Sedimentary Facies of Marine Shale Gas Formations in Southern China： The Lower Silurian Longmaxi Formation in the Southern Sichuan Basin

• Published in: Journal of earth science (Wuhan, China) Vol. 27; no. 5; pp. 807 - 822
• Main Authors: Li, Yizhen, Wang, Xingzhi, Wu, Bin, Li, Guoqin, Wang, Dule
• Format: Journal Article
• Language: English
• Published: Wuhan China University of Geosciences 01.10.2016; Springer Nature B.V; State Key Laboratory of 0il and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu 610500, China%Chongqing Mineral Resources Development Company Limited,Chongqing 400060, China
• Subjects: Basins; Biogeosciences; Continental shelves; Earth and Environmental Science; Earth science; Earth Sciences; Formations; Gas exploration; Geochemistry; Geology; Geotechnical Engineering & Applied Earth Sciences; Kerogen; Mathematical models; Oil and gas exploration; Oil shale; Organic carbon; Petroleum geology; Porosity; Saturation; Shale gas; Shales; Shelves; Silurian; 下志留统; 含水饱和度; 四川盆地; 地层; 沉积相; 海相; 页岩气; 龙马溪组; China; China, People's Rep; Sichuan Basin; shale gas; continental shelf; Longmaxi Formation; sedimentary facies
• ISSN: 1674-487X; 1867-111X
• DOI: 10.1007/s12583-015-0592-1

Sedimentary facies is an important factor influencing shale gas accumulation. It not only controlls hydrocarbon generation, but also affects reservoir characteristics and distribution. This paper discusses the Lower Silurian Longmaxi Formation in the south of the Sichuan Basin. Outcrop, core, drilling and logging data identify the sedimentary facies of the formation as continental shelf facies, which is divided into two subfacies： an inner shelf and an outer shelf subfacies. These two subfacies can be further divided into seven microfacies： muddy silty shallow shelf, calcareous silty shallow shelf, muddy limy shallow shelf, storm flow, muddy deep shelf, silty muddy deep shelf and contour current microfacies. Vertical and horizontal distribution of microfacies establishes a sedimentation model of the continental shelf facies. Combined with analization or calculation of geochemical, mineralogical, physical and gas-bearing properties of samples, sedimentary microfacies is evaluated using nine parameters： total organic carbon content, effective shale continuous thickness, vitrinite reflectance, kerogen type, mineral components, porosity, permeability, water saturation and gas content. The evaluation revealed that the most favorable facies for shale gas exploration and development are the muddy deep shelf and part of the silty muddy deep shelf microfacies, with TOC more than 2%, siliceous component over 50%, clay less than 30%, porosity more than 3%, water saturation lower than 40%, gas content greater than 2 m3/t. These results provide a theoretical basis for deciston-making on the most promising areas for shale gas exploration in the Sichuan Basin and for marine shale gas exploration and development in South China.