Determination of Time of Oil Cracking into Gas in Weiyuan Paleo-Oil Pool in Sichuan Basin, South China

Document Type : Research Paper


Petroleum Exploration and Production Research Institute, SINOPEC, Beijing, China


Weiyuan gas field, located in the Sichuan basin of south China, is a large marine gas field with the oldest reservoir (the Sinian sequences) in south China. The hydrocarbon origin of the gas field has long been debated by petroleum geologists. Recently, it was recognized that a paleo-oil pool maybe the significant contributor to the gas field. Consequently, when the paleo-oil pool had been cracked into gas has become an interesting topic. Actually, the time determination of oil cracking into gas is of significance to marine gas reservoir exploration in south China, because it is a pervasive hydrocarbon resource of marine gas reservoirs in south China. Characteristics of the gas composition, fluid inclusion, and bitumen in Sinian reservoir show that the present-day Weiyuan gas field originates from a paleo-oil pool cracked at high temperature. Data collected from the previous documents show that the temperature window of oil cracking into gas is around 160 to 210 °C on a geological time scale. On the basis of vitrinite reflectance, the heat flow history and erosion thickness in Weiyuan area were reconstructed. With the combination of heat flow history and burial history, the temperature history the paleo-oil pool experienced was reconstructed. The time of the paleo-oil cracking into gas is determined according to the oil cracking temperature window. The results show that the oil in the Weiyuan Sinian paleo-oil pool cracked into gas during the late Triassic to Eocene age.


