Research On Shale Gas Enrichment Regularity Of The Qianfoya Formation In Middle Jurassic In Northern Sichuan, China

Preliminary data and research results show that some shale gas poolinggeological conditions which is belong to the Qianfoya Formation in Middle Jurassicin northern Sichuan are similar to the hydrocarbon source rocks characteristics of theshale gas basins in U.S. And it also has a large shale gas resource potential. However,it deposits in lacustrine environments, and has slightly lower TOC, slightly higherclay minerals and greater burial depth. Therefore, it is necessary to do a more detailedstudy on its reservoir geological conditions and enrichment of shale gas, it is going toplay a guiding role in the next shale gas exploration and breakthrough in northernSichuan. By fully utilizing the measured outcrops, drilling core observationdescription, indoor microscopic thin section identification, previous research datacollection,this paper use the theories such as sedimentology, facies theory of ancientgeography, geochemistry and tectonic sedimentary geology and a variety of test andanalysis technology. It comprehensively studies the Lithostratigraphic, sedimentaryfacies and lithofacies paleogeography, organic geochemistry of hydrocarbon sourcerocks, reservoir characteristics and controlling factors of shale gas enrichment andaccumulation models of the Qianfoya Formation in study area. Main results are asfollows:（1）The rock assemblages of organic-rich shale are mainly gray and black shale,followed by black silty mudstone and black shale of the Qianfoya Formation in studyarea.（2）It deposits in shallow lacustrine and shallow lacustrine-semi-deeplacustrine environments, and deposits underwater distributary channel microfacieslocally of the Qianfoya Formation in northern Sichuan. It also has been established adelta plain-delta front-front delta-Lakeside-shallow lake-semi-deep lake sedimentaryevolution model.（3）Researching on organic geochemical characteristics of hydrocarbon sourcerocks in the area showed its high TOC content, kerogen type to II1, II2, III type-based, high thermal maturity of organic matter. Moreover, the gas-bearing of shale gas iswell.（4）The hydrocarbon source rocks have a moderate brittle mineral contentoverall of the Qianfoya Formation in study area, and owes high clay minerals, whichhave a low I/M relatively, so it has little effect on hydraulic fracturing; Thehydrocarbon source rocks have a good reservoir prmaijioperties in study area, whichporosity and permeability have a positive correlation;Its hole seam types containorganic holes, intergranular pore, mineral mold holes, pores between clay minerals,secondary dissolution pores and cracks, but the main reservoir space types areorganic holes and cracks.（5）Researching reveals that factors including the sedimentary facies,petrographic, cracks are the main controlling reason of high enrichment prolific shalegas of the Qianfoya Formation in study area. It also has established the sedimentaryfacies-lithology-cracks shale gas accumulation model, and preferably out of Zitong-CangXi-Yilong area has a larger exploration potential of the Second Qianfoyasegment in study area.