian distribu

energies with sing

Single activation ene

factors for light a

Discrete distribu

energies with sing

Gaussian distribu

energies with sing

* References: 1 = Behar and others (1997); 2 = Pepper and Corvi (1995); 3 = Knauss and others (1997); 4 = Tsuzuki and oth

5 = Horsficld and others (1992); 6 = Pepper and Dodd (1995)
Table 2: Fractional gas yields assigned to discrete activation energies and single frequency factors used by Behar 

to model gas generation from kerogen.

Type-I Kerogen

Activation

Energy (kcal/mol)

74.0

72.0

70.0

68.0

66.0

64.0

62.0

60.0

58.0

56.0

54.0

52.0

50.0

48.0

46.0

44.0

c,

Fractional

Gas Yield

0.00

0.00

0.00

0.00

0.02

0.08

0.08

0.10

0.12

0.19

0.38

0.02 .

0.00

0.00

0.00

0.00

C2-C5

Fractional

Gas Yield

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.95

0.05

0.00

0.00

0.00

0.00

FRACTIONAL PART OF TOTAL GAS YIELD 

Type-IJ Kerogen Tvpe-IIS Kerogen Tvpe-III

Ci

Fractional

Gas Yield

0.00

0.00

0.00

0.00

0.02

0.07

0.11

0.13 .

0.19

0.15

0.15

0.11

0.05

0.02

0.00

0.00

C2-C5

Fractional

Gas Yield

 o.oo

0.00

0.00

0.002

0.006

0.014

0.024

0.040

0.092

0.225

0.247

0.241

0.092

0.016

0.002

0.00

Ci

Fractional

Gas Yield

0.00

0.00

0.00

0.00

0.004

0.019

0.034

0.174

.0.159

0.186

0.144

0.080

0.080

0.068

0.042

0.011

C2-C5

Fractional

Gas Yield

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.01

0.03

0.05

0.19

0.27

0.16

0.21

0.06

0.01

Ci

Fractional

Gas Yield

O.OQ

0.02

0.13

0.16

0.16

0.16

0.14

0.11

0.07

0.03

0.01

0.00

0.00

0.00

0.00

0.00

' Kerogen

C2-C5

Fractional

Gas Yield

0.00

0.00

0.00

0.02

0.04

0.07

0.17

0.28

0.22

0.13

0.05

0.02

0.01

0.00

0.00

0.00

Frequency 2.33E+27 2.33E+27 5.05E+27 5.05E+27 7.88E+26 7.88E+26 9.46E+28 9.46E+28 

Factor (1/m.y.)

Total gas yields 16.4mg/gC 72.1mg/gC 18.8mg/gC 50.2 mg/g C 26.4mg/gC 43.9mg/gC 30.6mg/gC 23.6mg/g
Table 3: Fractional CrC4 gas yields 

assigned to discrete activation energies 

by Horsfield and others (1992) to model 

gas generation from the cracking of oil.

Activation

Energy (kcal/mol)

73

72

70

69

68

67

66

63

58

55

54 .

53

51

50

Fractional

Gas Yields

0.0174

0.0087

0.0587

0.1109

0.1478

0.2870

0.3435

0.0043

0.0065

0.0022

0.0022

0.0043

0.0022

0.0022

Frequency 

Factor (l/m.y.)

Total gas yield

3.47E+29

460 mg/g Oil

17
Table 4a: Gaussian distributions and their calculated discrete distributions of activation 

energies with fractional C,-C5 gas yields from kerogens as predicted by the composite 

pyrolysis model (Pepper and Corvi, 1995).

Organofacies A 

Type US 

Gaussian Distribution

of Activation Energies

(kcal/mol)

mean

std.dev.

49.4

2.6

Discrete Distribution

Activation

Energies

(kcal/mol)

56.4

55.4

54.4

53.4

52.4

51.4

50.4

49.4

48.4

47^4

46.4

45.4

44.4

43.4 .

42.4

41.5

40.5

39.5

38.5

37.5

36.5

35.5

34.5

Frequency

Factor

(1/m.y.)

Fractional

Gas Yield

0.0037

0.0100

0.0231

0.0460

0.0785

0.1150

0.1446

0.1560

0.1445

0.1148

0.0783

0.0458

0.0230

0.0099

0.0037

0.0000

0.0000

0.0000

0.0000

0.0000

0.0000

0.0000

0.0000

1.24E+26

Organofacies B 

Type II 

Gaussian Distribution

of Activation Energies

(kcal/mol)

mean

std.dev.

