Oil and Gas Evolution Kinetics for Oil Shale and Petroleum Source Rocks Determined from Pyrolysis-TQMS Data at Multiple Heating Rates

Transcription

1 UCRLJC088 PREPRINT Oil and Gas Evolution Kinetics for Oil Shale and Petroleum Source Rocks Determined from PyrolysisTQMS Data at Multiple Heating Rates Robert L. Braun Alan K. Burnham John G. Reynolds This paper was prepared for submittal to Energy & Fuels November 99 This is a preprint of a paper intended for publication in a journal or proceedings. Since changes may be made before publication, this preprint is made available with the understanding that it will not be cited or reproduced without the permission of the author.

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3 Oil and Gas Evolution Kinetics for Oil Shale and Petroleum Source Rocks Determined from PyrolysisTQMS Data at Multiple Heating Rates Robert L. Braun, Alan K. Burnham, and John G. Reynolds Lawrence Livermore National Laboratory, University of California Livermore, California 90 Abstract Seven oil shales and petroleum source rocks were subjected to programmedtemperature pyrolysis at heating rates of and 0 C/min using triplequadrupole mass spectrometry to monitor volatile compound evolution. Kinetic parameters were determined for evolution of hydrocarbons and various heteroatom species. Normalized cumulative generation of oil, light hydrocarbon gas (CC), methane, carbon dioxide, acetic acid, hydrogen sulfide, and methylthiophene were calculated for generic geologic conditions using kinetic parameters that were lumped and averaged into type I, Ha, and lib source rock classes. The four heteroatom species are largely generated before oil and the hydrocarbon gases. Using these kinetics to simulate hydrous pyrolysis gives favorable comparison with hydrous pyrolysis measurement of acetic acid generation for several different source rocks. Introduction A variety of techniques have been used to measure oil and gas generation kinetics for kerogen pyrolysis, but most workers do not report detailed information for individual pyrolysis products. The latter information is important for many reasons: to help establish the origin of activation energy distributions, to provide diagnostics of kerogen structure and depositional conditions, to understand variations of gas/oil ratios during kerogen maturation, to make complex chemical models needed for realistic calculation of overpressuring, and to define the source terms for components that are involved in important secondary reactions, such as mineral diagenesis. Laboratory pyrolysis at a constant heating rate using triplequadrupole mass spectrometry (TQMS) as the detection method is particularly wellsuited for measuring the generation rate of individual pyrolysis products. It provides online, timeresolved analysis to follow the evolution of various light hydrocarbons and N, S, and Ocontaining

4 compounds as a function of temperature. Pyrolysis at a single heating rate allows determination of evolution range and Tmax for that heating rate. Reynolds et al} applied this method at 0 C/min to study oil shale and petroleum source rocks. Multiple heating rates, however, are required to determine more useful kinetic parameters. This reports adds C/min data for of the sampes previously presented, allowing the determination of generation kinetics for many individual pyrolysis products. These kinetics are useful in developing generic chemistry models for type I and type II source rocks. Experimental Section The instrumentation, samples, and pyrolysis experiments are described by Reynolds et al} PyrolysisTQMS data were collected at and 0 C/min for one lacustrine oil shale (AP), two highcarbonate marine source rocks (LLNA and WNZN), and four lowcarbonate marine source rocks (NAKY, KIMR, WDFD, and PHOS). We will later refer to these three groupings as types I, Ha, and lib. Table gives several important properties of the materials. Pyromat data show that hydrocarbon generation for type I is mosdy at one activation energy, while for type Ha and lib it spans a significant range of energies. Although calibrated thermocouples were used at both heating rates, preliminary data analysis indicated that the temperatures for the C/min experiments were still significantly in error for most of the samples. Therefore, a temperature correction was applied to the C/min data to make the mean calculated activation energy for CH8 and m/z (primarily the CHp~ ion) agree with our Pyromat results. These two species were chosen because they had strong TQMS signals and they should have generation rates similar to the hydrocarbons measured by the Pyromat. The indicated temperature corrections ranged from 0.9 C for AP to. C for PHOS. Therefore, the kinetics presented in this report can be considered as calibrated to kinetics determined in more accurate experiments. Results and Discussion Analysis of TQMS data. We selected species (or combinations of species) for kinetic analysis. Species designations are shown as the first column of Table. The meanings of most are selfevident. The exceptions may be TLO (total light organics that pass the 0 C trap), CC (combination of 0*, CH<, CH8, and C HK)) and Ci~ C (combination of CH and CC). For CO and HS, effort was made to use only the lowertemperature portion of the rate profiles (~00 C) from kerogen pyrolysis and to

