Pore Structure and Multifractal Characteristics of Tight Sandstone: A Case Study of the Jurassic Sangonghe Formation in Northern Turpan-Hami Basin, NW China

Pore structure and multifractal characteristics are two critical indicators for evaluating the heterogeneity of tight sandstone reservoirs. An integrated analysis comprising physical property tests, X-ray diffraction, casting thin sections, scanning electron microscopy, high-pressure mercury intrusion (HPMI), and constant-rate mercury intrusion (CRMI) is conducted on five samples from the Jurassic Sangonghe Formation in the northern Turpan-Hami Basin to investigate the full-scale pore size distribution (FPSD) and its multifractal characteristics. The results indicate that the pores in tight sandstone are mainly residual intergranular pores, dissolution pores, intercrystalline pores, and microfractures. The FPSD exhibits a bimodal or trimodal pattern, with dominant pore sizes ranging from 0.00516 μm to 1.15 μm. Two key multifractal parameters, the multifractal dimension range (Dmin−Dmax) and the relative dispersion (Rd), were utilized to effectively characterize pore structure heterogeneity and asymmetry. Higher Dmin−Dmax values correspond to stronger heterogeneity, whereas lower Rd values indicate a dominance of nanoscale pores. Furthermore, Dmin−Dmax and Rd exhibit negative correlations with permeability and clay mineral content, and positive correlations with feldspar content. This study demonstrates the utility of FPSD in characterizing pore structure and highlights the applicability of multifractal theory in assessing the heterogeneity of tight sandstone reservoirs.