66.6

4.4

Discrete Distribution

Activation

Energies

(kcal/mol) '

77.6

76.6

75.6

74.6

73.6

72.6

71.6

70.6

69.6

68.6

67.6

66.6

65.6

64.6

63.6

62.6

61.6

60.6

59.6

58.6

57.6

56.6

55.6

Fractional

Gas Yield

0.0040

0.0069

0.0112

0.0174

0.0257

0.0359

0.0477

0.0601

0.0720

0.0819

0.0885

0.0907

0.0884

0.0817

0.0718

0.0598

0.0474

0.0356

0.0255

0.0173

0.0111

0.0068

0.0039

6.84E+31

Organofacies C 

Type I 

Gaussian Distribution

of Activation Energies

(kcal/mol)

mean

std.dev.

59.8

2.4

Discrete Distribution

Activation

Energies

(kcal/mol)

65.8

64.8

63.8

62.8

61.8

60.8

59.8

58.8

57.8

56.8

55.8

54.8

53.8

52.8

51.8 -

. 50.8

49.8

48.8

47.8

46.8

45.8

44.8

43.8

Fractional

' Gas Yield

0.0079

0.0201

0.0432

0.0782

0.1191

0.1529

0.1652

0.1504

0.1154

0.0745

0.0405

0.0186

0.0072

0.0000

0.0000

0.0000

0.0000

0.0000

0.0000

0.0000

0.0000

0.0000

0.0000

7.22E+29

Organofacies F/DE 

Type Ill/Ill' 

Gaussian Distribution

of Activation Energies

(kcal/mol)

mean

std.dev.

65.7

2.4

Discrete Distribution

Activation

Energies

(kcal/mol)

71.7

70.7

69.7

68.7

67.7

66.7

65.7

64.7

63.7

62.7

. 61.7

60.7

59.7

58.7

57.7

56.7

55.7

54.7

53.7

52.7

51.7

50.7

49.7

Fractional

Gas Yield

0.0070

0.0185

0.0412

0.0766

0.1191

0.1549

0.1686

0.1535

0.1168

0.0744

0.0396

0.0177

0.0066

0.0000

0.0000

0.0000

0.0000

0.0000

0.0000

0.0000

0.0000

0.0000

0.0000

6.09E+29

18
Table 4b: Gaussian distributions and their calculated discrete distributions of activation energies with fractio

from oil retained in mature source rocks as predicted by the anhydrous pyrolysis model (Pepper and Dodd, 19

factor (1/m.y.) for all source rocks is 3.15 x 10". Source rock abbreviations are given in caption of Figure 6.

Source Rock BL SM

Gaussian Distribution

Activation Energies (kcal/mol)

mean

std. dev.

58.7 57.7

1.7 2.9

Discrete Distribution

Activation

Energy

(kcal/mol)

65.7

64.7

63.7

62.7

61.7

60.7

59.7

58.7

57.7

56.7

55.7

54.7

53.7

52.7

51.7

50.7

49.7

48.7

47.7

46.7

45.7

44.7

Fractional

Gas Yield

0.0000 0^0030

0.0000 0.0073

0.0026 0.0161

0.0132 0.0313

0.0466 0.0537

0.1147 0.0818

0.1977 0.1102

0.2384 0.1316

0.2011 0.1391

0.1187 0.1302

0.0490 0.1079

0.0142 0.0792

0.0029 0.0515

0.0000 0.0296

0.0000 0.0151

0.0000 0.0068

0.0000 0.0027

0.0000 0.0000

0.0000 0.0000

0.0000 0.0000

0.0000 0.0000

0.0000 0.0000

Source Rock AWD Ha Source Rock

Gaussian Distribution

Activation

mean

std. dev.

Energies (kcal/mol)

58.4 56.4

2.4 3.6

mean

std. dev.

Discrete Distribution

Activation

Energy

(kcal/mol)

68.4

67.4

66.4

65.4

64.4

63.4

62.4

61.4

60.4

59.4

58.4

57.4

56.4

55.4

54.4

53.4

52.4

51.4

50.4

49.4

48.4

47.4

Fractional

Gas Yield

0.0000 0.0000

0.0000 0.0000

0.0000 0.0000

0.0022 0.0048

0.0069 0.0093

0.0182 0.0166

0.0401 0.0275

0.0745 0.0422

0.1162 0.0598

0.1520 0.0785

0.1669 0.0953

0.1538 0.1071

0.1190 0.1113

0.0773 0.1070

0.0422 0.0952

0.0193 0.0783

0.0074 0.0596

0.0024 0.0420

0.0000 0.0274

0.0000 0.0 165

0.0000 0.0092

0.0000 0.0047

Activation

Energy

(kcal/mol)

68.1

67.1

66.1

65.1

64.1

63.1

62.1

61.

