Abstract:

In order to find out effective reservoirs in Xinchang area, western Sichuan Basin, the data of rock slices, casting slices, scanning electronic microscope and micro-CT scanning, as well as reservoir physical properties, were used to discuss the characteristics of petrologic features, reservoir spaces, pore types and diagenesis of tight sandstone reservoir of the fifth member of Xujiahe Formation. The results show that the tight sandstone is mainly of lithic sandstone and lithic quartz sandstone. The porosity of the reservoir is low and the reservoir is super tight. Reservoir space consists of nano intergranular pores, micron dissolved pores and micro cracks of different genesis, among which the intergranular pores are the main reservoir space. According to the micro-CT scanning results, the abundance of organic matter in the sandstone controls the development and distribution of pores, and the porosity increases with the raise of the abundance of organic matter. The shape and distribution of micro pores affect reservoir connectivity, and the connectivity rate of concentrated micro pores is superior to scattered micro pores. Compaction, replacement and cementation are the major causes of density of reservoir. Dissolution has a certain positive impact on improving the physical properties of reservoir, but makes little change of porosity.

Key words:  illite , kaolinite , authigenic clay minerals , hydrothermal alternation , Taiyuan Formation , eastern Ordos Basin