5 exclude the portion from mineral decomposition. The same set of species was analyzed for all seven source rocks, except satisfactory CO data were not available for KIMR. For each species or combination, temperaturecorrected data were smoothed by means of a running point average for time, temperature, and rate. The reader is referred to Reynolds et al. to see the kinds of evolution profiles analyzed. The kinetic analysis was done in several ways with our KINETICS program. Detailed results of the kinetic analysis are given in the Supplementary Material. First, Tmax at each heating rate was determined by a parabolic, leastsquares fit of the top 0% of the reaction rate profile. Using a larger portion of the profile is usually undesirable, because it is more likely to depart from a stricuy parabolic shape. For some of the profiles, however, it was necessary to use the top % of the profile, since the top 0% was too noisy to give a reliable determination of Tmax This was true for CHCOOH with all samples and for a few other species with some of the samples. The T^x results are shown in Table. These are useful in indicating the relative order of evolution of the pyolysis products. They are also useful in the kinetic analysis described next. Our KINETICS program performs a number of simple kinetic analyses as part of the initial data reduction. Often the most useful one is the approximate Gaussian analysis, when data are available at or more heating rates: () initial values of A and E 0 are determined by linear regression from the shift of T^^ with heating rate; () an approximate Gaussian distribution parameter (CTE) is estimated from a correlation function of the width of the reaction profiles; () a correction term for Tm^ is estimated from another correlation function of A, E 0, and <?&; and () final values of A and E 0 are again calculated from the shift of the corrected T ma, x with heating rate. Useful kinetic parameters can be derived by this method, if a wide range of heating rates is used (preferably a factor of 0) and if the temperatures are measured to an absolute accuracy of a few C with no systematic dependence of the temperature error on heating rate. For the factor of 0 in heating rates used here, a temperature error of only C at one heating rate and + C at the other heating rate would cause an error of about kcal/mol in the principal activation energy and a compensating error of about a factor of in the frequency factor. Effects of temperature measurement errors on the quality of derived kinetic parameters are discussed by Burnham et al. and by Braun and Burnham. In this work, we tried to minimize the temperature error by the calibration procedure described in the experimental section. The other principal error in Tmax is due to the inability of exactly determining the point at which the maximum rate is reached. Errors far greater than C can easily arise for species having a noisy TQMS signal. Therefore, the quality of the approximate Gaussian parameters determined from

6 TQMS data is not particularly good for many species and direct use of the parameters for geologic extrapolation is not recommended. For most samples, the approximate Gaussian analysis could not be done for H or CO, because the data were inadequate to define the width of the evolution profiles. The next step of our analysis consisted of using the approximate Gaussian parameters as a starting point for a more rigorous, nonlinear regression analysis to more accurately determine A and a discrete E distribution. The results of this analysis suffer from the same temperature uncertainties that affect the Tmaxshift results, with large, inconsistent variations in A. For comparison purposes, we condense the entire E distribution into a single energy a ve> the average energy weighted by the distribution fractions. This is a better method of estimating the principal activation energy than just picking the energy having the maximum fraction in the distribution, particularly for distributions having several large fractions of similar magnitude. We find large variations in A and E iwt among the species for a given sample. We suspect that these are statistical variations caused by the broad minimum in regression space due to noise in the TQMS signal. Ungerer illustrated that various measurements of pyrolysis kinetics show a high correlation between A and the principal E, corresponding to AE couples yielding approximately the same rate constant at a given temperature characteristic of laboratory pyrolysis measurements. A wider range of heating rates than the factor of 0 used here would increase the timetemperature resolution in helping to select the correct AE couple. Even then, however, the weak TQMS signal for some of the species may preclude satisfactory results. Therefore, we explored the following alternative. A rigorous, discrete analysis using an A fixed at the value measured for Pyromat data gives an E distribution for CH8 and m/z with a principal energy which closely matches that deduced from Pyromat data. Using the same fixed A for all TQMS species, moreover, eliminated most of the random fluctuations in the average E among the species. In this analysis we used fixed A values of x 0, x 0, and x 0 s" for types I, Ha, and lib, respectively. These are actually a factor of smaller than the Pyromat averages for type I, Ila, and lib samples. The reason for the factor of is that we believe a shift of about kcal/mol in E from that given by the discrete analysis of Pyromat data is best for geologic extrapolation. Using a fixed A for all pyrolysis products of a given material requires that the progression of the reaction be the same at laboratory and geologic conditions. Although this assumption is not necessarily the case, it is justified by the large statistical variations in A obtained with our data. Again, for comparison purposed, we condense the entire E distribution into a weighted average E[y &.

