Study on pore structure characteristics of tight sandstone in Block 4 of the central Junggar Basin

The pore structure of tight sandstone is the major factor affecting physical property, performance and seepage characteristics of reservoir. The accurate characterization of rock pore structure is one of the important contents of reservoir evaluation. Therefore, the pore structure characteristics of tight sandstone reservoir in Well Dong-11, Block 4, central Junggar Basin were studied qualitatively and quantitatively through core observation, CT scanning imaging and image processing. The results show that:USM sharpening, threshold selection and median filtering were used for image processing of gray scale images in micro-CT scanning, which could better distinguish the boundary between skeleton and pore inside the rock and improve the image segmentation accuracy. Porosity tends to be constant when the side length of the digital core cube model is 450 voxel. The reservoir space of tight sandstone reservoirs in the study area is mainly composed of intergranular pores and micro-fractures, with a small number of cleavage fractures, and more isolated pores. Pores are characterized by complex shapes and uneven distribution. The porosity distribution of the continuous section of the tight sandstone in the study area is not uniform and highly discrete. The maximum and minimum values of porosity appear frequently on continuous sections (strong jumping), which is easy to cause excessive pressure drop in the process of fluid flow, resulting in partial pore throat blockage. The pore size distribution of tight sandstone reservoir in the study area is not uniform. The pore diameter is mainly from 15 microns to 35 microns, which accounts for about 60% of the total pore number, but its area only accounts for 18%. The pores take up 20% of the total number of pores from 50 microns to 200 microns in diameter, but the area takes up 60%, which provides favorable storage space for oil and gas.