Research On Shale Gas Reservoir Development Characteristics And Enrichment Regularity Of Da’anzhai Segment In Early Jurassic In Northern Sichuan,China

Research data results show that some shale gas pooling geological conditions which is belong to the Da’anzhai Segment in early Jurassic in northern Sichuan has a large shale gas resource potential. However, it deposits in lacustrine environments, slightly higher clay minerals and greater burial depth. Therefore, it is necessary to do a more detailed study on its reservoir geological conditions and enrichment of shale gas, it is going to play a guiding role in the next shale gas exploration and breakthrough in northern Sichuan. By fully utilizing the measured outcrops, drilling core observation description, indoor microscopic thin section identification, previous research data collection,this paper use the theories such as sedimentology, facies theory of ancient geography, geochemistry and tectonic sedimentary geology and a variety of test and analysis technology. It comprehensively studies the Lithostratigraphic, sedimentary facies and lithofacies paleogeography, organic geochemistry of hydrocarbon source rocks, reservoir characteristics and controlling factors of shale gas enrichment and accumulation models of the Da’anzhai Segment in study area. Main results are as follows:(1) The rock assemblages of organic-rich shale are mainly gray and black shale, followed by black silty mudstone and black shale of the Da’anzhai Segment in study area.(2) It deposits in shallow lacustrine and shallow lacustrine-semi-deep lacustrine environments, and deposits underwater distributary channel microfacies locally of the Da’anzhai Segment in northern Sichuan. It also has been established a delta plain-delta front-front delta-Lakeside-shallow lake-semi-deep lake sedimentary evolution model.(3) Researching on organic geochemical characteristics of hydrocarbon source rocks in the area showed its high TOC content. The kerogen type is mainly in Ⅱ1, Ⅱ2, Ⅲ followed, high thermal maturity of organic matter. Moreover, the gas-bearing of shale gas is well. (4) The hydrocarbon source rocks have a moderate brittle mineral content overall of the Da’anzhai Segment in study area, and owes high clay minerals, which have a low I/M relatively,so it has little effect on hydraulic fracturing; The hydrocarbon source rocks have a good reservoir prmaijioperties in study area, which porosity and permeability have a positive correlation;Its hole seam types contain organic holes, intergranular pore, mineral mold holes, pores between clay minerals, secondary dissolution pores and cracks, but the main reservoir space types are organic holes and cracks.(5) Research reveals the sedimentary facies, lithofacies, fractures and other factors is the main control research area Da’anzhai Segment of shale gas enrichment factors, presumption of Yuanba block in the middle and shallow lake facies and the southern half deep lake and deep lake facies is the Da’anzhai shale gas exploration favorable facies belt.