7 Table gives the three E parameters (E 0, a ve» and a ' ve ) averaged over all four of the type lib samples. Both E 0 (from the approximate Gaussian analysis) and E av e (from the rigorous discrete analysis) show large variations among the species and have relatively high standard deviations for a given species. For E^ (from the discrete analysis with fixed/!), however, the differences among the species are much smaller and are consistent with generation of the heteroatom species at a lower activation energy and generation of H and CH at a higher activation energy than the bulk of the hydrocarbon products. Furthermore, the standard deviations are very small for E ve. This gives us some confidence in the validity of the fixeda analysis. Comparing the weightedaverage E's is not strictly valid in analyzing reaction rate profiles that arc truncated at the higher temperatures, since it will underestimate the weighted average of the complete E distribution. Only H, CO, and sometimes HS had truncated reaction rate profiles. The rate profile for H was truncated because Hj evolution continues from pyrolysis of residual organic matter to temperatures far higher than we used. E ve is probably least meaningful for H, because the principal peak of the rate profile and only part of the residual pyrolysis were included in the analysis. The rate profiles for organic CO and HS were truncated to eliminate interference from inorganic CO and HS. Despite this, E a ' ve for these species are probably quite meaningful, because most of the energies associated with release of the organic portions are included. Detailed kinetics for hydrocarbon and heteroatom generation. The fixed A's and complete E distributions determined in the preceding analysis could, in principle, be used to model pyrolysis reactions in great detail. In practice, however, using such a large number of individual sets of rate parameters is probably unnecessary and may require excessive computer time. Therefore, we have simplified the kinetics for hydrocarbon generation. For light hydrocarbon gas we normally use the separate results for CH and CC from our discrete analysis with fixed A. Alternatively, it may be adequate in some models to use the single combined species CC for the light hydrocarbon gas. The average kinetic parameters for type I, Ha, and lib samples for these three species or combinations are given in Table. The oil generation parameters were determined by subtracting the TQMS hydrocarbon gas contribution from the total hydrocarbons measured by Pyromat. These kinetic parameters, or a subset of them, will be adequate for modeling hydrocarbon generation in many basin analysis models (e.g., model of Braun and Burnham). 6 In a very detailed chemical model, however, it may be desirable to account for the significantly different kinetics for the generation of heteroatom species (such as CO, CHCOOH, HS, and CHCHS). The average kinetic parameters for type I, Ha, and

8 lib classes for these four species are given in Table and the kinetic parameters for all seven individual source rocks are given in the Supplementary Material. We emphasize that only one type I sample (AP) was included in our analysis. For most species, the TQMS data for AP were representative of other type I samples not analyzed in detail. This is not true for CHCOOH, which evolved at significantly lower temperatures for AP, as illustrated by published rate profiles. Other type I profiles for CHCOOH, in fact, appear to be more similar to those of type Ha and lib samples. Comparisons of calculated rate profiles for four species at 0 C/min using the type lib Edistribution and fixed.a from Table are shown in Figure along with the measured rate profiles for the type lib samples. The best agreement among the measured profiles and with the calculated profile was obtained for m/z and a few other hydrocarbon species that had a strong TQMS signal. Most species had agreement as good as that shown for CC and CHCHS. The poorest agreement was obtained for CHCOOH. Comparisons of calculated and measured acetic acid generation are shown in Figure. The measurements are from h, hydrous pyrolysis experiments of Lundegard and Senftle using a nonmarine shale and Barth et a/. 8 using a marine shale. The two sets of measurements are essentially identical. Although it is not certain that CHCOOH generation in hydrous pyrolysis is governed by the same mechanism as in our opensystem experiments, the final half of the measured generation agrees very well with that calculated with our type Ha and lib kinetics. The single E of. kcal/mol reported by Barth etal., however, is markedly lower than our weighted average of 9 and 0 kcal/mol for type Ha and lib, respectively. A likely explanation is that large errors in E can be obtained by interpreting rate data in terms of a single E, when a distribution is actually required. Burnham and Braun 9 have previously discussed this problem in interpreting oil generation data from hydrous pyrolysis. Using the kinetic parameters in Tables and, we calculated the generation of oil, CC, CH, C0, CHCOOH, H S, and CHCHS at a typical geologic heating rate of C/My. Comparisons of normalized cumulative generation are shown in Figure for AP, Ha, and lib. Generation of the four heteroatom species largely precedes oil generation, while generation of much of the hydrocarbon gas (especially CH) follows oil generation. There is some departure from these generalizations, because the kinetics for oil were determined from Pyromat data. Pyromat data appear to give a smaller E distribution compared with TQMS data, due to the inherently greater dispersion in the TQMS measurements. For example, the Gaussian distribution parameter, CT E, determined 6

