Geological characteristics and gas bearing control factors of shale gas in the Wufeng-Longmaxi Formation of the Shaozhai syncline in northeastern Yunnan

A set of organic rich shale with good exploration potential is developed in the Wufeng Formation Longmaxi Formation of the Shaozhai Syncline in northeastern Yunnan; However, its geological characteristics, gas bearing characteristics, and main controlling factors are still unclear. By systematically reviewing previous data and combining with the latest drilling and profile data, the petrological characteristics, organic matter characteristics, reservoir space characteristics, and gas bearing characteristics of organic shale rich in the Wufeng-Longmaxi Formation of the Shaozhai Syncline were analyzed, and the controlling factors of gas bearing properties were discussed. The results show that the Wufeng-Longmaxi Formation in the Shaozhai Syncline is a shallow water shelf deep water shelf deposit, with a thickness of organic rich shale ranging from 35 to 105m; The organic rich shale in the upper section of the Wufeng Formation and the lower section of the Longmaxi Formation has a high TOC content, mostly above 2%, with good organic matter types and good hydrocarbon generation potential; High quality shale has a high content of brittle minerals and good fracturing performance. There are multiple types of reservoir spaces, including shale gas storage pores mainly composed of organic matter pores, intergranular pores, and intra particle pores, as well as mineral fractures and interlayer fractures of clay minerals that communicate with fracturing channels and macroscopic fractures. The gas content of shale in the study area varies greatly. The gas content in the Gaoqiao area is relatively high, but the CH4 air free base content is low. The gas content in the Lianfeng area is relatively low, but the CH4 air free base content is high, both of which are above 95%. The study found: the difference in total gas content of shale at the same structural location is controlled by TOC content， pore volume, pore specific surface area, clay mineral content, pyrite content, and carbonate mineral content. The shale gas content at different structural locations is controlled by the sedimentary environment and preservation conditions under structural control. The deep water continental shelf, wide and gentle synclines far from major faults and with fold shielding under structural control have better gas bearing properties, it is a favorable area for shale gas enrichment in the study area.