60.

59.

58.

57.

56.

55.

54.1

53.1

52.1

51.1

50.1

49.1

48.1

47.1

PAL LC9 

Gaussian Distr

Activation

58.1

2.2

Energie

57.1 

3.6 

Discrete Distributio

0.0000

0.0000

0.0000

0.0000

0.0037

0.0122

0.0323

0.0691

0.1193

0.1657

0.1855

0.1672

0.1215

0.0711

0.0335

0.0127

0.0039

0.0000

0.0000

0.0000

0.0000

0.0000

Frac

Gas 

0.0000 

0.0022 

0.0046 

0.0089 

0.0161 

0.0268 

0.0413 

0.0588 

0.0775 

0.0945 

0.1066 

0.1113 

0.1074 

0.0960 

0.0793 

0.0606 

0.0429 

0.0281 

0.0170 

0.0095 

0.0049 

0.0024 
Table 4b: (Continued)

NJ

O

Source Rock LC1

Gaussian Distribution

Tu

Activation Energies (kcal/mol) 

mean 57.3 58.3 

std. dev. 2.9 2.4

Discrete Distribution

Activation 

Energy

(kcal/mol)

68.3

67.3

66.3

65.3

64.3

63.3

62.3

61.3

60.3

59.3

58.3

57.3

56.3

55.3

54.3

53.3

52.3

51.3

50.3

49.3

48.3

47.3

46.3

Fractional

Gas Yield

0.0000

0.0000

0.0000

0.0028

0.0069

0.0152

0.0298

0.0517

0.0795

0.1082

0.1303

0.1391

0.1314

0.1100

0.0815

0.0535

0.03 1 1

0.0160

0.0073

0.0029

0.0000

0.0000

0.0000

0.0000

0.0000

0.0000

0.0023

0.0073

0.0190

0.0416

0.0766

0.1183

0.1534

0.1669

0.1525

0.1169

0.0752

0.0406

0.0184

0.0070

0.0022

0.0000

0.0000

0.0000

0.0000

0.0000

mean 

std. dev.

Activation 

Energy

(kcal/mol)

68.6

67.6

66.6

65.6

64.6

63.6

62.6

61.6

60.6

59.6

58.6

57.6

56.6

55.6

54.6

53.6

52.6

51.6

50.6

49.6

48.6

47.6

46.6

GA

56.6 

4.8

KFC P5 Maui

Gaussian Distribution

Activation Energies (kcal/mol) 

58.6 58.6 57.6 

2.6 1.9 3.6

Discrete Distribution

WE 

G

Activa

57.6 

4.3 

D

Fractional

Gas Yield

0.0037

0.0060

0.0095

0.0144

, 0.0209

0.0290

0.0384

0.0488

0.0593

0.0689

0.0768

0.0818

0.0835

0.0815

0.0762

0.0681

0.0583

0.0478

0.0375

0.0282

0.0203

0.0139

0.0092

0.0000

0.0000

0.0000

0.0042

0.0108

0.0241

0.0465

0.0776

0.1122

0.1402

0.1517

0.1420

0.1150

0.0806

0.0489

0.0257

0.0117

0.0046

0.0000

0.0000

0.0000

0.0000

0.0000

0.0000

0.0000

0.0000

0.0000

0.0014

0.0064

0.0223

0.0588

0.1179

0.1798

0.2086

0.1841

0.1236

0.0631

0.0245

0.0072

0.0016

0.0000

0.0000

0.0000

0.0000

0.0000

0.0000

0.0000

0.0023

0.0048

0.0092

0.0165

0.0274

0.0421

0.059

0.0784

0.0952

0.107

0.1113

0.1070

0.0952

0.0784

0.0597

0.0421

0.0274

0.0165

0.0092

0.0048

0.0023

0.0000

0.0035

0.0062

0.0104

0.0165

0.0247

0.0351

0.0472

0.0602

0.0727

0.0832

0.0903

0.0927

0.0903

0.0832

0.0727

0.0602

0.0472

0.0351

0.0247

0.0165

0.0104

0.0062

0.0035

A

(k
Table 4c: Gaussian distributions and their calculated discrete distributions of activation 

energies with fractional methane (Ci), ethane (C2), propane ( 3), and butane ( 4) yields 

from Type-II kerogen in the New Albany Shale (Devonian-Mississippian) as predicted 

by the hydrous-pyrolysis model (Knauss and others, 1997).

