Shale reservoirs characteristics and favorable areas distribution of the second member of Permian Wujiaping Formation in northeastern Sichuan Basin
The marine shale of the Upper Permian Wujiaping Formation in Sichuan Basin is a hotspot for shale gas exploration and development.Based on X-ray diffraction,thin section identification,scanning electron microscopy,organic geochemistry,and low-temperature nitrogen adsorption,the distribution of sedimentary facies,characteristics of source rocks and reservoirs of the second member of Permian Wujiaping Formation(P2w2)shale in the northeastern Sichuan Basin were conducted.The main controlling factors of reservoir develop-ment were clarified,and distribution of favorable reservoir zones was also analysed.The results show that:(1)The deposition of the P2w2 in the northeastern Sichuan Basin is influenced by the rise of sea level and the development of rifts,and is dominated by deep-water shelf facies,displaying a banded distribution in the areas of Dazhou-Kaijing-Wanzhou-Zhongxian.(2)The mineral composition of the P2w2 shale in the study area is com-plex with a high content of brittle minerals(67.9％).They are similar to the Silurian Longmaxi Formation shale in Sichuan Basin,displaying biogenically influenced quartz with flocculated and framboids pyrite with small grains(＜6 μm),reflecting a reducing sedimentary water body conducive to the enrichment of organic matters.The average porosity of the P2w2 shale is 4.11％,with pore types including organic matter pores,intragranular pores,intergranular pores,and micro-fractures.The shale pore structure is dominated by mesopores,with a minor presence of micropores and macropores,where contribution rate of mesopore to pore volume is the largest.(3)The source rocks of P2w2 exhibit high TOC content and high maturity,with an average TOC content of 4.8％and an average Roof 2.53％,reaching an over-mature stage,predominant type Ⅱ kerogen,indicating high hydrocarbon generation potential.It generally meets the criteria for a Class Ⅰ shale gas reservoirs.(4)P2w2 shale reservoir is mainly controlled by sedimentary environment and diagenetic transformation.The sedimentary envi-ronment of deep-water shelf is conducive to the formation of shale reservoirs.Quartz on resisting pressure and retaining pores,hydrocarbon generation from organic matterrs play a critical role in the formation of shale reservoirs.There is a positively correlated relationship between the quartz content,TOC content to porosity.It is considered that the Kaijiang-Liangping and Wanzhou areas should be favorable distribution areas for the P2w2 shale reservoirs.
shale gasdeep-water shelf faciesreducing environmentbrittle mineralsorganic matter poresthe second member of Wujiaping FormationUpper PermianKaijiang-Liangping areaWanzhou areanortheastern Sichuan Basin
万方数据
维普
