庆城南—合水南地区长7湖底扇致密砂岩储层质量差异研究OA

The Triassic Yanchang Formation in the Ordos Basin,as an important target for exploration and development of tight reservoirs in the sublacustrine fan,is currently a research hotspot of continental lacustrine basins.This paper takes the tight sandstone reservoirs of the Chang 7 sublacustrine fan in the southern Qingcheng and southern Heshui area as the research object,and based on extensive core analysis and logging data,conducts a study on the difference of matrix reservoir quality controlled by sedimentation and diagenesis.The quality of the Chang 7 tight sandstone reservoirs in the study area can be classified from good to poor into types Ⅰ1,Ⅰ2,Ⅱ,and Ⅲ.Among them,the relatively high-quality type Ⅰ1 reservoirs are mainly characterized by large intergranular pores and flake-like/constriction throats,with porosity mainly greater than 10％.The type Ⅰ2 reservoirs are mainly characterized by medium intergranular pores and plate-like throats,with porosity mainly ranging from 8％to 10％.Compaction is the key factor for the tightness of the tight sandstone reservoirs in the study area.The larger the grain size of the tight sandstone reservoirs,the smaller the destructive effect of compaction on the reservoir quality.The Chang 7 tight sandstone reservoirs in the study area are mainly cemented by carbonates,with stronger cementation in the sand-mud interface near the sandstone,and high matrix content weakens the cementation in the early diagenesis.Dissolution has an important constructive effect on the Chang 7 tight sandstones.To a certain extent,increased porosity by dissolution is negatively correlated with the matrix content.The type Ⅱ reservoirs are the main type in the Chang 7 tight sandstone reservoirs in the study area.Type Ⅰ1 and Ⅰ2 reservoirs are mainly distributed in the middle of the branch channels and lobe sand bodies.Type Ⅱ reservoirs mostly develop within the lobe sand bodies.Type Ⅲ reservoirs are primarily developed at the top and bottom of the branch channels and lobe sand bodies,as well as in some thin lobe sand bodies and along the edges of lobes.