Shale Gas Reservoiring Conditions And Favorable Area Preferred In Lower Paleozoic In Sichuan Weiyuan Area

Along with the increasingly prominent contradiction between supply and demand of energy, oil and gas exploration and development fields gradually towards the direction of coalbed methane, shale gas and other unconventional oil and gas development. The lower Cambrian Qiongzhusi formation and the lower Silurian Longmaxi formation have two sets of high quality marine source rock in Weiyuan of Sichuan Basin.In recent years, shale gas exploration wells in Weiyuan area have been gaining industrial gas flow,showing a good shale gas exploration prospect in Sichuan Basin of the lower Paleozoic. In order to further understand the reservoiring mechanism of shale gas and distribution, this paper titled by "Shale gas reservoiring conditions and favorable area preferred in lower paleozoic in Sichuan Weiyuan area", organic geochemistry, sedimentology, logging geology and reservoiring dynamics theory method were used for systematic study on Marine shale gas accumulation conditions in Weiyuan area, set up a shale gas selection evaluation index system, evaluation method was applied to comprehensive evaluation of advantageous area.Through core observation and logging data analysis, the Weiyuan area Qiongzhusi formation and Longmaxi formation are mainly muddy shallow shelf facies. Effective shale is thick and which distribution is relatively stable, shale organic carbon content is higher, the kerogen type is given priority to with I type, thermal evolution of shale organic is in the over mature stage.Shale siliceous content in Qiongzhusi formation and Longmaxi formation were higher, to facilitate post-fracturing treatment.Well logging, mud logging and core analysis results show that character of shale gas in Qiongzhusi formation and Longmaxi formation is good, free gas and adsorbed gas coexist, muddy gap, organic hole and inorganic mineral intercrystal pores as the main reservoir space, microfracture is the main seepage channel.The shale gas of Qiongzhusi formation and Longmaxi formation reservoir is the thermogenic gas, hydrocarbon gas through the micro cracks in the tectonic stress and pressure of hydrocarbon concentration gradient and gas expansion force after from the piston-displacement type migration. Shale reservoir conditions, and organic carbon content and the cracks that developed from the late tectonic movement have great influence on shale gas formation and distribution scale.According to the shale gas formation conditions and main control factors, to predict shale gas favorable exploration targets blocks in Qiongzhusi formation and Longmaxi formation in Weiyuan area, and have a comprehensive evaluation of the advantageous area from shale gas generate ability, reservoiring ability and preservation conditions.