Pore-Scale Assessment of Gas Expansion Induced by Formation Uplift in Tight Sandstones

Abstract Gas expansion induced by formation uplift plays a crucial role in gas accumulation and secondary reservoir charging. However, in tight sandstones, macroscopic experiments fail to accurately characterize gas saturation changes due to the presence of small pore-throat networks and strong heterogeneity. To address this, we conducted a series of pore-scale analyses, including mercury intrusion, gas adsorption, and NMR, complemented by laser spectrometry and fluid inclusion measurements. Results showed that, as a typical tight sandstone, 87.53% of rigid minerals ensured effective elastic expansion of the reservoir, providing mineral foundation for natural gas expansion. Morphological methods enhanced the full-scale pore-throat radius distribution for various experimental techniques, and the full-scale pore-throat radius distribution based on the T2 spectrum was established by a combined interpolation fitting method. Under the condition of a pressure difference of 8 MPa, the core experiment measured a natural gas expansion averaged rate of 10.98%, confirming from an experimental perspective the formation of natural gas reservoirs caused by formation uplifting. As the pressure difference increased, the contribution of microscopic geological factors to natural gas expansion became more significant. Large pores, homogeneous pore-throats, and abundant clay minerals are effective promoters of natural gas expansion, and the reservoir formation effect of natural gas expansion in the eastern part of the study area is more pronounced. This study provides experimental evidence for the formation of tight gas reservoirs through expansion, and the related results help improve the recovery rate of tight gas and other field work.