Investigation on the Pore Structure and Multifractal Characteristics of Tight Sandstone Using Nitrogen Gas Adsorption and Mercury Injection Capillary Pressure Experiments
Bohan Wu, Ranhong Xie, Guowen Jin, Jilong Liu, Shuai Wang, Wenshuai Fan
Abstract
In this paper, we analyze the multifractal characteristics of tight sandstone pore size distributions at different scales through nitrogen gas adsorption and mercury injection capillary pressure experiments. The relationships between the multifractal parameters of the pore size distributions (PSDs), petrophysical parameters (ϕ, k, etc.), and pore structure parameters (SSA, Pd, etc.) are analyzed to characterize the reservoir pore structure. The results reveal that the multifractal parameters of the PSDs can be used to evaluate the reservoir pore structure. The enhancement in the reservoir pore structure complexity is associated with a reduction in k and a increase in Pd, resulting in an increase in ΔD, Δα, and α0 and a decrease in D1, D2, D1/D0, and D2/D0. In addition, the differences in the PSDs obtained from the N2-GA and MICP result in differences in the multifractal characteristics. The high-value measurement area parameters of the N2-GA PSDs can be used to analyze the corresponding multifractal characteristics, but for the MICP PSDs, the low-value measurement area parameters play this role. Furthermore, the pore size of the rock and the amplitude of the MICP PSDs are observed to decrease with increasing clay mineral content. When the reservoir heterogeneity increases, D1/D0 and D2/D0 are reduced and ΔD, Δα, and α0 are enhanced.