INFLUENCE OF MICRO PORE STRUCTURE ON SEEPAGE CAPACITY OF TIGHT SANDSTONE RESERVOIR: A CASE STUDY OF G52 WELL FIELD IN ANSAI OILFIELD

The pore types of reservoirs in the study area are analyzed by conventional thin section, casting thin section (CTS) observation and scanning electron microscopy (SEM) experiments. The characteristics of reservoir pore structure are studied by high pressure mercury injection (HPMI) experiments, and the seepage characteristics of reservoir are analyzed by oil-water relative seepage experiments, then the influence of reservoir pore structure on seepage characteristics is further analyzed. The results show that the pore types in the study area mainly include residual intergranular pores, dissolution pores, intergranular pores and micro fracture, the throat types mainly include necking throats, sheet throats and tube bundle throats. According to the characteristics of high pressure mercury injection capillary pressure curve, the pore structure of the study area can be divided into four types from good to poor: type I similar to IV. The oil-water relative seepage experiments are carried out for the first three types. The results show that the seepage types in the study area can be divided into three types (normal type, linear type and bow-shaped type). Through the analysis of the relationship between pore structure and seepage characteristics, it is found that type I mainly corresponds to the "normal" and "linear" relative permeability curves. Type II and type III corresponds to "bow-shaped", but type II has higher relative permeability of isotonic point compared with type III; The micro pore structure has a certain control effect on the reservoir seepage capacity.