Methane (C,)

Gaussian Distribution

E (kcal/mol)

std. dev.(%E)

45.2

1.92

Discrete Distributon

Activation

Energies

(kcal/mol)

65.4

64.4

63.4

62.4

61.4

60.4

59.4

58.4

57.4 '

56.4

55.4

54.4

53.4

52.4

51.4

50.4

49.4

48.4

47.4

46.4

45.4

44.4

43.4

42.4

Frequency

Factor (1/m.y.)

Fractional

Gas Yield

0.0000

0.0000

0.0000

0.0000

0.0000

0.0000

0.0000

, 0.0000

0.0000

0.0000

0.0000

0.0000

0.0000

0.0000

0.0000

0.0000

0.0000

0.0012

0.0329

0.2370

0.4577

0.2370

0.0329

0.0012

7.88E+23

Ethane (C2)

Gaussian Distribution

E (kcal/mol)

std. dev.(%E)

56.2

5.0

Discrete Distributon

Activation

Energies

(kcal/mol)

65.2

64.2

63.2

62.2

61.2

60.2

-59.2

58.2

57.2

56.2

55.2

54.2

53.2

52.2

51.2

50.2

49.2

48.2

47.2

46.2

45.2

44.2

43.2

42.2

Fractional

Gas Yield

0.0008

0.0025

0.0064

0.0145

0.0292

0.0515

0.0803

0.1102

0.1333

0.1420

0.1333

0.1102

0.0803

0.0515

0.0292

0.0145

0.0064

0.0025

0.0008

0.0000

0.0000

0.0000

0.0000

0.0000

1.23E+28

Propane (C3)

Gaussian Distribution

E (kcal/mol)

std. dev.(%E)

52.9

6.0

Discrete Distributon

Activation

Energies

(kcal/mol)

64.9

63.9

62.9

61.9

60.9

59.9

58.9

57.9

56.9

55.9

54.9

53.9

52.9

51.9

50.9

49.9

48.9

47.9

46.9

45.9

44.9

43.9

42.9

41.9

Fractional

Gas Yield

0.0000

0.0000

0.0009

0.0023

0.0052

0.0110

0.0211

0.0363

0.0568

0.0804

0.1031

0.1196

0.1257

0.1196

0.1031

0.0804

0.0568

0.0363

0.0211

0.0110

0.0052

0.0023

0.0009

0.0000

5.68E+26

Butane (C4)

Gaussian Distribution

E (kcal/mol)

std. dev.(%E)

55.0

5.0

Discrete Distributon

Activation

Energies

(kcal/mol)

65.0

64.0

63.0

62.0

61.0

60.0

59.0

58.0

57.0

56.0

55.0

54.0

53.0

52.0

51.0

50.0

49.0

48.0

47.0

46.0

45.0

44.0

43.0

42.0

Fractional

Gas Yield

0.0000

0.0007

0.0021

0.0057

0.0134

0.0278

0.0504

0.0800

0.1114

0.1358

0.1451

0.1358

0.1114

0.0800

0.0504

0.0278

0.0134

0.0057

0.0021

0.0007

0.0000

0.0000

0.0000

0.0000

3.15E+27

21
Table 5: Maximum CrC5 gas yields 

for different starting materials used in 

six kinetic models.

Starting Material Model . Maximum 

Reference* Gas Yield 

(mg/gC)

Type-I Kerogen

Type-II Kerogen

Type-IIS Kerogen

Type-IE Kerogen

Type-Ill' Kerogen

Source-Rock Oil

Reservoir Oil

1

2

1

2

3

1

2

1

2

1

2

4

5

(mg/gOil)

6

(mg/gOil)

88.5

78.0

70.0

100.6

92.8**

70.3

104.9

57.1

76.6

54.2

69.5

100.00

541.2

(460.0)

376.2

(319.8)

* References: 1 = Behar and others (1997)

2 = Pepper and Corvi (1995)

3 = Knauss and others (1997)

4 = Pepper and Dodd (1995)

5 = Horsfield and others (1992)

6 = Tsuzuki and others (1997) 

**CrC4

22
Table 6: Summary of gas generation-curves for kerogens and oils (Figures 1-6) with respect to yield, depth, time, and temperature for 

of 0.05, 0.25, 0.50, 0.75,and 0.99 at 1 and 10°C/m.y. heating rates for each kinetic model. Last column of each heating rate gives the f

time, and temperature at the start of deep gas (15,OOOft/4,572 m).

