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 (CO2) and hydrogen sulfide (H2S) and alleviate public concern resulting from 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 and shape, and leakage potential. Herein, we reviewed existing experimental data and theoretical models used to gain a better understanding of how the H2S 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 acid gas with different H2S mole fractions are of both temperature and pressure dependence, which vary among the gas, liquid and supercritical phases. Water/acid gas interfacial tension decreases strongly with increasing H2S content. For mica and clean quartz, water contact angle increases with increasing H2S mole fraction. In particular, wettability reversal of mica to a H2S-wet behavior occurs in the presence of dense H2S. 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, existing data sets do not show a consistent link between capillary number and relative permeability. The capillary pressure decreased with increasing H2S mole fraction. However, there is no consensus on the effect of the H2S content on relative permeability curves. This may be due to the limited availability of relative permeability and capillary pressure data for acid gas/brine/rock systems; thus, more experimental measurements are required.