Mineralogy and fracture development characteristics of marine shale-gas reservoirs: A case study of Lower Silurian strata in southeastern margin of Sichuan Basin, China

Abstract

Mineral contents and fractures of shale from well Yuye-1 and outcrops were examined mainly based on systematic description of the cores and outcrops, and data from experimental analyses. The data enabled us to thoroughly explore the mineralogy and developmental features of shale of the Lower Silurian Longmaxi Formation in the study area. The results show that, the Lower Silurian Longmaxi Shale (SLS) in the southeastern margin of Sichuan Basin, China, is primarily characterized by a high content of brittle minerals and a relatively low content of clay minerals. The total content of brittle minerals is approximately 57%, including 27% quartz, 12.2% feldspar, 11.2% carbonate and 2.4% pyrite. The total content of clay minerals reaches 41.6%, composed of illite (23.8%), mixed-layer of illite and smectite (I/S) (10.8%) and chlorite (7.0%). The SLS accommodates the widespread development of various types of fractures, including tectonic fractures, diagenetic fractures, inter-layer fractures and slip fractures. The developmental level of the fracture in the SLS is mainly influenced by faults, lithology, mineral contents and total organic carbon content (TOC) in study area.

Keywords

shale fracture / mineralogy / gas shale / Lower Silurian / margin of Sichuan Basin

References

[1] CurtisJ B. Fractured shale-gas systems [J]. AAPG Bulletin, 2002, 86(11): 1921-1938

[2] RossD J, MarcB R. The importance of shale composition and pore structure upon gas storage potential of shale gas reservoirs [J]. Marine and Petroleum Geology, 2009, 26(6): 916-927

[3] ZengL-b, JiangJ-w, YangY-li. Fractures in the low porosity and ultra-low permeability glutenite reservoirs: A case study of the late eocene hetaoyuan formation in the Anpeng Oilfield, Nanxiang Basin, China [J]. Marine and Petroleum Geology, 2010, 27(7): 1642-1650

[4] ShedidS A. Influences of fracture orientation on oil recovery by water and polymer flooding processes: An experimental approach [J]. Journal of Petroleum Science and Engineering, 2006, 50(3): 285-292

[5] BowkerK A. Barnett shale gas production, fort worth basin: Issues and discussion [J]. AAPG Bulletin, 2007, 91(4): 523-533

[6] ZhangC-m, ZhangW-s, GuoY-hai. Sedimentary environment and its effect on hydrocarbon source rocks of Longmaxi Formation in southeast Sichuan and northern Guizhou [J]. Earth Science Frontiers, 2012, 19(1): 136-145

[7] ZengW-t, DingW-l, ZhanfJ-c, ZhangY-q, GuoL, JiuK, LiY-fan. Fracture development in Paleozoic shale of Chongqing area (South China). Part two: Numerical simulation of tectonic stress field and prediction of fractures distribution [J]. Journal of Asian Earth Sciences, 2013, 75: 267-279

[8] JiangZ-x, GuoL, LiangChao. Lithofacies and sedimentary characteristics of the Silurian Longmaxi Shale in the southeastern Sichuan Basin, China [J]. Journal of Palaeogeography, 2013, 2(3): 238-251

[9] WuL-m, DingW-l, ZhangJ-c, LiY-x, ZhaoS, HuL-jun. Fracture prediction of organic-enriched shale reservoir in lower Silurian Longmaxi formation of Southeastern Chongqing Area [J]. Journal of Oil and Gas Technology, 2011, 33: 43-46

[10] JiaQ-p, JiaD, LuoL, ChenZ-x, LiY-q, DengF, SunS-s, LiH-bin. Three-dimensional evolutionary models of the Qiongxi structures, southwestern Sichuan basin, China: Evidence from seismic interpretation and geomorphology [J]. Acta Geologica Sinica (English Edition), 2009, 83(2): 372-385

[11] XuS-l, ChenH-d, ChenA-q, LinL-b, LiJ-w, YangJ-bin. Source rock characteristics of marine strata, Sichuan basin [J]. Journal of Jilin University (Earth Science Edition), 2011, 41(2): 343-350

[12] GuoL, JiangZ-x, ZhangJ-c, LiY-xi. Paleoenvironment of Lower Silurian black shale and its significance to the potential of shale gas, southeast of Chongqing, China [J]. Energy Exploration & Exploitation, 2011, 29(5): 597-616

[13] DingW-l, LiC, LiC-y, JiuK, ZengW-t, WuL-ming. Fracture development in shale and its relationship to gas accumulation [J]. Geoscience Frontiers, 2012, 3(1): 97-105

[14] OlsonJ E, LaubachS E, LanderR H. Combining diagenesis and mechanics to quantify fracture aperture distributions and fracture pattern permeability [J]. Geological Society, London, Special Publications, 2007, 270(1): 101-116

[15] ZhaoZ-y, ZhouY-q, MaX-ming. Study on the similarity of the non-tectonic cracks in mud-shale to underwater shrinkage cracks in present muddy sediments [J]. Journal of Xi’an Shiyou University (Natural Science Edition), 2008, 23(3): 6-12

[16] HeZ-j, LiuB-j, WangPu. Genesis of bedding fracture and its influences on reservoirs in Jurassic, Yongjin area, Junggar Basin [J]. Petroleum Geology and Recovery Efficiency, 2011, 18(1): 15-17

[17] DingW-l, ZhuD-w, CaiJ-j, GongM-l, ChenF-yan. Analysis of the developmental characteristics and major regulating factors of fractures in marine-continental transitional shale-gas reservoirs: A case study of the Carboniferous-Permian strata in the southeastern Ordos Basin, central China [J]. Marine and Petroleum Geology, 2013, 45: 121-133

[18] JarvieD M, HillR J, RubleT E, PollastroR M. Unconventional shale-gas systems: The Mississippian Barnett Shale of north-central Texas as one model for thermogenic shale-gas assessment [J]. AAPG bulletin, 2007, 91(4): 475-499

[19] WeiM-q, DuanY-g, FangQ-t, WangR, YuB-m, YuC-sheng. Mechanism model for shale gas transport considering diffusion, adsorption/desorption and Darcy flow [J]. Journal of Central South University, 2013, 20: 1928-1937

[20] AplinA C, MatenaarI F, VanderP B. Influence of mechanical compaction and chemical diagenesis on the microfabric and fluid flow properties of Gulf of Mexico mudstones [J]. Journal of Geochemical Exploration, 2003, 78: 449-451

[21] CaiQ-p, WuH-w, LuoG-y, HuPing. Influences of pre-existing fracture on ground deformation induced by normal faulting in mixed ground conditions [J]. Journal of Central South University, 2013, 20: 501-509

[22] DorotheaR, JohannaF B, SonjaL P. Fracture systems in normal fault zones crosscutting sedimentary rocks, Northwest German Basin [J]. Journal of Structural Geology, 2012, 45: 38-51

[23] JiuK, DingW-l, HuangW-h, ZhangY-q, ZhaoS, HuL-jun. Fractures of lacustrine shale reservoirs, the Zhanhua Depression in the Bohai Bay Basin, eastern China [J]. Marine and Petroleum Geology, 2013, 48: 113-123

[24] ZengL-b, QiJ-f, WangY-xiu. Origin type of tectonic fractures and geological conditions in low-permeability reservoirs [J]. Acta Petrolei Sinica, 2007, 28(4): 52-56

[25] HillD G, LombardiT E, MartinJ P. Fractured shale gas potential in New York [J]. Northeastern Geology and Environmental Sciences, 2004, 26(1/2): 57-78