Type-1 Kerogen

Open-Pyro lysis Model'1 '

Fraction of Reaction (X)

Gas Yield (mg/g C)

(ft'/kg C)

Depth (m)

Time (m.y.)

Temperature ("C)

Composite-Pyrolysis Modelpl

Fraction of Reaction (X)

Gas Yield (mg/g C)

(ft'/kg C)

Depth (m)

Time (m.y.)

Temperature (-Q

Type-II Kerogen

Open-Pyrolysis Model1 ' 1

Fraction of Reaction (X)

Gas Yield (mg/g C)

(ft'/kg C)

Depth (m)

Time (m.y.)

Temperature (-Q

Composite-Pyrolysis Moder '

Fraction of Reaction (X)

Gas Yield (mg/g C)

(ft'/kg C)

Depth (m)

Time (m.y.)

Temperature (-C)

Hydrous-Pyrolysis Model131

Fraction of Reaction (X)

Gas Yield (mg/g C)

(ft'/kg C)

Depth (m)

Time (m.y.)

Temperature ("C)

0.050

4

0.168

3600

108

128

0.050

4

0.149

3400

102

122

0.050

4

0.134

2800

84

104

0.050

5

0.191

3400

102

122

0.050

5

0.180

2800

84

104

0.250

22

0.840

4000

120

140

0.250

20

0.744

4000

120

140

0.250

18

0.668

3600

108

128

0.250

25

0.954

4400

132

152

0.250

23

0.899

3400

102

122

-l°C/m.y. -

0.500

44

1.680

4200

126

146

0.500

39

1.489

4400

132

152

0.500

35

1.336

4200

126

146

0.500

50

1.909

5000

150

170

0.500

47

1.797

3800

114

134

0.750

66

2.520

4200

126

146

0.750

59

2.233

4800

144

164

0.750

53

2.004

4800

144

164

0.750

75

2.863

5600

168

188

0.750

70

2.696

4572

137

157

0.990

. . 87

3.326

6800

204

224

0.990

77

2.948

5600

168

188

0.990

69

2.645

6800

204

224

0.990

99

3.779

7200

216

236

0.990

92

3.559

5800

174

194

0.909

80

3.054

4572

137

157

0.641

78

2.978

4572

137

157

0.671

47

1.794

4572

137

157

0.350

35

1.336

4572

137

157

0.753

70

2.706

4572

137

157

0.050

4

0.168

2400

11

128

0.050

4

0.149

2400

11

128

0.050

4

0.134

1800

8

101

0.050

5

0.191

2400

11

128

0.050

5

0.180

2000

9

110

0.250

22

0.840

2600

12

137

0.250

20

0.744

2600

12

137

0.250

18

0.668

2400

11

128

0.250

25

0.954

3000

14

155

0.250

23

0.899

2400

11

128

~10°

0.5

1.6

28

1

0.5

1.4

30

1

0.5

1.3

28

1

0.5

1.9

34

1

0.5

1.7

28
Table 6 (continued)

Type-IIS Kerogen

Open-Pyrolysis Model^' 1

Fraction of Reaction (X)

Gas Yield (mg/g C)

(ftVkg C)

Depth (m)

Time (m.y.)

Temperature (-C)

Composite-Pyrolysis Model^2'

Fraction of Reaction (X)

Gas Yield (mg/g C)

(ft'/kg C)

Depth (m)

Time (m.y.)

Temperature ("C)

Type-Ill Kerogen

Open-Pyrolysis ModeF1

Fraction of Reaction (X)

Gas Yield (mg/g C)

(ft'/kg C)

Depth (m)

Time (m.y.)

Temperature ("C)

Composiie-Pyrolysis Model^2 '

Fraction of Reaction (X)

Gas Yield (mg/g Q

(ft'/kg C)

Depth (m)

Time (m.y.)

Temperature ("C)

Type-Ill1 Kerogen

Open-Pyrolysis Modelfl1

Fraction of Reaction (X)

Gas Yield (mg/g C)

(ft'/kg C)

Depth (m)

Time (m.y.)

