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Clay minerals in shales of the Lower Silurian Longmaxi Formation in the Eastern Sichuan Basin, China

  • Geng Yi-Kai (a1), Jin Zhen-Kui (a1), Zhao Jian-Hua (a1) (a2), Wen Xin (a1), Zhang Zhen-Peng (a3) and Wang Yang (a3)...


The present study examines the characteristics of clay minerals in shale gas reservoirs and their influence on reservoir properties based on X-ray diffraction and scanning electron microscopy. These analyses were combined with optical microscopy observations and core and well-log data to investigate the genesis, distribution characteristics, main controlling factors and pore features of clay minerals of the Lower Silurian Longmaxi Formation in the East Sichuan area, China. The clay mineral assemblage consists of illite + mixed-layer illite-smectite (I-S) + chlorite. This assemblage includes three sources of clay minerals: detrital, authigenic and diagenetic minerals. The lower section of the Longmaxi Formation in the Jiaoshiba area has sealing ability which resulted in abnormal high pressures during hydrocarbon generation which inhibited illitization. Therefore, an anomalous transformation sequence is present in which the mixed-layer I-S content increases with depth. This anomalous transformation sequence can be used to infer the existence of abnormal high pressures. The detrital components of the formation also affect the clay-minerals content indirectly, especially the abundance of K-feldspar. The transformation of mixed-layer I-S to illite is limited due to the limited availability of K+, which determines the extent of transformation. Three types of pores were observed in the shale reservoir rocks of the Longmaxi Formation: interparticle (interP) pores, intraparticle (intraP) pores and organic-matter pores. The clay-mineral content controls the development of intraP pores, which are dominated by pores within clay particles. For a given clay mineral content, smectite and mixed-layer I-S were more conducive to the development of shale-gas reservoirs than other clay minerals.


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Anderson, J.L. & Rowley, M.C. (1981) Synkinematic intrusion of peraluminous and associated metaluminous granitic magmas, Whipple Mountains, California. The Canadian Mineralogist, 19, 83101.
Bowker, K.A. (2007) Barnett shale gas production, Fort Worth Basin: Issues and discussion. AAPG Bulletin, 91, 523533.
Buryakovsky, L.A., Rashid, D.D. & Chilingar, G.V. (1995) Abnormally high formation pressure in Azerbaijan and the South Caspian Basin. Journal of Petroleum Science and Engineering, 13, 203218.
Curtis, M.E., Ambrose, R.J., Sondergeld, C.H. & Rai, C.S. (2010) Structural characterization of gas shales on the micro- and nano-scales. SPEPaper 137693 in: Canadian Unconventional Resources and International Petroleum Conference, Calgary, Alberta, Canada.
Daoudi, L., Ouajhin, B. & Rocha, F. (2010) Comparative influence of burial depth on the mineral assemblage of the Agadir-Essaouira Basin (western High Atlas, Morocco). Clay Minerals, 45, 453467.
Desbois, G., Urai, J.L. & Kukla, P.A. (2009) Morphology of the pore space in claystones – Evidence from BIB/FIB ion beam sectioning and cryo-SEM observations. Earth, 4, 1522.
Diaz, E., Sisk, C. & Nur, A. (2010) Quantifying and linking shale properties at a variable scale. ARMA Paper 10- 272. In: 44th U.S. Rock Mechanics Symposium and 5th U.S.-Canada Rock Mechanics Symposium, Salt Lake City, Utah, USA.
Fu, X., Qin, J. & Teng, G. (2011) Mineral components of source rocks and their petroleum significance: A case from Paleozoic marine source rocks in the Middle– Upper Yangtze region. Petroleum Exploration and Development, 38, 671684.
Gao, J., He, S. & Yi, J. (2015) Discovery of high density methane inclusions in Jiaoshiba shale gas field and its significance. Oil and Gas Geology, 36, 472480.
Guo, Y., Li, Z. & Li, D. (2004) Lithofacies palaeogeography of the Early Silurian in the Sichuan area. Journal of Palaeogeography, 6, 2029.
Hillier, S. (1995) Sedimentation and Sedimentary Origin of Clays. Springer-Verlag, Berlin, pp. 162219.
Hower, J. (1981) Shale diageneses. Pp. 6670 in: Clays and the Resource Geologist (Longstrafte, F.J., editor). Short Course Handbook 7, Mineralogical Association of Canada.
Hunt, J.M. (1990) Generation and migration of petroleum from abnormal pressure fluid compartments. AAPG Bulletin, 74, 112.
