Diagenetic facies of the Chang 7 sandstone reservoir in the northern Shaanxi Province, Ordos Basin
Li Wei1,2, Bai Ru3, Ma Yao1, Li Zhaoyu1
1. State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi'an 710069;
2. Xi'an Center of Geological Survey, China Geological Survey, Xi'an 710054;
3. Yanchang Petroleum Research Institute, Xi'an 710075
Based on the comprehensive large numbers of sample test data and field geological investigation, the Chang 7 reservoir have been worked on lithological characteristics, reservoir property and pore structure, diagenesis, diagenetic stage, diagenetic face in Shanbei. The results show that Chang 7 reservoir of the study area is in the stage A to B stage of middle diagenesis phase. Compaction and cementation by carbonate, clay(kaolinite, illite, illite/smectite)mineral and silicon are the main causes of the loss of reservoir primary porosity. Chlorite cementation can prevent the pore from being filled. Dissolution of feldspar improve connectivity between pores. Physical properties of reservoir are improved by these. Six types of diagenetic facies are divided based on diagenesis and their effect on the reservoir quality, Compaction facies, carbonate cementation facies, clay mineral cementation facies and quartz overgrowth facies are unfavorable to the development of high quality reservoir. On the contrary, feldspar dissolution facies and chlorite cementation facies play an important role in improving the physical properties of reservoir.