Temperature (-Q

0.050

4

0.134

2400

72

92

0.050

5

0.200

2400

72

92

0.050

3

0.000103

3600

108

128

0.050

4

0.145

4800

144

164

0.050

3

0.109

4200

126

146

0.250

18

0.668

3000

90

110

0.250

26

1.002

3000

90

110

0.250

14

0.000515

4400

132

152

0.250

19

0.725

5400

162

182

0.250

14

0.544

5000

150

170

 l°C/m.y,

 0.500

35

1.336

4000

120

140

0.500

53

2.004

3400

102

122

0.500

27

0.001031

5200

156

176

0.500

38

1.451

5800

174

194

0.500

29

1.088

5800

174

194

0.750

53

2.004

4572

137

157

0.750

79

3.006

4000

120

140

0.750

41

0.001546

6200

186

206

0.750

57

2.176

6000

180

200

0.750

43

1.632

6600

198

218

0.990

69

2.645

6400

192

212

0.990

104

3.968

5000

150

170

0.990

53

0.002041

7400

222

242

0.990

75

2.872

7000

210

230

0.990

56

2.154

7800

234

254

0.743

52

1.985

4572

137

157

0.933

98

3.741

4572

137

157

0.259

14

0.000534

4572

137

157

0.026

2

0.076

4572

137

157

0.105

6

0.229

4572

137

157

in°/

0.050

4

0.134

1600

7

92

0.050

5

0.200

1600

7

92

0.050

3

0.000103

2400

11

128

0.050

4

0.145

3200

14

164

0.050

3

0.109

3000

14

155

0.250

18

0.668

2200

10

119

0.250

26

1.002

2000

9

110

0.250

14

0.000515

3200

14

164

0.250

19

0.725

3600

16

182

0.250

14

0.544

3400

15

173

0.5

1.3

28

1

0.5

2.0

24

1

0.5

0.0010

36

1

0.5

1.4

40

2

0.5

1.0

40

2
Table 6 (continued)

Type-Ill 1 Kerogen

Composite-Pyrolysis Modelf2J

Fraction of Reaction (X)

Gas Yield (mg/g C)

(ftVkg C)

Depth (m)

Time (m.y.)

Temperature (-C)

Oil in Source Rock

Anhydrous-Pyrolysis Model^

Fraction of Reaction (X)

Gas Yield (mg/g C)

(ftVkg C)

Depth (m)

Time (m.y.)

Temperature (-C)

Oil in Reservoirs

Anhydrous-Pyrolysis Model^ *

Fraction of Reaction (X)

Gas Yield (mg/g Oil)

(ftVkg Oil)

Depth (m)

Time (m.y.)

Temperature ('Q

Anhydrous-Pyrolysis Model1*1

Fraction of Reaction (X)

Gas Yield (mg/g Oil)

(ftVkg Oil)

Depth (m)

Time (m.y.)

Temperature ('Q

0.050

4

0.134

4600

138

158

0.050

5

0.191

3600

108

128

0.050

23

0.889

5400

162

182

0.050

16

0.000611

5800

174

194

0.250

18

0.668

5400

162

182

0.250

25

0.954

4400

132

152

0.250

115

4.445

6000

180

200

0.250

80

0.003054

6200

186

206

 l°C/m.y,

0.500

35

1.336

5800

174

194

0.500

50

1.909

5000

150

170

0.500

230

8.890

6200

186

206

0.500

160

0.006108

6400

192

212

0.750

53

2.004

6000

180

200

0.750

75

2.863

5400

162

182

0.750

345

13.336

6400

192

212

0.750

240

0.009162

7200

216

236

0.990

69

2.645

. 7000

210

230

0.990

99

3.779

6600

198

218

0.990 at

455

17.603

7600

228

248

0.990

317

0.012094

7400

222

242

0.029

2

0.076

4572

137

157

0.353

35

1.347

4572

137

157

15,000 ft

0.022

0.001

4572

137

157

0.000

0.000

0.000

4572

137

157

0.050

4

0.134

3200

14

164

0.050

5

0.191

2400

11

128

0.050

23

0.889

3800

17

191

0.050

16

0.000611

4000

18

200

0.250

18

0.668

3600

16

182

0.250

25

0.954

3000

14

155

0.250

115

4.445

4000

18

200

0.250

80

0.003054

4200

19

209

 10°

0.5

1.3

40

2

0.5

1.9

34

1

0.5

2

8.8

42

2

0.5

1

0.0061

44

2

mBehar and others (1997); [2]Pepper and Corvi (1995); [11Knauss and others (1997); ^Pepper and Dodd (1995) 

t5]Horsfield and others (1992); [61Tsuzuki and others (1997)
Table 7: Amounts of gas generated from kerogen above and below the deep-gas depth of 4,572 

(15,000 ft). All values refer to CrC5 gas, except where otherwise noted.

