四川盆地普光地区二叠系大隆组超深层页岩气不同岩相储集空间特征及控制因素OA

Exploratory breakthroughs have been achieved in ultra-deep shale gas from the Permian Dalong Formation in Puguang area of Sichuan Basin.However,due to variable sedimentary environments,diverse lithofacies types,and great burial depths,the pore structure characteristics of different lithofacies remain unclear,which severely constrains subsequent shale gas development.Through experiments on geochemistry,petrology,and pore structure characterization,the reservoir space characteristics and controlling factors of different lithofacies of the Dalong Formation in Puguang area are systematically analyzed.The results indicate:(1)The Dalong Formation mainly develops organic-rich laminated siliceous shale,organic-bearing layered mixed shale,organic-bearing layered calcareous shale,and organic-lean shale.(2)Eight types of reservoir spaces are identified:pores within organic matter,organic matter-matrix pores,intergranular pores between rigid particles,pyrite intercrystalline pores,dissolution pores,intraparticle clay pores,tectonic fractures,and organic matter shrinkage fractures.Compared with other lithofacies,the organic-rich laminated siliceous shale develops larger-scale and more numerous organic pores,dissolution pores,and microfractures,exhibiting higher porosity,pore volume,and proportion of medium-large pores and microfractures.In contrast,organic-lean shale has poorly developed organic pores and microfractures,and inorganic pores are mostly isolated.(3)During the high-maturity thermal evolution stage,most organic matter degrades and is consumed,generating large volumes of oil and gas along with organic pores.Meanwhile,high contents of rigid siliceous minerals(such as feldspar and quartz)can not only provide relatively simple and open large-scale intergranular pores but also release more reservoir space through organic acid dissolution.Therefore,as TOC and siliceous content increase,the corresponding porosity,pore volume,and proportion of medium-large pores and microfractures show an increasing trend.