Reservoir characteristics and main controlling factors of Yingcheng-Shahezi formations in southeast ramp region of Lishu Fault Depression, Songliao Basin

The sandstone reservoirs of the Lower Cretaceous Yingcheng-Shahezi formations in the Lishu Fault Depression of the Songliao Basin have a strong heterogeneity and a low exploration success rate. Through core observation, thin section identification and quantitative statistics, porosity and permeability analysis, mercury intrusion, etc., it was concluded that the Yingcheng-Shahezi formations in the southeast ramp of Lishu Fault Depression are dominated by pebbly sandstones, followed by fine-grained and medium-grained sandstones, with low contents of coarse debris and quartz, and low compositional and structural maturities. The main components are feldspathic lithic sandstones, lithic sandstones, and lithic feldspar sandstones, with a small amount of feldspar sandstones. Feldspars and rock debris are in high content, and the interstitial material is mainly argillaceous and calcite. The Yingcheng-Shahezi formations have an ultra-low porosity and an ultra-low permeability with a strong heterogeneity. They consist of primary intergranular pores, secondary dissolved pores and fissures, mainly primary pores, and fractures in some areas. The pore development of reservoirs is controlled by sedimentary environment and diagenesis, and the role of late tectonic fractures cannot be ignored. The primary pores were greatly reduced by cementation and mechanical compaction, while dissolution and structural rupture effectively improved the physical properties of the reservoir. In particular, the late tectonic fissures produced different types of fractures and increased porosity and permeability, which may be one of the important reasons for the formation of high-yield oil and gas fields in the Qinjiatun and Jinshan areas of the southeast ramp.