Study on the Microscopic Pore Structure and Seepage Characteristics of Chang 8 Tight Sandstone Reservoir in Jiyuan Area, Ordos Basin

Abstract

Pore structure and percolation characteristics of reservoir are very important for oilfield development. In this paper, the microscopic pore structure, movable fluid distribution and percolation characteristics of chang 8 tight sandstone reservoir were studied. The influencing factors of microscopic pore structure and seepage characteristics were analyzed. The petrological characteristics, microscopic pore structure, movable fluid distribution and percolation characteristics of the reservoir were analyzed by means of thin section observation, scanning electron microscopy, whole rock analysis, mercury injection experiment, nuclear magnetic resonance and relative permeability experiment. The results show that the reservoir is characterized by fine deviation and moderate sorting. Reservoir relative permeability curve can be divided into three types: (1) oil and water curves both are concave up, (2) oil phase is concave up, and water phase is linear, (3) oil phase is linear, and water phase is concave up. Kaolinite is beneficial to increase the percolation capacity of reservoir. Illite, illite mixed layer and chlorite are not conducive to fluid percolation. The main influencing factors of reservoir percolation characteristics are permeability, pore throat radius, pore throat sorting, pore throat connectivity. The reservoirs with high permeability, large porosity and moderate pore throat distribution have relatively low residual oil saturation, wide oil-water co-seepage area and high oil displacement efficiency in water flooding development. The movable fluid distribution and percolation characteristics of reservoir with different pore structure were compared. By comparing the distribution of movable fluids and relative permeability curve characteristics of reservoirs with different pore structures, mastering the influencing factors of seepage characteristics, and formulating reasonable reservoir development plans for different seepage characteristics reservoir, in order to ultimately improve the reservoirs recovery.