Coal-Formed Gas Reservoir-Cap Rock Combinations Analysis Of Permian In Zhanhua-Chezhen Sag, Jiyang Depression

The Permian in the Zhanhua-Chezhen sag is the main section of reservoir of coal formed gas. By using high-resolution sequence stratigraphy and sedimenttary,sequences of Permian are recognized,and the reservoir-cap rock combination in the framework of sequence stratigraphy are analysed,On the basis of the detailed study of characteristic and genesis of compactions sand reservoir in the area.The Neopaleozoic strata in the area is divided into 8 sequences. On the basis of stratigraphy architecture,the sedimentary system and depositional microfacies o are analysed in detail,especially the space distribution of sandtone,which exists in the delt depositional system of sequence 4^th and fluvial- lacustrine compositing depositional system,are researched.The physical property and main controlling factors of reservoir are combinedly studied by virtue of log and measured information. The most of compaction sandstone reservoir of Permian is quarz sand,containing much secondary pores and less primary pores.Therefore the reservoir space belongs to the type of pore-crack. And its' physical property is worsening radially outward from the Yihezhuang bulge on plane,and that of Shihezi formation is best on profile. The genesis of tight sand is controlled by the distribution of depositional system and depositional microfacies in early days and diagenesis in the later stage.Reservoir sandstone both qualitatively and qualitatively are estimated by virtue of discriminant analysis of SPSS,and find the reservoir sand of Shihezi formation is best,especially Kuishan section and Xiaofuhe section.Taking reservoir as the main part and cap rock as the secondary part,the reservoir-cap rock combinations are researched. Thus on the basis of reservoir the reservoir-cap rock combinations in the area are divided into 4 types: combinations related to unconformity,highstand systems stract combinations,lowstand systems stract combinations and transgressive systems stract combinations.And among them the combinations related tounconformity,which is reformed later,is good for exploration.