Influence of Tight Sandstone Micro-Nano Pore-Throat Structures on Petroleum Accumulation: Evidence from Experimental Simulation Combining X-ray Tomography

Tight sandstone reservoirs have a special oil-water distribution and oil accumulation characteristics, which are largely attributed to their micro-nano pore-throat structures. This work discusses the influence of tight sandstone micro-nano pore-throat structures on oil accumulation by combining tight sandstone oil accumulation (oil displacing water) experimental simulation, casting thin section and micro-nano X-ray tomography. According to the results, tight reservoirs could be classified into four tight oil accumulation types, where micro pores play a crucial role while the effect of sub micro-nano pores is limited. From type I to IV, the average specific surface of the effective pores, the total throat area, the pore and throat quantity density increase accordingly. On the other hand, their porosity, average coordination number, average pore and throat radii demonstrate a decreasing manner. The effective pore-throat size and configuration control the reservoir minimal migration pressure gradient and the shape of the capillary pressure curve. The larger the peak value of the pore-throat radii lies, the smaller pressure is needed for oil to migrate into the reservoir. And the more uniform the pore-throat radii become, the faster the oil saturation and oil content increase with the pressure gradient.