EXPERIMENTAL STUDY ON FRACTAL CHARACTERISTICS OF CONTINENTAL TIGHT SANDSTONE OIL RESERVOIR

The fractal dimension is a parameter that describes the microscopic pore-throat structure of the reservoir based on the space fractal theory. It can be used to reflect the complexity of the pore structure and predict the permeability of the reservoir. In this paper, a systematic fractal study of tight oil reservoirs in the Chang 4+5 Member of Yanchang Formation in the central area of Ordos Basin is conducted based on high-pressure mercury intrusion experiments. The results show that the pore structures of tight sandstone reservoirs have single fractal and multisegment fractal characteristics. Single fractal means that the full aperture has the same fractal characteristics. Multisegment fractal means that pores of different sizes have different fractal characteristics. The pore structure of pores with an average throat radius greater than 0.1 um is more complex and the fractal dimension is larger. This is because the dissolution is stronger in the large pores, while the size of the small pores is more consistent, so the pore structure of the large pores is more complex. Based on fractal theory, it can be found that rock permeability is a function of porosity, pore throat fractal dimension D-f, capillary tortuosity fractal dimension D-t, and maximum pore throat radius. The permeability calculation model based on fractal theory can be used for high-precision quantitative characterization of reservoir permeability.