Analysis of pore type and micro pore structure of reservoir in fault basin--Taking Wuerxun depression as an example

Wuerxun depression is the two main oil-bearing depressions in Hailaer basin. Nantun Formation of Wuerxun depression is the most important oil-gas exploration layer, and reservoir characteristics are the main factors controlling oil-gas enrichment. In this paper, the mineral composition and pore type of Nantun Formation reservoir are analyzed by XRD and SEM. It is clear that the main rock types are lithic sandstone and feldspar lithic sandstone. As a whole, it is compact, with poor connectivity of pores and coexistence of primary and secondary pores. Primary pore is mainly residual primary intergranular pore, and secondary pore is the main reservoir space of Nantun Formation, which lays a foundation for further oil and gas exploration. The rock types of the target layer in the study area are mainly lithic sandstone and feldspathic lithic sandstone. Among them, Tongbomiao formation in Wuerxun depression is dominated by conglomerate, while sandstone in Nantun Formation is mainly lithic arkose and feldspathic lithic sandstone; sandstone in Tongbomiao formation and Nantun Formation in Beier depression is dominated by lithic sandstone and feldspathic lithic sandstone. The rocks of Nantun Formation are compact as a whole, with poor connectivity of pores and coexistence of primary and secondary pores. The primary pores are mainly residual primary intergranular pores, mainly of three types. Secondary pore is the main reservoir space of Nantun Formation, including dissolution intergranular pore, dissolution intergranular pore, interstitial matter dissolution pore, intergranular micro pore and micro fracture of authigenic minerals, among which intergranular dissolution pore is the most developed and super large dissolution intergranular pore is the main one.