Evaluation criteria for gas source rocks of marine carbonate in China

PROGRESS IN NATURAL SCIENCEVol. 15, No 9, September 2005Evaluation criteria for gas source rocks ofmarine carbonate in ChinaWANG Zhaoyun**, ZHAO Wenzhi and WANG Yunpeng(1. Research Institute of Petroleum Exploration Development, PetroChina, Beijing 100083, China; 2. Guangzhou Institute of Geohemistry, Chinese Academy of Sciences, Guangzhou 510640, China)Received December 19, 2004; revised January 24, 2005Abstract Hydrocarbon generating and expulsion simulation experiments are carried out using samples artifically matched betweenthe acid-dissolved residue of relatively low-maturity limestone and the original sample. This work makes up for the insufficiency of sourceock samples with high abundance of organic matters and low maturity in China. The organic carbon content of the 10 prepared samplesvaries between 0. 15% and 0. 74%. Pyrolysis data and simulation experiment results of hydrocarbon generating and expulsion, whichwere obtained by a high-temperature and high-pressure open system, indicate that the lower limit of organic carbon content for marine carbonate rock to generate and expel hydrocarbons is 0.23%-0 31%. In combination with the numerical analysis of organic carbon in marine carbonate rocks from Tarim Basin, Sichuan Basin, Ordos Basin and North China, as well as the contribution of these gas source rocksto the discovered gas pools, we think that the organic carbon criterion for carbonate gas source rocks should be 0. 3%Keywords: carbonate gas source rock, gas-generating efficiency, evaluation criteria, simulation experimentPrevious researches have shown that the originalMarine gas source rocks in China can be classisedimentary environment, late superimposition, and fied into two types, that is, clastic rock and carbontransformation of basins of the marine sequences in ate rock. The evaluation criteria for marine clasticChina are different from the typical marine sedimen- rocks are the same as for non-marine mudstone, andtary basins in other parts of the world 4. In Chi- this practice has been generally accepted by the China, a number of large-size oil/ gas fields have been nese researchers and explorationists. There are manydiscovered in the marine strata of Tarim, Sichuan and examples demonstrating that high-abundance marineOrdos Basin 5-8, making marine strata an important carbonate rocks could, as effective source rocks, formsuperseding area for hydrocarbons. Therefore, itoil/gas pools with great commercial value. Table 1very important to probe into petroleum geology, hylists the organic carbon content of some marine gasdrocarbon resource potential, and distribution of masource rocks in the worldrine strata in ChinaTable 1. Organic carbolBasinOil/gas fieldGas source rocksTOC(%)ReservoirEast siberYurubchenskoyL, mudstone, marl2.4-8.7Caspian Sea CoastalmichiganO, shale limestorOnian-ScypionO, shale limestone0.5-1.5Cabin creekD3 shale& marla) Total organic carbon: b) in depression: c) maxium 4.23Concerning about whether the low-abundand中国煤化 Isis of large gas fields in(ToC<0.5%) marine carbonate rocks in Chinaexample. Huang etcould act as effective source rocks to form oil/HCNMHhat the genesis shouldpools with commercial value, many researches have be of a combined type: both the Lower-Paleozoic mabeen conducted but no final conclusion has been rine carbonate and the Upper- Paleozoic continental四2数State Basic Research Development Program of China(Grant No, 2001CB209100)denceshouldbeaddressedE-mail:wzy@petrochina.com.cnProgressinNaturalScienceVol.15No.92005www.tandf.co.uk/journals811marine alternating coal strata make contributions, lation experiment. To solve this problem, two ap-with the contribution proportion at about 50% and proaches have been adopted: the first is to select sam85%90%, respectively. In accordance with Dai et ples with low maturity and high organic abundancealL12, 13,the Upper-Paleozoic coal measure strata are from other countries for the study, e.g. Jordan limethe main contributor, while Xia[ 14 believed that it is stone 15, 16; the second is to use prepared kerogen tomainly contributed by the Upper- Paleozoic coal mea- conduct simulation experiment under various condisure strata, and, even if marine gas source rocks tions[]. However, geological background of thesemake some contributions, it is contributed by the samples is not the same as the Chinese samples, andlimestone developed in the Upper- Paleozoic continen- the geological conditions represented by kerogen datatal and marine