Difference analysis of shale gas-bearing property --A case study of the shale within Lower Cambrian Niutitang Formation on the margin of palaeouplift

Mingna Ge ^1* Shujing Bao ¹ Yufang Wang ¹ Haohan Li ¹ Ting Wang ¹ Hongbo Liang ²

• ¹ Oil and Gas Survey, China Geological Survey, Beijing, China
• ² Research Institute of Petroleum Exploration and Development (RIPED), Beijing, Beijing Municipality, China

Shale gas has become an important field for increasing oil and gas reserves and production in China. The breakthrough of Cambrian shale gas in Sichuan Basin provides guidance for the exploration of shale gas in southern China. However, the Niutitang Formation shale on the periphery of Sichuan Basin exhibits multiple depositional subfacies and complex structural styles, and the factors of gas diversity are not clear. the characteristics of sedimentary facies, structural preservation, shale distribution, organic geochemistry, mineral association, reservoir physical property and gas-bearing are studied by taking the typical wells of Hannan palaeouplift, Shennongjia palaeouplift, Huangling palaeouplift and Xuefengshan palaeouplift in the periphery of Sichuan Basin. The organic matter type of Niutitang Formation shale is mainly type I, the average organic carbon content is 1.50% -3.56%, the average Ro is 2.37% -3.90%, the brittle minerals are mainly quartz that the content is 28% -53%, and the average porosity is 0.51% -3.34%. The pores contain organic pores, inorganic pores and micro-fractures, and the fractures are -2 -mostly filled with calcite. Gas content 0.13m³ /t -4.19m³ /t. Through comparative analysis of main controlling factors affecting gas content of shale, the causes of gas diversity of Niutitang Formation shale are identified. The results show that: (1) the differences in preservation conditions caused by structural strength, fracture development degree and the coupling relationship with tectonic fractures are the key factors restricting the gas content of shale. (2) Early deep burial time, long deep burial time and fast deep burial are the key factors that cause the difference of thermal evolution degree of shale. (3) The difference of hydrocarbon generation potential caused by sedimentary subfacies in the same facies zone is an important factor restricting the gas generation capacity of shale. (4) The areas with good preservation conditions such as the lower Plate of thrust nappe, the degree of thermal evolution is less than 3.0%, and the deepwater facies of trough are favorable directions for further exploration. This study will provides reference significance for shale gas exploration of Cambrian Niutitang Formation in the complex structural area periphery of Sichuan Basin in south China.