9 by Pyromat data for oil is approximately % of E 0 smaller than the value determined by TQMS data for TLO. Eglinton et a/. 0 demonstrated that thiophenic sulfur is eliminated from kerogen at an earlier stage of maturation than hydrocarbons. The kinetic parameters from this report provide a means to compare the laboratory and the natural maturation trends. Figure shows our calculated ratio of CHCHS precursor to TLO precursor at a heating rate of C/My as a function of RockEval r^x, starting with equal amounts of each precursor. The calculated trends for type II kerogen follow those reported by Eglinton et al. Our E distribution to describe HS generation profiles from type I and II source rocks agrees qualitatively with the HS kinetics of Kelemen et al. for coals. However, their more accurate data indicated a lower A and a compensatingly lower mean E for HS compared with hydrocarbons. We can not eliminate that possibility for type I and II source rocks. Kelemen et al. were also able to use XANES spectroscopy to demonstrate that the E distribution is due in part to faster generation of HS from aliphatic sulfur in the coal than from aromatic sulfur, and we suspect the same may be true for type I and II source rocks. Summary and Conclusions Activation energy distributions are required to describe the evolution of individual gas species from kerogen. Although our data are not sufficiently accurate to determine absolute kinetic parameters, the data are consistent with a mean E in the 0 kcal/mole range for all species investigated. This implies that relative evolution rates of the gas species will be similar in natural and laboratory maturation as long as the mechanism is sufficiently similar. For example, the kinetic measurements are consistent with early elimination of oxygen and sulfur from the kerogen. Because the amount of kinetic information obtained from these experiments can be overwhelming, the results from individual samples have been averaged to obtain approximate values for type I, Ha, and lib source rocks. These kinetic parameters have been useful for making generic kinetic models of kerogen maturation for basin modeling purposes. 6 Acknowledgements This work was performed under the auspices of the U.S. Department of Energy by the Lawrence Livermore National Laboratory under Contract W0ENG8. It was supported by the US DOE Offices of Basic Energy Sciences and Fossil Energy and a group of industrial sponsors.

10 References. Reynolds, J. G.; Crawford, R. W.; Bumham, A. K. Energy Fuels 99,, 0.. Braun, R. L.; Bumham, A. K.; Reynolds, J. G.; Clarkson, J. E. Energy Fuels 99,, 90.. Braun, R. L.; Bumham, A. K. Lawrence Livermore Nat. Lab. Report UCID88, Rev., 990, Livermore, CA, Avail. NTIS, Springfield, VA.. Bumham, A. K.; Braun, R. L.; Gregg, H. R.; Samoun, A. M. Energy Fuels 98,, 8.. Ungerer, P. Org. Geochem. 990,6,. 6. Braun, R. L.; Bumham, A. K. Lawrence Livermore Nat. Lab. Report UCRLJC 0, 99, presented at th Int. Meeting on Org. Geochem., Manchester, Sept. 60, 99.. Lundegard, P. D.; Senftle, J. T. Appl. Geochem. 98,, Barth, T.; Borgund, A. E.; Hopland, A. L. Org. Geochem. 989,, Bumham, A. K.; Braun, R. L. Org. Geochem. 990, 6, Eglinton, T. I.; Damste, J. S. S.; Kohnen, M. E. L.; de Leeuw, J. W.; Larter, S. R.; Patience, R. L. In Geochemistry of Sulfur in Fossil Fuels; Orr, W. L.; White, C. M., Eds.; ACS Symposium Series 9; American Chemical Society: Washington, DC, 990; pp 96.. Kelemen, S. R.; Gorbaty, M. L.; Vaughn, S. N.; George, G. Prepr. Pap.Am. Chem. Soc, Div. Fuel Chem. 99, 6(),. 8