alternating strata. Obviously, they are far from the actual ones. Therefore, we have tohave no consistent opinions on such a question. To prepare a series of samples with distinct abundance ofddress this question, we selected acid-dissolved organic matter, avoiding the effects of sedimentaryresidue of limestone with relatively low maturity and environment and different evolutional degree onartificially matched it with original samples to prepare perimental data, and making the hydrocarbon genesamples containing different organic carbon contents. ating environment of organic matter catalytic actionUsing these prepared samples, we analyzed rock-eval of clay minerals and trace elements on gas generatingand established the lower limit value for significant closer to the actual geological conditionsgas generating through hydrocarbon generating andexpulsion simulation experiments. In combinationAmong the Lower- Paleozoic and earlier strata inwith the numerical analysis of organic carbon in gas China, the profile of Majiagou Group, located atsource rocks from the Chinese marine-genesis gas Zhaogezhuang, Tangshan in North China, is featuredpools, a reasonable evaluation criterion valuable for by its low evolutional degree, complete basic fieldexplorations of marine carbonate gas source rocks was work, and abundant experimental research dataset up.Therefore, samples from this group were selected forthis study. After analyzing the basic geochemical data1 Lower limit of organic carbon determined of 27 Cambrian and Ordovician samples, we selectedby the gas-generating simulation experiment of the micritic micaceous limestone of Maer Section ockcarbonate rocOrdovician System as the original samples(Table 2)The original sample has a low abundance of organic1. 1 Selection of original samplesmatter(0. 13 %)and with Tmax at 435C, apparentvitrinite reflectance at 0. 7%( calculated on the basisThe present high-evolution degree of the Chinese of asphalt reflectance ) hydrogen index at 231carbonate rocks makes themselves very difficult to g I. ToC, organic matperform hydrocarbon generating and expulsion simu- bonate content at 80.6g er being Type ll, and car-Table 2. Original sample and acid-dissolved residue for the simulation experimentSample( code) TOc(%) Tmx(C) VR a (%) S,(mg.g )S,mg.g )IH(mg.g Type Carbonate content(%)Original (y)0.70.020.30II80.6Residue(s)3,43a)VR. is marine vitrinite reflectance1. 2 Sample preparationthe acid-dissolved residue were put together to produce 10 samples of organic carbon ( Table 3). PyrolyThsample was crushed to 60 mesh, sis analysis was carried out for each sample, and 4then 800 g of the power was mixed with 6 molL sanHCI solution, and stirred thoroughly. The residue or中国煤化工 ritical condition( basedted for gas generatingwas washed by distilled water three times and dried in andCNMHGeriments in a pressureair. After this treatment, the organic matter was relopen system, by which their organic carbon contentatively enriched, and the organic carbon content inwas determined to be 0. 17%,0.23%,0.31% andcreased from 0. 13% to 1.42 %(Table 2)Atd在数捍 proportions, the original sample andThe gas generating and expulsion simulation exwww.tandf.co.uk/journalsProgressinNaturalScienceVol.15No.92005periment was conducted under the pressure of 20 MPa each temperature point, 80 g prepared sample waswhich was created by a hydropress machine. The heated to the desired temperature at a rate of 50 Csimulation temperature was from 250C to 600C h, then staying for 48h, and the resulting gas andwith 8 points in total, and at an interval of 50C. At liquid were collected quantitativelyTable 3. Samples of organic carbon preparedSample code 27y: 1s 22y: 1s 16y: Is 13y: 1s 10y: Is 7y: Is 5y: 1s 3y: 1s 2y: Is ly: IsOrganic carbon(%)0.150.170.200.2000.280.310.511. 3 Experimental results and discussion1.3.2 Gas generating and expulsion experimentperformed in the pressure open system In accor1.3.1 Analysis of pyrolysis data The results of dance with the increase relations between pyrolysedcontent of the 10 samples, pyrolysed hydrocarbon hydrocarbons and organic carbon, we selected 4 sampyrolysis data analysis, thd the relationship be-ples for conducting the gas generating and expulsiontween effective carbon index and organic carbon con- experiment in a high-temperature and high-pressuretent are shown in Fig. 1. From Fig. 1, it can be seenthat the organic carbon content of 0. 23% is a crucial ples are 0. 