Determining the segmentation point for calculating the fractal dimension from mercury injection capillary pressure curves in tight sandstone

Abstract

Tight sandstone reservoirs usually exhibit complex pore structure and a high degree of microscopic pore structure heterogeneity. The fractal dimension of pores in tight sandstone calculated by a mercury injection capillary pressure (MICP) curve can be used for the quantitative analysis of pore structure characteristics. The MICP curve of tight sandstone in log–log coordinates can be divided into two straight lines using a segmentation point and the fractal dimension of the pores is calculated in each part. However, the selection of the segmentation point is currently one of the challenges in the studies on the pore fractal characteristics of rocks. The fractal dimensions are calculated based on the non-wetting phase saturation and the wetting phase saturation using the Swanson point, Capillary-Parachor point, and the point at r30 as the segmentation point respectively. The results indicate that the fractal dimension of small pores calculated based on non-wetting phase saturation using the Capillary-Parachor point as the segmentation point best describes the fractal characteristic of pores in tight sandstones. The relationship between the nuclear magnetic resonance transverse relaxation time geometric mean (T2LM) and the fractal dimension of pores verified the efficacy of this fractal dimension calculation method.