Characterization of Microscopic Pore Structure and its Effect on Macroscopic Physical Parameters in Tight Gas Reservoirs

A combination of mercury intrusion capillary pressure (MICP) and N adsorption experiments were performed on tight rock samples from the Shahezi formation in Xujiaweizi Default Depression in order to detect the applicability of the two techniques for characterizing the complete pore size distribution and gaining insight into the microscopic pore structure and its effect on macroscopic physical parameters. N adsorption and MICP measurements were used to analyze the pore size distribution of mesopores and macropores respectively. The result shows that tight gas reservoirs are characterized by complicated microscopic pore structure with a broad pore size distribution from 2nm to 200μm. The dominant pores range from 10nm to 2μm, which mainly consist of slit-shaped pores and ink-bottle shaped pores. Porosity, permeability and free fluid saturation decrease with the increase of the volume proportion of small pores (diameter< 50nm), and increase with the increase of the volume proportion of large pores (diameter>200nm). Furthermore, the relationship between the volume proportion of different pores and permeability and free fluid saturation is better than that with the porosity.