Kinetic Model

Open Pyrolysis*1 '

Composite Pyrolysis1 '

Hydrous Pyrolysis^31

Kerogen

Type

Type I

Type II

Type US

Type III

Type IIP

Type I

Type II

Type US

Type III

Type IllType II

I T/mvGas Generated

Above 4572 m

(mg/gC)

80

50

50

6

14

50

35

100

2

2

70*

Below 4572 m

(mg/gC)

8

20

20

51

40

28

65

5

75

68

23*

1 0 T/mv

Gas Generated

Above 4572 m

(mg/g C)

87

68

69

42

46

78

95

105

70

64 '

93*

Below 

(m

* All total gas is defined as C,-C5 except in these cases, where it is defined as C,-C4. 

111 Behar and others (1997); (21 Pepper and Corvi (1995); P1 Knauss and others (1997)
Table 8: Amounts of gas generated from kerogen above and below the deep-gas depth of 4,572 m (15,000 

refer to Ci-C5 gas, except where otherwise noted.

1 °/~'/»v»i» 1 A 

Kinetic Model Oil Type

Source-Rock Oil

Anhydrous Pyrolysis^ Oil in Source Rock*

Gas Generated

Above 4572 m

(mg/g C)

29

Below 4572 m

(mg/g C)

71

Gas Generated

Reservoir Oil

Anhydrous Pyrolysis[S1 North Sea (36° API)

Hydrous Pyrolysis1*1 Sarukawa (33.6°API)

Above 4572 m

(mg/g Oil)

2*

0

Below 4572 m

(mg/g Oil)

458*

320

Gas G

Above 4572 m 

(mg/g C)

100

Gas G

Above 4572 m 

(mg/g Oil)

370*

170

* All total gas is defined as C1-C5 except in these cases, where it is defined as C1-C4. 

141 Pepper and Dodd (1995); m Horsfield et al. (1992); (6) Tsuzuki et al. (1997)
NJ 

OO

800-

1800-

2800-

JZ

Q.3800

O>

Q

CQ

4800-

5800-

6800-

a) Type I Kerogen to Gas 

1 °C/my

Open Pyrolysis [1] 

Composite Pyrolysis [2]

I'''' I'''' I''' ' 

b) Type 

Open Pyrolysis 

- - Composite Pyro

7800-

0 10 20 30 40 50 60 70 80 90 100 6 10 20 30 40 

YieiJ (mg/g C) Yiel

Figure 1: Amount of C,-C5 gas generated from Type-I kerogen with increasing burial depth accordin

line; mBehar and others, 1997) and composite-pyrolysis (dashed line; I21Pepper and Corvi, 1995) mod

a) rC/m.y. and b)10°C/m.v. Deep-gas depths occur below the solid horizontal line drawn at 4,572 m
QOO1800-

2800-

JZ

0.3800- 

0

Q

CQ

4800-

5800-

6800-

7800- i- . i

I » 1 I I I I I I I I I I I

0

a) Type II Kerogen to Gas 

1 °C/my

 Open Pyrolysis [1]

 - - Composite Pyrolysis [2]

 Hydrous Pyrolysis [3]

i i r

i 

b) Type II K

1 0 

20 40 60 80 100 120 0 20 40 

Yield (mg/g c.) Yield 

Figure 2: Amount of gas generated from Type-II kerogen with increasing burial depth according to the 

C5 ; [11Behar and others, 1997), composite-pyrolysis (dashed line; CrC5 ; [2]Pepper and Corvi, 1995), and 

line; C,-C4 ; plKnauss and others, 1997) models at geological heating rates of a)l°C/m.y. and b)10°C/m.

below the solid horizontal line drawn at 4.572 m.
800-

1800-

2800-

Q.3800

<D

Q

15

"3 4800 

CQ

5800-

6800-

7800- . i .

