Influence of Acid Treatment on Pore Structure and Fractal Characterization of a Tight Sandstone: A Case Study from Wudun Sag, Dunhuang Basin

Abstract

In this study, X‐ray diffraction, N2 adsorption (N2A), and mercury intrusion (MI) experiments were used to investigate the influence of acid treatment on pore structure and fractal characterization of tight sandstones. The results showed that acid treatment generated a certain number of ink‐bottle pores in fine sandstone, aggravated the ink‐bottle effect in the sandy mudstone, and transformed some smaller pores into larger ones. After the acid treatment, both the pore volume in the range of 2–11 nm and 0.271–8 μm for the fine sandstone and the entire pore size range for the sandy mudstone significantly increased. The dissolution of sandstone cement causes the fine sandstone particles to fall off and fill the pores; the porosity increased at first but then decreased with acid treatment time. The fractal dimension obtained using the Frenkel‐Halsey‐Hill model was positively correlated with acid treatment time. However, the total fractal dimensions obtained by MI tests showed different changes with acid treatment time in fine sandstone and sandy mudstone. These results provide good guiding significance for reservoir acidification stimulation.

Geochemical reactions altering the mineralogical and multiscale pore characteristics of uranium-bearing reservoirs during CO2 + O2in situ leaching

“…Specifically, the total pore volume contribution rates of the micropore, transition pore, and mesopore of coarse sandstone, medium sandstone, fine sandstone, siltstone, and sandy mudstone reduce from 22.517%, 23.296%, 35.778%, 22.119%, 85.067% to 6.452%, 6.594%, 21.432%, 4.545%, and 75.116%, respectively, while the pore volume contribution rate of the macropore of coarse sandstone, medium sandstone, fine sandstone, siltstone, and sandy mudstone improves from 77.483%, 76.703%, 64.222%, 77.881%, 14.933% to 93.548%, 93.406%, 78.568%, 95.455%, and 24.882%, respectively. This knowledge is consistent with the studies conducted by Zhou et al ( 2021) and Geng et al (2022) because the reaction environment and rock lithology are analogous; however, Li H. et al (2020) found that the supercritical CO 2 treatment can increase the micropore volume and connectivity in granite, which is contradictory to this study because the mineral constituent in the samples shows a large difference. This indicates that the CO 2 + O 2 -water-rock geochemical reaction first affects the mineral composition and spatial distribution, and the full-scale pore structure is varied immediately.…”