Effect of H2S content on relative permeability and capillary pressure characteristics of acid gas/brine/rock systems: A review

Abstract

Geological storage of acid gas has been identified as a promising approach to reduce atmospheric carbon dioxide (CO 2 ), hydrogen sulfide (H 2 S) and alleviate public concern resulting from the sour gas production. A good understanding of the relative permeability and capillary pressure characteristics is crucial to predict the process of acid gas injection and migration. The prediction of injection and redistribution of acid gas is important to determine storage capacity, formation pressure, plume extent, shape, and leakage potential. Herein, the existing experimental data and theoretical models were reviewed to gain a better understanding of the issue how the H 2 S content affects gas density, gas viscosity, interfacial tension, wettability, relative permeability and capillary pressure characteristics of acid gas/brine/rock systems. The densities and viscosities of the acid gas with different H 2 S mole fractions are both temperature- and pressure-dependent, which vary among the gas, liquid and supercritical phases. Water/acid gas interfacial tension decreases strongly with increasing H 2 S content. For mica and clean quartz, water contact angle increases with increasing H 2 S mole fraction. In particular, wettability reversal of mica to a H 2 S -wet behavior occurs in the presence of dense H 2 S. The capillary pressure increases with decreasing contact angle. At a given saturation, the relative permeability of a fluid is higher when the fluid is nonwetting. The capillary pressure decreases with decreasing interfacial tension at a given saturation. However, the existing datasets do not show a consistent link between capillary number and relative permeability. The capillary pressure decreases with increasing H 2 S mole fraction. However, there is no consensus on the effect of the H 2 S content on the relative permeability curves. This may be due to the limited availability of the relative permeability and capillary pressure data for acid gas/brine/rock systems; thus, more experimental measurements are required.