I I T | I I T I I I I I I I I I I I I I

0

a) Type II-S Kerogen to Gas 

1 °C/my

 Open Pyrolysis [1]

- - Composite Pyrolysis [2]

i i i i r i i i i i

i i i i i i i i i i 

b) Type II-S 

10 

 Open Pyrolysis [1]

Composite 

Pyrolysis [2]

20 40 60 80 100 120 0 20 40 

 Yield (mg/g C) Yield 

Figure 3: Amount of C,-C5 gas generated from Type-IIS kerogen with increasing burial depth according 

line; [1]Behar and others, 1997) and composite-pyrolysis (dashed line; f21Pepper and Corvi, 1995) models 

a) l°C/m.y. and b)10°C/m.y. Deep-gas depths occur below the solid horizontal line drawn at 4,572 m.
800-

1800-

2800-

_c 

0.3800-

(D

Q

CQ

4800-

5800-

6800-

7800-

a) Type III Kerogen to Gas 

1 °C/my

 Open Pyroiysis [1]

- - Composite Pyroiysis [2]

I I I I I I I I I I I I I I I I I I I I 1 I 1 I I |T| I I IT!! I I I I I I

0 10 20 30 40 50 60 70 80

T i i I i i i i i i i i i I i i i i i I'''' I

b) Type III 

10

i i i i i i i i i i i i i i i i i i 

90 100 0 10 20 30 40 

Yiel

YieM (mg/g C)

Figure 4: Amount of C,-C5 gas generated from Type-Ill kerogen with increasing burial depth accordi

line; (UBehar and others, 1997) and composite-pyrolysis (dashed line; mPepper and Corvi, 1995) mod

a) l°C/m.y. and b)10°C/m.y. Deep-gas depths occur below the solid horizontal line drawn at 4,572 m
UJ 

NJ

800-

1800-

2800-

JZ

Q.3800H

Q)

Q

CQ

4800-

5800-

'6800-

7800-

a) Type III 1 Kerogen to Gas 

1 °C/my

Open Pyrolysis [1]

- - Composite Pyrolysis [2]

b) Type 

0 10 20 30 40 50 60 70 80 90 100 0 10 20 30 40 

Yiold (mg/g C) Yield 

Figure 5: Amount of C,-C5 gas generated from Type-Ill' (paraffinic) kerogen with increasing b

pyrolysis (solid line; niBehar and others, 1997) and composite-pyrolysis (dashed line; plPepper 

heating rates of a) l°C/m.y. and b)10°C/m.y. Deep-gas depths occur below the solid horizontal 
OJ 

OJ

800-

1800-

2800-

JC

0.3800 -US

<D

Q

m

4800-

5800-

6800-

7800-

. . . . 1 1 . 1 . 1 . 1 1 . 1 . 1 1 . 1 1 . . 1 1 1 . . 1 1 .

a) Pepper and Dodd

Sixteen Source Rock 

Samples 

1 °C/my

\

\

1

i

\ 

i

1 1 1 j * 1 1 1 1 * 1 1 1 1 1 1 1

_ _ PI

 DL

 GA

 -.PAL

 LC9

 - LC1

----- AWD

----- P4

----- P5 

 Maui

 Tu 

 - Ta

 - CO

O H t

I

-

""

--

-

-

0 50 100 150 200 250 300 350 400 450 500

Yield (mg/g C)

I 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 

b) Pepper and 

Sixteen Sour

Rock Sample

1 0 °C/my

I

l\

1\m.

^m

\

0 50 100 150 200 

Yield 

Figure 6: Amount of C,-C5 315 generated from th^ cracking of oil in 16 different source rocks v/ith in

to the anhydrous-pyrolysis model (solid lines; Pepper and Corvi, 1995) at geological heating rates of 

Deep-gas depths occur below the solid horizontal line drawn at 4,572 m. Abbreviations for source ro

SM = St. Medard, GA - Garlin, KCF = not given, PAL == not given; LC9 = LC995, LC1 - LC1005, 

Pematang 45.2, PS = Pematang 52.7, Maui = Maui, Tu = Tuna, Ta = Tarakan, CO = COST, Ha = H

Westfield. The bold-solid St. Medard (SM) curve was selected to be the single representative gas-gen
800-

1800-

2800-

Q.3800-

0)

Q

CD

4800-

5800-

6800-

a) Oil to Gas 

1 °C/my

 Closed Anhydrous Pyrolysis [4]

- - - Hydrous Pyrolysis [5]

b) O

10 

Close

- - - Hydro

7800-

0 50 100 150 200 250 300 350 400 450 500 0 50 100 150 200 

Yield (mg/o nj|) Yield 

Figure 7: Amount of gas generated from the cracking of reservoir oil with increasing burial depth accord

pyrolysis (solid line; Ct-C4 ; [4]Horsfield and others, 1992) and hydrous-pyrolysis (dash-dot line; C,-C4 ; [5]

models at geological heating rates of a) l°C/m.y. and b)10°C/m.y. Deep-gas depths occur below the soli

4,572 m.