Xin YU, Yixiao YANG, Huanhuan ZHOU, Bing LUO, Long LUO, Xin LUO, Yixin ZHU, Weidong CHEN, Shouchun CHEN, Fei LIU, Juanzi YI, Xianfeng TAN, Ruyue WANG, Xun LUO
Lacustrine-delta sandstone of Lianggaoshan Formation has great potential of tight oil and gas resources in eastern Sichuan Basin. It is the key to determine diagenetic evolution and genetic mechanism of tight reservoir distribution prediction. However, genetic mechanism of Lianggaoshan Formation sandstone reservoir was still poorly understood in the eastern Sichuan Basin. Therefore, thin section, X-ray diffraction, scanning electron microscopy, physical property analysis, NMR porosity and high-pressure mercury injection were used to systematically study the petrology, reservoir space, porosity and permeability, and diagenesis. Moreover, genetic evolution mechanism of sandstone reservoir was also systematically analyzed. The main conclusions are as follows: (1) Lianggaoshan Formation sandstone mainly comprise fine-grained lithic sandstone and minor medium-grained and silty lithic sandstone with moderate sorted grains. The reservoir space mainly consists of intergranular dissolved pores, intragranular dissolved pores and primary pores. The porosity ranges from 0 to 8%, and the permeability ranges mainly from 0.001×10-3 μm2 to 0.01×10-3 μm2. (2) Diagenesis mainly includes mechanical compaction, calcite cementation, authigenic chlorite and dissolution. Calcite cements include early pore filling and late replacement of grains. Chlorite mainly occurs as grain coating. The feldspar and calcite cements were main subject of dissolution. (3) The underwater branching channel of high-level system was the mass basis of high-quality reservoir development. Mechanical compaction was the main cause of reservoir densification. The early chlorite coating can protect the pores and provide space for the subsequent precipitation of calcite cementation. The early pore-filling calcite decreased porosity by occupying the pore space. Feldspar and early calcite can produce secondary pore through dissolution. Source rock evolution can provide organic acid and for dissolution. The physical property of reservoirs at the bottom of the sandbody (the main body of sandbody) is better than those in the middle and upper part of the sandbody (the edge of the sandbody). This study can provide important theoretical support for the reservoir prediction.