11 Table. Selected properties of source rocks. Other properties are given by Reynolds et al. Type ///* (mg/g TOC) T b "max CO E c (kcal/mol) pd (%) AP LLNA WNZN NAKY KIMR WDFD PHOS I Ha Ha lib lib lib lib All * Hydrogen Index from RockEval data. b Tmax at C/min from Pyromat data. c Principal discrete activation energy from Pyromat data. d Portion of hydrocarbons generated at the principal activation energy. Table. Experimental ma x ( C C) at heating rates of and 0 C/min determined by parabolic, leastsquares fit of top 0% of generation profile, unless otherwise indicated. C H 8 m/z TLO b H CH C C CC C H AP C H Q H 6 CHCHS 0* CH COOH0* H S 9 co * 6* 0 LLNA * * WNZN * * 08 NAKY 0* * 90* 6* 90 6 * * 8* 8* 9 9 * These used top % of generation profile for determining T, b TLO total light organics which pass the 0 C trap. KIMR * * * 8 9 * 8 WDFD * 8 8* 80* * 86* * PHOS * 0 8 0* * * 9 0 * 6* 6 9

12 Table. Activation energies averaged over the four type lib source rocks. E 0 * (std.dev.) (kcal/mol) Eave b (std.dev.) (kcal/mol) E^ec (std.dev.) (kcal/mol) C H 8 m/z TLO H CH C C QC C H 0 C H C 6 H 6 CHCHS CHCOOH H S e COf d d (.9) () (.) (0.6) (.) (.) (.9) (.6) (.6) (6.) (.0) (D (.) (.) (.) (.0) (6.) (.) (.9) (.) (.) (.0) (.) (8.) (.0) (.) (0.) (0.) (0.) (0.) (.) (0.) (0.) (0.) (0.) (0.) (0.) (.9) (.) (0.9) a 0 = central E of approximate Gaussian analysis without fixed A. b ave = weightedaverage E of discrete distribution analysis without fixed A. c a ' ve = weightedaverage E of discrete distribution analysis with fixed A = xl0 s". d Insufficient data. e Data truncated to eliminate interferences from inorganic sources. 0

13 Table. Pyrolysis model for type I, Ila, and lib source rocks, with hydrocarbon potentials [HI (mg/g TOC)] and kinetics [A (s _ ), E (kcal/mol), and ^distribution (%)]. I Ha lib OU CH C C C r C OU CH C C C r C Oil CH C C C r C HI A xl0 xl0 xl0 E Distribution Distribution Distribution F' 8 6

14 Table. E distributions (kcal/mol and %) from discrete Edistribution analysis for the principal heteroatom species generated from kerogen pyrolysis with A = xl0, xl0, and xl0 s _, for AP and type Ila and lib source rocks, respectively. C0 CH COOH a H S CHCHS AP Ila lib AP Ila lib AP Ila lib AP Ila lib E Distribution Distribution Distribution Distribution E' CHCOOH for AP is not representative of other type I samples.

15 .0 m/z I T "i r NAKY KIMR WDFD PHOS I c c I I I * ft* r * Jm t V A* \ * * «A # V "A _.K,wi'j ) & ^ s 0.0 CHCOOH 0.6 " * * /' * \ /»\ «. > t&u ^ ^ r? Temperature, C Figure. Measured generation rates at 0 C/min (symbols) compared with calculated rates (lines) using kinetic parameters in Table for type lib source rocks.

16 Temperature, C Figure. Measured cumulative generation of acetic acid from h hydrous pyrolysis experiments (symbols) compared with the calculated generation (lines) using kinetic parameters in Table for AP and type Ha and lib source rocks. Acetic acid generation for AP is not representative of other type I samples.

17 .0 AP 0IL \ f "L^Z^^^ 0.6 CHC00H ^s^ I \. ^ ^ CHCHS ^ / p >^ /^c c«/ y^ / ' / / I J ' V si s*s ^CH 0.0 Ha i ' fyij 0.6 CHCHS OIL^ c c, E u o H S^ (J ' / '/ / // / o Z ' ^r* **^^~** 0 * ^.0 lib 0,L \ ^ _ y^ CH CHS^ /f // CH COOH^. / /if/ \ / / ' / c \ y ^v / ' / ^^ / ' / ^/ / / '/ >/ / y / CC ^CH Temperature, C Figure. Calculated cumulative generation of seven species at C/My using kinetic parameters in Tables and for AP and type Ha and lib source rocks.