51%,0.31%,0.23% and 0.17%,revalue. For samples with the cospectively. Fig. 2 shows the by-stage and cumulativethis value, their increase rates of pyrolysed hydrocarbons and effective carbon along with the increase of gas expulsion volumes of eac sampleorganic carbon are different. The comparison of theThe by-stage gas expulsion volume of the 8fitted curves between Zone I and II shows that when perature points from 250 C to 600 C shows the gas-TOC0. 23%, though contents of pyrolysed hydro- generating volumes contributed by different organiccarbons and organic carbons are elevated along with matter in carbonate rocks at different evolutionalthe increase of the content of organic matter, the stages. According to variations of gas expulsion volvariation is insignificant: when TOC is higher than umes, the entire process of gas generating and expul0. 23%, pyrolysed hydrocarbons and organic carbons sion could be classified into 3 phasesincrease substantially along with the increase of thecontent of organic matter. Therefore, 0. 23% is thePhase I: The temperature is below 250Clower limit for marine carbonate rocks to extensively I in Fig. 2). During phase I, gas generating and expulsion volume is primarily contributed by soluble organic matter in source rocks2.0Phase II: The temperature range is 250-400 Cbp1.2II is extremely small gas generating and expulsionvolumes. Either the low- or high-abundance gassource rocks have limited or zero expulsion volumeindicating kerogen has not been extensively crackedfor generating gas in this phaseTOC (%020Phase III: The temperature is above 400 CZone iii in Fig. 2). In this phase, thesion volume increases largely because of the extensivegas generating by cracked kerogen. However, the increanif灬r灬 t for samples with diffeYH史中国煤化工. For the two samplesCNMHGf0.51% and 0.31%respectivelby-stage increase rate of expulsionTOC (%)volume is higher, especially at high temperature(550C); while for the other two samples with orFig, I. Vaof pyrolysed hydrocarbons and effearbonganic carbon content of 0. 23 and 0.17% respedong with万方数报 of organic carbonProgressinNaturalScienceVol.15No.92005www.tandf.co.uk/journals813By-stage gas production(m.t)In addition, a checking and collection device for100liquid hydrocarbons was used in the experiment. For△TOC=0.51%the samples with organic carbon content of 0. 51%TOC=0.31%0. 31%,0.23% and 0. 17%, the cumulative oil gen300+TOC=0.23%一TOC=0.17%erating volumes sample weight is 80 g) are 12.5ll7.8, 6.8 and 0. 1 mg, respectively. Besides the rela-tion with Type II organic matter of source rock, theextremely small oil generating volume is primarily dueto that, under the high-temperature condition, thehigh-energy rate for kerogen to convert directly integas is predominant. The converting rate is several orders higher than that of the low energy in the initialconversion process from kerogen to oil17.Therefore, the direct degradation and gas generating byCumulative gas production(mr")kerogen mainly occurred at high temperature duringexperiments△TOC=0.51%1.3.3 Theoretical basis for the qualitative change ofo TOC =0.31+TOC=0.23%gas expulsion volume under the critical conditionTOC=0.17%The essential condition for gas source rocks to expgas is that the gas generating volume should exceed。△tion or dissolution by rocks or organic matter, gas diffusion, etc. When the organic carbon content is lowthe gas generating volume is small, and the generatedgas volume will not exceed the loss volume (i.e. nogas expulsion occurs). Along with the increase of organic matter and when the generated gas volume exFig. 2. Comparison of by-stage (a) and cumulative (b) gas exceeds the gas loss quantity, gas expulsion occurssion volumes of carbonate samples above and below the criticalWith the increase of the organic carbon content, theconditionaccumulated organic matter extensively transforms into effective gas expulsion volume, eventually leadingsamples, their cumulative gas expulsionalmost the same, indicating that, whento the qualitative change of gas expulsion volumethe organic carbon content is below 0. 31%,the totalThe research on maximal adsorption power ofgas generating volume will not increase substantially different source rocks indicates that (1) comparedalong with the increase of organic carbon. For the with rocks, organic matter occupies the predominalsamples with organic carbon content of 0. 17%and status for gas adsorption power;(2)with the content0.31%, the increase rates of gas generating and ex- variation of organic matter, gas adsorption power maypulsion volume are0 31% and 0. 