Main Mechanism for Generating Overpressure in the Paleogene Source Rock Series of the Chezhen Depression, Bohai Bay Basin, China

Abstract

The Chezhen depression, located in the south of Bohai Bay Basin, is an oil-producing basin in China. The third and fourth members of the Shahejie Formation (Es ₃ and Es ₄) are the main source rock series in the Chezhen depression. Widespread overpressures occurred in the Es ₃ and Es ₄ from the depths of approximately 2 000 to 4 600 m, with the maximum pressure coefficient of 1.98 from drillstem tests (DST). Among the sonic, resistivity and density logs, sonic-log is the only reliable pressure indicator and can be used to predict the pore pressure with Eaton’s method. All the overpressured mudstones in the source rock series have higher acoustic traveltimes compared with normally pressured mudstones at a given depth. The overpressured mudstones in the Es ₃ and Es ₄ units are characterized by a normal geothermal gradient, high average density values up to 2.5 g/cm³, strong present-day hydrocarbon generation capability, abundant mature organic matter and high contents of residual hydrocarbons estimated by the Rock-Eval S ₁ values and chloroform-soluble bitumen “A” values. All suggest that the dominant mechanism for overpressure in the mudstones of source rock series in the Chezhen depression is hydrocarbon generation. A comparison between the matrix porosity of the normally pressured sandstones and overpressured sandstones, the quantitative evaluation of porosity loss caused by compaction and the conventional thin section inspection demonstrate that the sandstones in the Chezhen depression were normally compacted. The high contents of hydrocarbons in the overpressured reservoirs prove that the overpressure in the sandstones of the source rock series was caused by pressure transmission from the source rocks.

Keywords

overpressure-generating mechanism / source rock series / Es ₃ and Es ₄ formations / Chezhen depression

References

Anissimov L. Overpressure Phenomena in the Precaspian Basin. Petroleum Geoscience, 2001, 7(4): 389-394.

Berry F. High Fluid Potentials in California Coast Ranges and Their Tectonic Significance. AAPG Bulletin, 1973, 57(7): 1219-1249.

Bethke C. M. Modeling Subsurface Flow in Sedimentary Basins. Geologische Rundschau, 1989, 78(1): 129-154.

Bowers G. L., Katsube T. J. The Role of Shale Pore Structure on the Sensitivity of Wire-Line Logs to Overpressure, In: Huffman, A. R., Bowers, G. L., eds., Pressure Regimes in Sedimentary Basins and Their Prediction. AAPG Memoir, 2002, 76: 43-60.

Chang C. Y. Geological Characteristics and Distribution Patterns of Hydrocarbon Deposits in the Bohai Bay Basin, East China. Marine and Petroleum Geology, 1991, 8(1): 98-106.

Chi G., Lavoie D., Bertrand R., . Downward Hydrocarbon Migration Predicted from Numerical Modeling of Fluid Overpressure in the Paleozoic Anticosti Basin, Eastern Canada. Geofluids, 2010, 10(3): 334-350.

Chilingar G. V., Serebryakov V. A., Robertson J. O. Origin and Prediction of Abnormal Formation Pressures. Elsevier, Amsterdam, 2002.

Deming D. Factors Necessary to Define a Pressure Seal. AAPG Bulletin, 1994, 78(6): 1005-1009.

Dickinson G. Geological Aspects of Abnormal Reservoir Pressures in Gulf Coast Louisiana. AAPG Bulletin, 1953, 37(2): 410-432.

Eaton B. A. Graphical Method Predicts Geopressures Worldwide. World Oil, 1972, 182(1): 51-56.

Espitalié J., Deroo G., Marquis F. La Pyrolyse Rock-Eval et Ses Applications. Troisième Partie. Revue de L'Institut Français Du Pétrole, 1986, 41(1): 73-89.

Guo X. W., He S., Liu K. Y., . Oil Generation as the Dominant Overpressure Mechanism in the Cenozoic Dongying Depression, Bohai Bay Basin, China. AAPG Bulletin, 2010, 94(12): 1859-1881.

Guo X. W., He S., Liu K. Y., . Quantitative Estimation of Overpressure Caused by Oil Generation in Petroliferous Basins. Organic Geochemistry, 2011, 42(11): 1343-1350.

Guo X.W., Liu K.Y., He S., . Quantitative Estimation of Overpressure Caused by Gas Generation and Application to the Baiyun depression in the Pearl River Mouth Basin, South China Sea. Geofluids, 2015, 16(1): 129-148.

Hansom J., Lee M. K. Effects of Hydrocarbon Generation, Basal Heat Flow and Sediment Compaction on Overpressure Development: A Numerical Study. Petroleum Geoscience, 2005, 11(4): 353-360.

Hao F., Dong W. L. Evolution of Fluid Flow and Petroleum Accumulation in Overpressured Systems in Sedimentary Basins. Advance in Earth Sciences, 2001, 16(1): 79-85.

Hao F., Zou H. Y., Gong Z. S. Hierarchies of Overpressure Retardation of Organic Matter Maturation. AAPG Bulletin, 2007, 91(10): 1467-1498.