Jin, N., Li, A. & Liu, H. (2007) Clay minerals in surface sediment of the northwest Parece Vela Basin: distribution and provenance. Oceanologia et Limnologia Sinica, 38, 504511.
Jin, Y., Cai, X., Yuan, Y. & Wu, Y. (2015) Clay mineral characteristics and geological significance in Silurian Longmaxi Formation Shale, southeastern Chongqing. Coal Geology of China, 27, 2125.
Kang, Y., Luo, P. & Jiao, K. (1998) Clay minerals and potential formation damage of tight gas bearing sandstone in West Sichuan. Journal of Southwest Petroleum University, 20, 15.
Khormali, F. & Abtabi, A. (2003) Origin and distribution of clay minerals in calcareous arid and semi-arid soils of Fars Province, southern Iran. Clay Minerals, 38, 511527.
Koster van Groos, A.F. & Guggenheim, S. (1987) Highpressure differential thermal analysis (HP -DTA) of the dehydroxylation of Na-rich montmorillonite and Kexchanged montmorillonite. American Mineralogist, 72, 11701175.
Li, J., Yu, B. & Liu, C. (2012) Clay minerals of black shale and their effect on physical properties of shale gas reservoirs in the southeast of Chongqing: A case study from Lujiao outcrop section in Pengshui, Chongqing. Geoscience, 26, 732740.
Li, Y. & Cai, J. (2014) Effect of smectite illitization on shale gas occurrence in argillaceous source rocks. Petroleum Geology and Experiment, 36, 352358.
Li, Y., Fan, T. & Gao, Z. (2012) Sequence stratigraphy of Silurian Black Shale and its distribution in the southeast area of Chongqing. Natural Gas Geoscience, 23, 299306.
Liang, S., Gan, F., Yan, B. & Wang, R. (2012) Relationship between composition and spectral feature of muscovite. Remote Sensing for Land & Resources, 24, 111115.
Liu, R. (2015) Analyses of influences on shale reservoirs of Wufeng-Longmaxi Formation by overpressure in the Southeastern part of Sichuan Basin. Acta Sedimentologica Sinica, 33, 817827.
Liu, S.G., Wang, S.Y., Sun, W., Ran, B. & Yang, D. (2013) Characteristics of black shale in Wufeng Formation and Longmaxi Formation in Sichuan Basin and its peripheral areas. Journal of Chengdu University of Technology, 40, 621639.
Liu, Y., Di, S. & Xue, X. (1998) Clay minerals from the Lower Cretaccous to Middle Jurassic strata in the Bazhou depression, eastern Qilian folded belt. Journal of Palaeogeography, 18, 1015.
Liu, Y., Yu, B. & Zhu, J. (2009) Diagenesis of Paleogene clastic reservoir in Liaohe River and its influence on reservoir properties. Modern Geology, 23, 731738.
Loucks, R.G., Reed, R.M., Ruppel, S.C. & Jarvie, D.M. (2009) Morphology, genesis, and distribution of nanometer-scale pores in siliceous mudstones of the Mississippian Barnett Shale. Journal of Sedimentary Research, 79, 848861.
Loucks, R.G., Reed, R.M., Ruppel, S.C. & Hommes, U. (2010) Preliminary classification of matrix pores in mudrocks. Gulf Coast Association of Geological Societies Transactions, 60, 435441.
Loucks, R.G., Reed, R.M., Ruppel, S.C. & Hommes, U. (2012) Spectrum of pore types and networks in mudrocks and a descriptive classification for matrixrelated mudrock pores. AAPG Bulletin, 96, 10711098.
Ma, L., Chen, H. & Gan, K. (2004) Tectonic and Marine Petroleum Geology in the South of China. Geological Publishing House, Beijing, pp. 5298.
Miller, C.F., Stoddard, E.F., Bradfish, L.J. & Dollase, W.A. (1981) Composition of plutonic muscovite: Genetic implications. The Canadian Mineralogist, 19, 2534.
Nadeau, P.H., Wilson, M.J., McHardy, W.J. & Tait, J.M. (1985) The conversion of smectite to illite during diagenesis: Evidence from some illitic clays from bentonites and sandstones, diagenesis and lowtemperature metamorphism. Mineralogical Magazine, 49, 393400.
Passey, Q.R., Bohacs, K.M., Esch, W.L., Klimentidis, R. & Sinha, S. (2010) From oil-prone source rock to gasproducing shale reservoir: Geologic and petrophysical characterization of unconventional shale-gas reservoirs. SPE Paper 131350 in: International Oil and Gas Conference and Exhibition, Beijing, China.