51%, respectively, vary to several orders; (3) lithology has also certainreflecting the relation between quantitative and quali- effeects onsorption power to some extent. Some gastative changes. Therefore, the value 0. 31% for the adsorption power data on lithology and different ororganic carbon content is a lower limit for marine car- ganic matter are listed in Table 4 18.bonate rocks to generate and expel a large volume of gasTable 4. Effect of lithology and content of organic中国煤化工Max. gas generating volCNMHG C adsorption power(L·t1rock)8419336000Calcareous mudstone23.0024Mudstone4711Mud-beari两数崌215514www.tandf.co.uk/journalsProgressinNaturalScienceVol.15No.92005Considering the experiment results, we think (20 x 108 m.km 2), organic carbon value could bethat the gas adsorption by organic matter cannot be calculated by the formula of gas generating volumeinterpreted only by the principles of adsorption and i.e. the minimal organic matter value for gas generatsuper-critical adsorption. So, we put forward the ing should exceed 20X 10 m.kmprinciple of similitude and solutrope to interpret thegas dissolution action by organic matter and oil gener-The formula of calculating gas generating volumeated in rocksyield of gaseous hydrocarbon, Corg refers to the con-2 Organic carbon value calculated from gas tent of residue organic carbon, V refers to rock volgeneratingume, m refers to rock density( for carbonate rock2.7 gcm 3),K refers to restoration coefficientAs demonstrated by the Ninth"Five-Year State (1.0 is used), and Ig refers to gas generating rateGas Probing Projects and exploring practices, gasBased on the hydrocarbon generating volume per ugenerating potential over 20 X 108 m.km 2 is the nit, the calculated lower limits of organic carbon armain indicator for the forming of large or medium listed in Table 5, varying from 0. 23% to.48%19]n addition, the previous researcheshave acquired some results on the gas generating andThe effective gas expulsion volume equals theexpulsion experiments of carbonate rocks, and lots of sult of gas-generating volume minus loss volume. Duesimulation experiments of carbonate rocks under vari- to the effective gas expulsion volume could be provid-ous experimental conditions have been undertaken in ed by the experiment, so loss volume is not consid-the past years, and the data of gas generating rates ered. It is undoubtful that the high-temperature confor different types of carbonate rocks from various dition in the laboratory has certain expulsion effectseras have been accumulated (Table 5). In accordance on gas expulsion, so the calculated result should bwith the evaluation criteria of gas generating potential the lowest limitTable 5. Gaseous hydrocarbon production rate from simulation experiment and calculated minimal value of organic carbongaseous hydrocarbonCalculated value oforganic carbon(%)RefsLimestone of Majiagou285[20]Limestone of Taiyuan374[21]Limestone of Tieling178Limestone of Xiamalingombustion of245[16]Limestone of Qinglorglass tube2180.393 Analysis of organic carbon in carbonate facies calcareous-strip marls of Upper Ordovicianrocks from four main basins in chinaries of Tazhong 12 Well in Tarim Basin ranges from0. 26% to 2. 17%, with the mean value of 13 samBased on carbonate rock horizons of the four ples at 0. 75%. As to the under-compensation deep-main basins in China, the wells with typical charac- water basin facies mud-bearing limestone, marl,calteristics were selected for the analysis ofcilutite and dolomite sedimented in Tadong 1 Wellbon. Fig. 3 shows the lithologic profiles and colum- the organic carbon content mostly exceeds 2. 0%nar sections of organic carbon content of Tacan 1with the maximal value at 5. 52 %. As to the MedTadong1 and tazhong2 wells located in Tarim un凵中国煤化工 ion lagoon facies mudBasin: Gaoke 1, Wuke 1 wells and Changjianggou bearCNMHGrite and micritic lime-Permian outcrop profile located in Sichuan Basin: stone in" lacan I well, the organic carbon contentDiyu 9, Shancan 1 and Chengchuan 1 wells located in a few samples is as high as 2. 1%, whereas the sourceOrdos Basin; and Konggu 3 Well in North Chinarocks with organic carbon content over 0. 5% are just38 m in thickness方数据 rganic carbon in the lime-moundProgressinNaturalScienceVol.15No.92005www.tandf.co.uk/journals815Depth strateTOC (TOC。%8450=粪Series of Tazhong 12 Well:(b) Tadong 1 Well,4365--4801 3 m: (c)Tacat, huan and Ordos basins, and North China. (a) Upper-OrdovicianSichuan Basin: (f) Changjianggou Permian outcrop profile, Sichuan Basin:(g)OH中国煤化工Bm:(h1 Wellawu se℃tion, Shancan 1 Well, Ordos Basin: (i) Mawu section, Chengchuan 1 Well, OrdoCN MH Gonggu 3 Well, North ChinaWith respect to the Lower-Cambrian and Upper- dolomite is only 0. 