He S., He Z. L., Yang Z., . Characteristics, Well-Log Responses and Mechanisms of Overpressures within the Jurassic Formation in the Central Part of Junggar Basin. Earth Science—Journal of China University of Geosciences, 2009, 34(3): 457-470.

He S., Song G. Q., Wang Y. S., . Distribution and Major Control Factors of the Present-Day Large-Scale Overpressured System in Dongying Depression. Earth Science—Journal of China University of Geosciences, 2012, 37(5): 1029-1042.

Hermanrud C., Wensaas L., Teige G., . Shale Porosities from Well Logs on Haltenbanken (Offshore Mid-Norway) Show no Influence of Overpressuring. In: Law, B. E., ed., Abnormal Pressures in Hydrocarbon Environments. AAPG Memoir, 1998, 70: 65-85.

Hunt J. M. Generation and Migration of Petroleum from Abnormally Pressured Fluid Compartments. AAPG Bulletin, 1990, 74(1): 1-12.

Jarvis G. T., Mckenzie D. P. Sedimentary Basin Formation with Finite Extension Rates. Earth Planetary Science Letters, 1980, 48(1): 42-52.

Jin Q. Y., He S., Lu M. Relationship between Overpressures Characteristic and Hydrocarbon Enrichment in the Chezhen depression of Bohai Bay Basin. Geological Science and Technology Information, 2015, 34(3): 113-119.

Kukla P. A., Reuning L., Becker S., . Distribution and Mechanisms of Overpressure Generation and Deflation in the Late Neoproterozoic to Early Cambrian South Oman Salt Basin. Geofluids, 2011, 11(4): 349-361.

Law B. E., Spencer C. W. Abnormally High-Pressured, Low-Permeability, Upper Cretaceous and Tertiary Gas Reservoirs, Northern Green River Basin, Wyoming. AAPG Bulletin, 1981, 65(5): 948-948.

Law B. E., Spencer C. W., Bostick N. H. Evaluation of Organic Matter, Subsurface Temperature and Pressure with Regards to Gas Generation in Low-Permeability Upper Cretaceous and Lower Tertiary Sandstones in Pacific Creek Area, Sublette and Sweetwater Counties, Wyoming. The Mountain Geologist, 1980, 17: 23-35.

Lee M. K., Williams D. D. Paleohydrology of the Delaware Basin, Western Texas: Overpressure Development, Hydrocarbon Migration, and Ore Genesis. AAPG Bulletin, 2000, 84(7): 961-974.

Lu K. Z., Qi J. F., Dai J. S., . Tectonic Model of Cenozoic Petroliferous Basin Bohai Bay Province. Geological Publishing House, Beijing, 1997, 3-5.

Lundegard P. D. “Sandstone Porosity Loss—A “Big Picture” View of the Importance of Compaction. Journal of Sedimentary Petrography, 1992, 62(2): 250-260.

Luo M., Baker M. R., Lemone D. V. Distribution and Generation of the Overpressure System, Eastern Delaware Basin, Western Texas and Southern New Mexico. AAPG Bulletin, 1994, 78(9): 1386-1405.

Luo S. Y., He S., Jin Q. Y., . Overpressure System Classification and Structure Characteristic in Bonan Sag. Journal of Jilin University: Earth Science Edition, 2015, 45(1): 37-51.

Luo X. R. The Application of Numerical Basin Modeling in Geological Studies. Petroleum Exploration and Development, 2000, 27(2): 6-10.

Luo X. R., Vasseur G. Geopressuring Mechanism of Organic Matter Cracking: Numerical Modeling. AAPG Bulletin, 1996, 80(6): 856-874.

Luo X. R., Wang Z. M., Zhang L. Q., . Overpressure Generation and Evolution in a Compressional Tectonic Setting, the Southern Margin of Junggar Basin, Northwestern China. AAPG Bulletin, 2007, 91(8): 1123-1139.

Ma B. B., Cao Y. C., Wang Y. Z., . Formation Mechanism of High-Quality Reservoir in the Middle-Deep Strata in Palaeogene in the North Zone of Chezhen Depression. Journal of China University of Mining & Technology, 2014, 43(3): 448-457.

Magara K. Reevaluation of Montmorillonite Dehydration as Cause of Abnormal Pressure and Hydrocarbon Migration. AAPG Bulletin, 1975, 59(2): 292-302.

Meissner F. F. Abnormal Electric Resistivity and Fluid Pressure in Bakken Formation, Williston Basin, and Its Relation to Petroleum Generation, Migration, and Accumulation. AAPG Bulletin, 1976, 60(8): 1403-1404.

Meissner F. F. Petroleum Geology of the Bakken Formation, Williston Basin, North Dakota and Montana. Williston Basin Symposium, 1978, 16(10): 207-227.

Mouchet J. P., Mitchell A. Abnormal Pressures while Drilling: Origins, Prediction, Detection, Evaluation, 1989.

