Study on Genesis of Reservoir Pores of Lower Cretaceous in N Depression

Abstract

The lower Cretaceous reservoirs in N Depression are buried deeply and have strong compaction and cementation, and the oil reservoirs discovered at present are concentrated in the secondary pores. The pore structure and diagenetic evolution of lower Cretaceous sandstone in N Depression are analyzed by using the data of cast thin section, scanning electron microscope, X-ray diffraction and capillary pressure curve, and the main controlling factors of reservoir properties are revealed. The sandstone reservoir has undergone three stages of diagenetic evolution, which are early A, B and middle A. The secondary pore is the main pore structure of sandstone reservoir, which can be divided into two vertical secondary pore zones. The secondary pores mainly include inner pores of dissolved particles, inner pores of dissolved interstitial materials, and so on. The main reasons for the formation of secondary pores are the dissolution caused by atmospheric fresh water leaching, organic acid and clay mineral transformation caused by the thermal evolution of organic matter.