Shiyou shiyan dizhi (Mar 2022)
Geological characteristics and exploration direction of continental shale gas in Jurassic Daanzhai Member, Sichuan Basin
Abstract
Productive breakthroughs have been achieved for the exploration and development of marine shale gas in the Sichuan Basin, and 6 shale gas fields have been built including Fuling, Weiyuan, Changning, Zhaotong, Weirong and Yongchuan. Continental shale gas is an important exploration replacement layer series with great potential. By the approaches of whole rock X-ray diffraction, TOC content, carbon isotope of kerogen, organic petrology, combined determination of high-pressure mercury injection and nitrogen adsorption, argon ion polishing and scanning electron microscope, and physical property test, the formation conditions of shale gas in the Jurassic Daanzhai Member of the Sichuan Basin were discussed, and the main controlling factors of shale gas enrichment were proposed. Results show that continental shale in the Jurassic Daanzhai Member in the Sichuan Basin is featured by rapid lithofacies changes, strong heterogeneity, frequent interbedding of shale, sandstones and limestones, low organic matter abundance, TOC ranging from 0.04% to 3.89% with type Ⅱ2 and Ⅲ of organic matters, low degree of thermal evolution with Ro values ranging from 1.10% to 1.83%, producing both condensate oil and wet gas. Continental shale has high porosity, ranging from 0.95% to 8.42%, There are mainly inorganic mineral pores dominated by micropores and mesopores. The average gas content of field test is 0.96 m3/t. It is clear that semi-deep lacustrine facies, favorable lithofacies assemblage, fractures and preservation conditions are the main controlling factors of continental shale gas enrichment. Based on the analysis of main controlling factors, highlighting the quality and thermal evolution degree of continental shale, combined with preservation conditions and engineering technical conditions, an evaluation criterion of favorable areas for continental shale gas in the Daanzhai Member in the Sichuan Basin was established. Combined with GIS integrated spatial superposition technology, several favorable zones were proposed, including the southwest of Yuanba, the southeast of Langzhong, Yilong, the northwest of Fuling and the northwest of Jiannan areas.
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