10%1.93%, indicating a quiteSinian mudstone and silty mudstone in Gaoke 1 Well, large change. In Wuke 1 Well, the organic carbonSichuan Basin, the maximum content of organic mat- content of Silurian carbonaceous shale is 2. 78%ter reaches /5%3B, while that of limestone and 2.93%, whereas a small number of samples from thewww.tandf.co.uk/journalsProgressinNaturalSciencevoL.15No.92005Cambrian dolosiltite and Ordovician limestone have matter abundance of marine strata is generally lowthe content of 0. 27%0 46%, and most of them In addition, due to the superimposition and transforare below 0.2mation of multi-phase/ time tectonic movements, theeffective Paleozoic source rocks are distributed sparsee mediumiomicrite in the ly, the evolution and characteristics of source rocksangjlanggou Permianprofile, the sourceare inconsistent among blocks, and the reservoirrock strata with organic carbon content exceeding forming conditions are complicated. As a result, the0. 30% take up about one third of the total thickness exploration difficulty and risk are relatively highof strata4 ConclusionsIn Ordos Basin, the organic carbon content ishigh, for which samples were collected from the O(1)In this research, hydrocarbon generatingDiyu 9 Well, and the limestone and expulsion simulation experiment were carried outweathered-crust zone in Shancan 1 Well and Mawu using the samples artificially matched between thesection of Chengchuan 1 Well. With respect to the acid-dissolved residue of relatively low-maturity limecarbonate rock below the weathered crust, the con- stone and the original samples, which makes up fortent is low, and secondary asphalt predominate in or- the insufficiency of source rock samples with highganic matter for the former. With respect to the eval- abundance of organic matters and low maturity inuation of primary hydrocarbon-generating potential China. Organic carbon content of the 10 preparebelow the weathered crust, about a quarter of ordovisamples varies from 0. 15% to.74 %. In accordancecian limestone samples have organic carbon content with the pyrolysis data as well as the hydrocarbonexceeding 0.3%generating and expulsion simulation experiment reThe organic carbon content in the Ordovician tem, the lower limit of organic carbon content forlimestone in Konggu 3 Well in North China is gener- marine carbonate rock to significantly generate andly low (less than 0. 3%), except for a few intervals expel hydrocarbons should be 0. 23%0.31%with higher content due to the infill of secondary as- Moreover, in combination with the numerical analysisphaltof organic carbon in marine carbonate rocks fromTarim, Sichuan, Ordos Basin and North ChinaBased on the comparison results of 10 profiles0.3%could be regarded as the evaluation criterion ofcould be concluded that distribution and hydrocarbon the lower limit of organic carbon content for carbongenerating performance of marine carbonate source ate gas source rocks. With respect to the carbonateocks are closely related with the sedimentary envirock with organic carbon content less than 0. 3%, theronment, which not only controls the lithology and gas generating volume is limited and almost totallyorganic matter abundance, but also affects the elelost, belonging to ineffective gas-generating volumemental composition and hydrocarbon generating po- While for carbonate gas source rock with organic cartential of kerogen. The high-abundance marine source bon content higher than 0. 3%, the gas generatingrocks originated in reduction. Weak reduction envvolume exceeds the loss quantity and reaches the exronment (e. g. under-compensation deepwater basin pulsion threshold, and the gas expulsion volume imfacies, evaporation lagoon facies, etc. could form proves significantly along with the increase of organiccommercial oil/gas pools, such as Weiyuan, Luoimattershai, Wubaiti, Shapingchang, Wolonghe, Dachiganjing, Longmen, Tieshan, Gaofengchang, Xihek(2) The purpose of taking 0. 