     [1].    Cai L., Rao D., and Pan W., “The Evolution Model of the Puguang gas Field in Northeast of Sichuan,” Petroleum Geology & Experiment, 2005, 27, 462-467.##
     [2].    Wang S., Zhen B., and Cai L G., “Fossil Oil Pool and Petroleum Assessment in South China,” Marine Origin Petroleum Geology, 1997, 2, 44-50.##
     [3].    Jin Z. and Cai L., “Exploration Prospects, Problems, and Strategies of Marine Oil and Gas in China,” Oil & Gas Geology, 2006, 26, 721-730.##
     [4].    Jin Z., “Particularity of Petroleum Exploration on Marine Carbonate Strata in China Sedimentary Basins,” Earth Science Frontiers, 2005, 12, 15-22.##
     [5].    Geng X. and Geng A., “Kinetic Simulating Experiment on Secondary Thermal Cracking of the Bitumen Generated from Marine Carbonate Rock,” Natural Gas Geoscience, 2008, 19, 695-700.##
     [6].    Ma Y., Cai X., and Guo T., “Main Controlling Factors of Oil and Gas Filling and Enrichment of the Puguang Large Gas Field in Sichuan Basin,” Chinese Science Bulletin, 2007, 54, 149-155.##
     [7].    Sweeney J. J. and Burnham A. K., “Evaluation of a Simple Model of Vitrinite Reflectance Based on Chemical Kinetics,” AAPG Bulletin, 1990, 74, 1559-1570.##
     [8].    Jia C. Z., Wei G. Q., and Li B. L., “Tectonic Evolution of Two-epoch Foreland Basins and its Control for Natural Gas Accumulation in China’s Mid-western Areas,” Acta Petrolei Sinica, 2003, 24, 13-17.##
     [9].    Wei G., Chen G., and Du S., “Petroleum Systems of the Oldest Gas Field in China: Neoproterozoic Gas Pools in the Weiyuan Gas Field, Sichuan Basin,” Marine and Petroleum Geology, 2008, 25, 371-386.##
   [10].   Xu H. L., Wei G. Q., and Jia C. Z., “Tectonic Evolution of the Leshan-Longnvsi Paleo-uplift and its Control on Gas Accumulation in the Sinian Strata, Sichuan Basin,” Petroleum Exploration and Development, 2012, 39, 406-416.##
   [11].   Wei L., Haiyong Y., and Wangshui H., “Tectonic Evolution of Caledonian Palaeohigh in the Sichuan Basin and its Relationship with Hydrocarbon Accumulation,” Natural Gas Industry B, 2014, 1, 58-65.##
   [12].   Song W., “New Insights in the Caledonian Paleouplift in Sichuan Basin,” Natural Gas Industry, 1987, 6, 6-11.##
        [13].       Yang J., “Study on Formation and Evolution of Sinian Petroleum Pools in Leshan-Longnusi Paleo-uplift,” Sichuan Basin, Chengdu, China: Southwest Petroleum College, 2002.##
   [14].   Xu Y., Shen P., and Li Y., “The Oldest Gas Pool of China Weiyuan Sinian Gas Pool, Sichuan Province,” Acta Sedimentologica Sinica, 1989, 7, 3-13.##
   [15].   Yin C., Wang T., and Wang S., “Differences between Kerogen and Oil-cracked Gases in Sinian Reservoirs of Weiyuan and Ziyang Area,” Acta Sedimentologica Sinica, 2001, 19, 156-160.##
        [16].       Sun W., Liu S. G., and Ma Y. S., “Determination and Quantitative Simulation of Gas Pool Formation Process of Sinian Cracked Gas in Weiyuan-Ziyang Area Sichuan Basin,” Acta Geologica Sinica, 2007, 81, 1153-1159.##
   [17].   Yuan Y. S., Sun D. S., and Zhou Y., “Relationship between Hydrocarbon Generation History of Source Rocks and Sealing History of Mudstone Cap-rocks in the Southeast Sichuan Basin,” Geological Review, 2010, 56, 831-838.##
   [18].   Prinzhofer A. A. and Huc A. Y., “Genetic and Post-genetic Molecular and Isotopic Fractionations in Natural Gases,” Chemical Geology, 1995, 126, 281-290.##
   [19].   Cui H., Zhang L., and Wei G., “Characteristics of the Sinian Reservoir Bitumen in Weiyuan-Ziyang Areas of the Sichuan Basin and its Significance,” Petroleum Geology & Experiment, 2008, 30, 489-493.##
   [20].   Xie Z., Tian S., and Wei G., “The Study on Bitumen and Foregone Pool of Feixianguan Oolitic in Northeast Sichuan Basin,” Natural Gas Geoscience, 2005, 16, 283-288.##
   [21].   Price L. C., “Thermal Stability of Hydrocarbons in Nature: Limits, Evidence, Characteristics, and Possible Controls,” Geochimica et Cosmochimica Acta, 1993, 57, 3261-3280.##
   [22].   Behar F. and Vandenbroucke M., “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, 1996, 10, 932-940.##
   [23].   Schenk H. J., Di Primio R., and Horsfield B., “The Conversion of Oil into Gas in Petroleum Reservoirs. Part 1: Comparative Kinetic Investigation of Gas Generation from Crude Oils of Lacustrine, Marine and Fluviodeltaic Origin by Programmed-temperature Closed-system Pyrolysis,” Organic geochemistry, 1997, 26, 467-481.##
   [24].   Guo L., Tian H., and Jin Y., “Reaction Mechanism, Medium Influencing Factors and Identification and Evaluation of Oil-cracking Gas,” Geochemica, 2008, 37, 499-511.##
   [25].   Zhao W., Wang Z., and Zhang S., “Oil Cracking into Gas is an Important Way for Marine Gas Resource Kitchen,” Chinese Science Bulletin, 2006, 51, 589-595.##
   [26].   Zieglar D. L. and Spotts J. H., “Reservoir and Source-bed History of Great Valley, California,” AAPG Bulletin, 1978, 62, 813-826.##
        [27].       Neglia S., “Migration of Fluids in Sedimentary Basins,” AAPG Bulletin, 1979, 63, 537-597.##
   [28].   Tissot B. P., Pelet R., and Ungerer P., “Thermal History of Sedimentary Basins, Maturation Indices, and Kinetics of Oil and Gas Generation,” AAPG Bulletin, 1987, 71, 1445-1466.##
   [29].   Claypool G. E. and Mancini E. A., "Geochemical Relationships of Petroleum in Mesozoic Reservoirs to Carbonate Source Rocks of Jurassic Smackover Formation, Southwestern Alabama,” AAPG Bulletin, 1989, 73, 904-924.##
   [30].   Evamy B. D., Haremboure J., and Kamerling P., “Hydrocarbon Habitat of Tertiary Niger Delta,” AAPG Bulletin, 1978, 62, 1-39.##
   [31].   Yun L. and Zhai X., “Discussion on Characteristics of the Cambrian Reservoirs and Hydrocarbon Accumulation in Well Tashen-1, Tarim Basin,” Oil & Gas Geology, 2008, 29, 726-732.##
   [32].   Hunt J. M., “Petroleum Geochemistry and Geology,” New York: W H Freeman, 1996.##
   [33].   Ping H., Chen H., and Song G., “Oil Cracking of Deep Petroleum in Minfeng Sag in North Dongying Depression, Bohai Bay Basin, China: Evidence from Natural Fluid Inclusions,” Journal of Earth Science, 2010, 21, 455-470.##
   [34].   Schenk H. J. and Dieckmann V., “Prediction of Petroleum Formation: the Influence of Laboratory Heating Rates on Kinetic Parameters and Geological Extrapolations,” Marine and Petroleum Geology, 2004, 21, 79-95.##
        [35].       Dieckmann V., Schenk H. J., and Horsfield B., “Kinetics of Petroleum Generation and Cracking by Programmed-temperature Closed-system Pyrolysis of Toarcian Shales,” Fuel, 1998, 77, 23-31.##
   [36].   Pepper A. S. and Dodd T. A., “Simple Kinetic Models of Petroleum Formation: Part 2: Oil-gas Cracking,” Marine and Petroleum Geology, 1995, 12, 321-340.##
   [37].   Horsfield B., Schenk H. J., and Mills N., “An Investigation of the in-reservoir Conversion of Oil to Gas: Compositional and Kinetic Findings from Closed-system Programmed-temperature Pyrolysis,” Organic Geochemistry, 1992, 19, 191-204.##
   [38].   Tian H., Xiao X., and Li X., “Comparison of Gas Generation and Carbon Isotope Fractionation of Methane from Marine Kerogen and Crude Oil-cracking Gases,” Geochemical, 2007, 36, 71-77.##
   [39].   Zhao W., Wang Z., and Wang Z., “Progresses and Significances of Research on High-efficiency Gas Reservoir Formation in China,” Earth Science Frontiers (China University of Geosciences, Beijing/Peking University), 2005, 12, 499-506.##
   [40].   Dai J X., “Pool-forming Periods and Gas Sources of Weiyuan Gasfield,” Petroleum Geology & Experiment, 2003, 25, 473-480.##
   [41].   Yuan Y. S., Zheng H. R., and Tu W., “Methods of Eroded Strata Thickness Restoration in Sedimentary Basins,” Petroleum Geology & Experiment, 2008, 30, 636-642.##
        [42].       Zhang W., Sun Z., and Li W., “Paleogeothermal Modeling using Thermodel for Windows System with Case Study,” Journal of East China Institute of Technology, 2005, 28, 341-346.##
   [43].   Springer J., “Decompaction and Backstripping with Regard to Erosion, Salt Movement and Interlayered Bedding,” Computers & Geosciences, 1993, 19, 1115-1125.##
        [44].       Tang J., Zhang T., and Bao Z., “Study of Organic Inclusion in the Carbonate Reservoir Bed of the Weiyuan Gas Field in the Sichuan Basin,” Geological Review, 2004, 50, 210-214.##