Peltonen, C., Marcussen, Ø. & Bjørlykke, K. (2009) Clay mineral diagenesis and quartz cementation in mudstones: the effects of smectite to illite reaction on rock properties. Marine and Petroleum Geology, 26, 887898.
Perry, E.A. & Hower, J. (1970) Burial diagenesis in Gulf coast politic sediments. Clays and Clay Minerals, 28, 165177.
Strixrude, L. & Peacor, D.R. (2002) First-principles study of illite–smectite and implications for clay mineral systems. Nature (London), 420, 165168.
Su, W.B., He, L.Q., Wang, Y.B., Gong, S.Y. & Zhou, H.Y. (2002) The bentonite and high resolution composite formation at the bottom of Wufeng-Longmaxi Formation (Ordovician-Silurian), South China. Science in China (Series D), 32, 207219.
Sun, Y., Yang, F. & Luo, J. (1998) Application of clay minerals in petroleum exploration in Tarim Basin. Modern Geology, 12, 269276.
Wang, S. & Ouyang, Z. (1993) Study on influence of pressure in the dehydration of calcium smectite. Science Bulletin, 28, 243246.
Wang, K., Orth, C.J. & Attrep, M. (1993) The great latest Ordovician extinction on the South China Plate: chemostratigraphic studies of the Ordovician-Silurian boundary interval on the Yangtze Platform Event markers in Earth history. Palaeogergraphy, Palaeoclimatology, Palaeoecology, 104, 6179.
Wang, X., Mou, C. & Gong, Y. (2013) Diagenetic evolution and facies of the reservoir in section 8 of Permian Shihezi Formation He8 section of Z30 block of the Sulige Gas Field. Acta Petrolei Sinica, 34, 883895.
Wang, X., Mou, C. & Ge, X. (2014) Study on clay minerals in the lower Silurian Longmaxi Formation in southern Sichuan Basin and its periphery. Natural Gas Geoscience, 25, 17811794.
Wu, X., Liu, C. & Ju, J. (1997) The identification method of neoformed, inherited and transformed clay minerals. Journal of Xianning Normal College: Science and Technology Edition, 17, 7476.
Yu, H., Xie, J. & Wang, X. (2006) Organoclay complexes in relation to petroleum generation. Earth Science Frontiers, 13, 274281.
Zeng, X., Liu, S. & Huang, W. (2011) Comparison of Silurian Longmaxi Formation shale of Sichuan Basin in China and Carboniferous Barnett Formation shale of Fort Worth Basin in United States. Geological Bulletin of China, 30, 372384.
Zhang, B., Wu, J., Ling, H. & Chen, P. (2010) Petrological discrimination between primary and secondary muscovites and its geological implications: A case study of Fucheng peraluminous granite pluton in southern Jiangxi. Acta Petrologica et Mineralogica, 29, 225234.
Zhang, H., Wang, Q., Ni, K. & Li, C. (2016) Six characteristics and main controlling factors of shale reservoirs in the Wufeng-Longmaxi formations, southeastern Sichuan Basin. Petroleum Geology & Experiment, 38, 320332.
Zhang, Z., Hu, P. & Shen, J. (2013) Mineral compositions and organic matter occurrence modes of Lower Silurian Longmaxi Formation of Sichuan Basin. Journal of China Coal Society, 38, 766771.
Zhang, R. (1992)Application of scanning electronmicroscopy to study of mineral change – transformation of feldspar into clay minerals. Scientia Geological Sinica, 1, 6670.
Zhao, J., Jin, Z., Jin, Z., Wen, X., Geng, Y., Yan, C. & Nie, H. (2016) Lithofacies and sedimentary environment of shale inWufeng–Longmaxi Formation, Sichuan Basin. Acta Petrolei Sinica, 37, 572586.
Zhao, J., Jin, Z., Jin, Z.,Wen, X. & Geng, Y. (2017) Origin of authigenic quartz in organic-rich shales of theWufeng and Longmaxi Formations in the Sichuan Basin, South China: Implications for pore evolution. Journal of Natural Gas Science and Engineering, 38, 2138.
Zhao, X. & He, D. (2008) Clay mineral analysis and some problems of application in petroleum geology. Xinjiang Petroleum Geology, 29, 756758.
Zhou, C., Luo, R. & Li, Z. (2005) The application of scanning electron microscopy in the study of clay minerals in clastic reservoir. Natural Gas Exploration and Development, 28, 48.



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