3%(lower limit ofou, Fuchengzhai and Shuangjiaba gasfields in Sichuan organic carbon content as the evaluation index ofBasirwell as Hetianhe, Jilake and Yakela gas- malYH史中国煤化工facilitate its applicationfields in Tarim Basin. As to the low-abundance ma-inwever, the quantitativerine strata formed in shallow water -extremely shal- evalCNMHGpotential of carbonatelow water platform facies-an oxidization-prone envi- source rocks is dependent on the organic facies zoneronment, no effective gas source rocks would exist formed in the sedimentation of gas source rocks, oxinless the organic carbon content reaches 0.3%dization-reduction conditions during the sedimentarydigenetic process, and the thermal evolution degree布菜据: ina and Ordos basin, the organicetc. Organic facies of restrained marine sedimentationProgressinNaturalScienceVol.15No.92005www.tandf.co.uk/journals817is the most favorable environment for the develop4 Zhao w. Z, Zhang g. Y, He H. Q. et al. Marine Petroleummenof carbonate gas source rocks). The humifica-Geology and the Composite Petroliferous Basin of China. BeijingGeological Publishing House, 2002tion during sedimentary- diagenetic process may de5 Dai J. X, Chen J. F, Zhong N. N. et al. Large Gas Fields andte the organic matter type in carbonate gasTheir Source Rocks in China. Beijing: Science Press, 2003source rock 20. While for highly-evolutional carbon-6 Zai g. M., Wang S. Y, ShiX. Z. et al. Petroleum Geology ofate gas source rocks, the residue organic carbon conChina( vol. 8-12). Beijing: Petroleum Industrial Press,1989-1992tent and hydrocarbon generating potential are reduced7 Dai J.X., Wang T. B. Song Y, et al. Formation and Distribdue to the generation of large-quantity hydrocarbonstion of Medium-Large-Sized Gas Fields in China. Beijing: geologibut the original organic carbon content was higheal Publishing House, 1997than the present one 20Jang d. G, Zhang S. C, Zhang B. M. et alon marine oil generation in China based on Tarim Basin, Earth Sci(3) The evaluation of marine carbonate gasnce frontiers,2000,7(4):534-547hang Y. W., Li G. Y. et al. Enlightenment fromsource rocks is not only related with the original gastroleum geology investigation of Tengiz and Yurubchenskoye cargenerating potential, but also closely related with thebonate oil-gas fields on exploration giant oil-gas fields in Tirumgas generating process and reservoir forming processbasin. Marine Facies Petroleum Geology, 1998, 3(1):49-56During the hydrocarbon generating process of10 Huang D. F, Xiong C. W., Yang J.J. et al. The gas sourcerocks distinguishment and the gas genetic of the middle field in Or-ate rocks, the oil-gas ratio is high, and the hydrocardos Basin. The Natural Gas Industry, 1996,16(6):1-5bon generating history is quite complicated at the bot- 11 Chen A. D. The Ordovician gas origin and migration in the gastom of sedimentary superimposition basins. This willresult in the secondary hydrocarbon generation pro-1994,15(2):1-1012 DaiJ. XF, Wang S. C. et al. Geochemical Feofcess,the forming of paleo-reservoirs, and the gasHydrocarbon Form Coal-Measure, Formation and Resource evalugeneration by oil cracking The forming of paleo-tion of Coal-formed Gas Reservoir in China. Beijing: Petroleum Inreservoirs is an enrichment process for organic matterin marine carbonate source rocks, which makes po3 Dai J. X. Chinas Coal-related Gas Pool Type and the FavourableCoal-related Gas Pespective Areas. Beijing: Petroleum Industrialble the turning of carbonate source rocks into highPress,1986,15-31uality hydrocarbon resources. Moreover, the dual14 Xia X. Y. The Carbonate Rock s Hydrocarbon Formation andattributes of carbonate rock make reservoir carbonateChangqing Gas Field. Beijing: Petroleum Industrial Press, 2000rock turn into a special kind of gas source rocks due to15 Hao S. S, Zhang Y, C. Gang W, Z. et al. The Formation ofOil and Gas in Carbonate Rock. Beijing: Petroleum Industrialthe infill of secondary asphaltPress, 199316 Gao G, Huang Z. L,, Liu G, D. et al. The Simulation ExperiAcknowledgement The anthors are grateful to Lin Peng ment of Petroleum Forming in Carbonate Rock. Beijing: Petroleumand Zhang Zhenling, at RIPED Experimental Center for prepandustrial press, 20ration of the samples, to Prof17 Connan J. Time-temperature relationship in oil genesis. AAPGtute of Geochemistry, CAS, for performing the simulation exBulletin,1974,58:2516-252periment. The data of Tarim Basin, Sichuan Basin and Ordos18 Li J, Hu G. Y, Xie Z. Y. et al. The Study on Gas Accumulation's Physical-chemical Model in Gas Field. Beijing: PetroleumBasin as well as some data of North China are provided by Drndustrial press, 2002Zhang Baomin, Dr. Wang Zecheng, Prof. Qian Kai and Prof19 Dai J.X. Enhance the studies on natural gas geology and find moreCheng Keming at rIPeDlarge gas fields in China. Natural Gas Geoscience, 2003, 65(1)References20 Cheng K. M., Wang Z. Y, Zhong N. N. et al. The Theory andPractice of Gas Forming in Carbonate Rocks. 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