O’Conner S., Swarbrick R., Lahann R. Geologically-Driven Pore Fluid Pressure Models and Their Implications for Petroleum Exploration. Introduction to Thematic Set. Geofluids, 2011, 11(4): 343-348.

Osborne M. J., Swarbrick R. E. Mechanisms for Generating Overpressure in Sedimentary Basins: A Reevaluation. AAPG Bulletin, 1997, 81(6): 1023-1041.

Robertson J., Goulty N. R., Swarbrick R. E. Overpressure Distributions in Palaeogene Reservoirs of the UK Central North Sea and Implications for Lateral and Vertical Fluid Flow. Petroleum Geoscience, 2013, 19(3): 223-236.

Rubey W. W., Hubbert M. K. Role of Fluid Pressure in Mechanics of Overthrust Faulting, II. Overthrust Belt in Geosynclinal Area of Western Wyoming in Light of Fluid-Pressure Hypothesis. AAPG Bulletin, 1959, 70(2): 167-205.

Sharp J. M. Momentum and Energy Balance Equations for Compacting Sediments. Journal of the International Association for Mathematical Geology, 1976, 98(3): 305-322.

Shi W. Z., Chen H. H., Zhang X. M., . Origin of Overpressure and Relation with Oil & Gas Pool-Forming in Yangxia Sag. Earth Science—Journal of China University of Geosciences, 2005, 30(2): 221-227.

Spencer C. W. Overpressured Reservoirs in Rocky Mountain Region. AAPG Bulletin, 1983, 67(8): 1356-1357.

Spencer C. W. Hydrocarbon Generation as a Mechanism for Overpressure in Rocky Mountain Region. AAPG Bulletin, 1987, 71(14): 368-388.

Su J. H., Zhu W., Wei J., . Fault Growth and Linkage: Implications for Tectonosedimentary Evolution in the Chezhen Basin of Bohai Bay, Eastern China. AAPG Bulletin, 2011, 95(1): 1-26.

Suwannasri K., Promrak W., Utitsan S., . Reducing the Variation of Eaton’s Exponent for Overpressure Prediction in a Basin Affected by Multiple Overpressure Mechanisms, 2014

Sweeney J. J., Burnham A. K. Evaluation of a Simple Model of Vitrinite Reflectance Based on Chemical Kinetics. AAPG Bulletin, 1990, 74(10): 1559-1570.

Tingay M. R. P., Hillis R. R., Swarbrick R. E., . Origin of Overpressure and Pore-Pressure Prediction in the Baram Province, Brunei. AAPG Bulletin, 2009, 93(1): 51-74.

van Ruth P., Hillis R., Tingate P., . The Origin of Overpressure in ‘Old’ Sedimentary Basins: An Example from the Cooper Basin, Australia. Geofluids, 2003, 3(2): 125-131.

van Ruth P., Hillis R., Tingate P. The Origin of Overpressure in the Carnarvon Basin, Western Australia: Implications for Pore Pressure Prediction. Petroleum Geoscience, 2004, 10(3): 247-257.

Wang L. B., Xu H. M., Liu T. X. Character of Oil-Gas Accumulation in Double-Layer Structure Basins——Taking Tertiary in Chezhen Sag as an Example. Contributions to Geology and Mineral Resources Research, 2004, 19(2): 118-121.

Xie X. N., Bethke C., Li S. T., . Overpressure and Petroleum Generation and Accumulation in the Dongying Depression of the Bohaiwan Basin, China. Geofluids, 2001, 1(4): 257-271.

Xie X. N., Liu X. F. Related to Black Shale Series Fluid Dynamic System and Relationship with Accumulation of Hydrocarbon in Overpressured Basin. Bulletin of Mineralogy, Petrology and Geochemistry, 2000, 19(2): 103-108.

Yang J., He S., Wang B. J. Characteristics and Prediction Model of the Overpressures in the Niuzhuang Sag of Dongying Depression. Geological Science and Technology Information, 2009, 28(4): 34-40.

Yang R., He S., Li T. Y. Origin of Over-Pressure in Clastic Rocks in Yuanba Area, Northeast Sichuan Basin, China. Journal of Natural Gas Science and Engineering, 2016, 30: 90-105.

Yassir N. A., Bell J. S. Abnormally High Fluid Pressures and Associated Porosities and Stress Regimes in Sedimentary Basins. SPE Formation Evaluation, 1996, 11(1): 5-10.

Zhang J. Z., Bi C. Q., Wang X. F., . Petroleum and Oil Geology and Exploratory Prospect of Chezhen Sag. Offshore Oil, 2005, 25(4): 6-10.

Zheng Z. P., Song G. Q., Liu K. Y. Overpressure Mechanisms in Taoerhe Sag of Chezhen Depression. Geological Science and Technology Information, 2008, 27(6): 71-75.

Zhu G. Y., Jin Q., Zhang S. C., . Hydrocarbon-Generation System of Eogene Shahejie Formation in Chezhen Sag. Natural Gas Industry, 2006, 26(3): 19-22.