Development characteristics of deepwater gravity flows and tight sandstone reservoir characteristics in Chang 6 in the Huaqing area, Ordos Basin, China

The tight sandstone reservoirs have become the focus of today's oil and gas exploration. To clarify the microscopic characteristics of the tight sandstone reservoirs of the Chang 6(3) deep water gravity flow origin in the Huaqing area, the Chang 6(3) gravity flow origin reservoirs in the study area are divided into three categories. They are the formation reservoir of sandy clastic flow (FROSF), formation reservoir of muddy debris flow deposits and turbidites (FROMT) and formation reservoir of slides and slumps (FROSS). In this study, core and logging data, thin sections, field emission scanning electron microscopy (FE-SEM), and mercury intrusion capillary pressure (MICP) were combined to investigate the rock composition and pore-throat characteristics of tight sandstone reservoirs with different types of gravity flow origins. The reservoir micro-heterogeneity is also investigated in this paper. The results show that the reservoirs with different gravity flow origins are similar in lithology and are mainly composed of feldspar lithic sandstone and lithic feldspar sandstone. The pore types are mainly intergranular pores and feldspar-dissolved pores. There are significant differences in the porosity, permeability, microscopic pore-throat characteristics and microscopic heterogeneity of the reservoirs. From FROSF to FROMT and FROSS, the porosity, permeability, mercury inlet saturation, discharge pressure, median pressure and mercury removal efficiency gradually decrease. The tightness of the reservoir gradually increases. The storage capacity is gradually reduced. The disparity between the throat radius and pore radius gradually increases. The pore-throat structure becomes more complex, and the microscopic heterogeneity of the reservoir gradually increases.