18 ..0 m> i Ua \ AP i i \ \ \ % 0.6 oc V ^ ^> RockEval Tmax, C ure. Calculated normalized ratio of methylthiophene precursor to total light hydrocarbon precursor as a function of maturation at C/My using kinetic parameters in Table for AP and type Ila and lib source rocks. 6

19 Supplementary Material Table Al. Measured T max and calculated kinetics parameters using several models. AP ^ H 8 m/z TLO H CH CC qc QHjo ^^0 C 6 H6 «CH C H S *CH COOH H S C0 LLNA C H g m/z TLO H CH C C CC C H]o QHJQ C 6 H 6 CH C H S CH COOH H S C0 WNZN C H g m/z TLO H CH C C C " C ^ H 0 CH0 C 6 H 6 CH C H S «CH COOH H S C0 NAKY «C H m/z TLO H CH Measured Tmax Approximate Gaussian Discrete l C/min 0 C/min A E 0 as A ave ^ave ( C) ( C) (s ) (kcal/mol) (% of E ) (s ) (kcal/mol) (kcal/mol) E+.6E+.E+.0E+ 6.9E+.6E+ 8.E+.0E+.6E+.E+.E+.E+.E+.E+.E+.8E+ 9.E+0.0E+.E+.E+.6E+.E+ 8.E+.9E+.E+.6E+.E+.E+.E+.E+.E+.0E+.E+.8E+.E+ 8.E+.8E+.E+0.9E+.E+.0E+ 9.E+ 6.E E+.E+.8E+.E+ 9.E+6.E+.E+.8E+.E+.E+.E+.0E+.E+6.E+.8E+.E+.E+.E+0.6E+.E+ 8.E+0 8.6E+.0E+.E+ 8.E+.E+.0E+.E+.E+.E+.E+.E+.E+.E+.8E+.E+ 8.E+ 9.9E+0.8E+.8E+0.8E+.E+.E+.E+.E+.E+.E f ' A=.E+ a A=.E+ a A=.E+ a A=.E+ a

20 CC c c CHJO ^^0 CeHg «CH C H S *CH COOH H S C E+.0E+.E+.E+ 8.E+.E+.E+8.9E E+.E+.6E+.E+.6E+.E+.6E+6 8.e+ 6.9E t KIMR ^^8 m/z TLO H CH CC 0 ^ CH0 'C H 0 C 6 H6 CH C H S *CH COOH H S C E+.E+.6E+.E+.E+.6E+.E+08.6E+.E+.E+09.6E+09.9E Satisfactory data not available E+ 9.6E+.E+8.E+.E+.E+.6E+.E+0 8.E+0 6.6E+.0E+0.0E+0.8e t9. A=.E+ a WDFD C H 8 m/z TLO H CH CC CjC Q^io C H 0 'CeHs CH CH S «CH COOH *H S C E+.E+.9E+.0E+ 8.E+ 6.0E+6.0E+.E+.E+.E+.E+.E E+.E+.8E+.E+ 9.E+6.E+0.0E+6.E+ 6.E+.E+ 8.9E+.E+.9E+ 6.E A=.E+ a PHOS Q} H 8 m/z TLO H CH CC C^C^ CH0 *C H 0 C 6 H6 CH CHS «CH COOH *H S C E+8.E+ 9.6E+9.0E+.E+ 6.8E+6.8E+.E+.E+.E+.0E+.E+.9E E+6.E+.6E+0.6E+.E+.E+.E+6.E+ 6.9E+.9E+.E+.0E+.E+.6E A=.E+ a a Fixed A value from Pyromat measurements. These used top % of generation profile for determining T ma x'. others used top 0%. Data truncated to eliminate interferences from inorganic sources. 8

21 Table A. Kinetics for generation of four heteratomic species from kerogen: [A (s ), E (kcal/mol), and Edistribution (%)]. A = E F' E F' ^ave " E F' *ave E F' c ave AP.E = = = :. LLNA.E WNZN.E+ NAKY.E+ KIMR.E+ WDFD.E+ Edistribution for generation of C Edistribution for generation of CHCOOH E<listribution for generation of H S PHOS.E Edistribution for generation of CHCHS