Role of hydrodynamism in compositional heterogeneities in acid gas reservoir

Abstract : Acid gases (H2S and CO2) compositional heterogeneities have been noticed in many sour gas reservoirs. Their occurrence is an important factor of economic depreciation. Thus, the knowledge of the acid gases distribution is a critical parameter for the design of field development. The mechanisms to explain compositional heterogeneities of acid gas in a reservoir are various. The paper aims at exploring the role of an active aquifer in contact with an initial high H2S content reservoir. The major mechanisms may be controlled by: * Differential solubility of gases which can change the relative amounts of each gas near the contact; * Active aquifer solubilization and transport which can export dissolved gases thus enhancing dissolution on the long-term; * Diffusional transport in the gas phase which can transfer the compositional anomalies farther from the gas-water contact. To test the influence of several parameters on the efficiency of the acid gases leaching, simulations on basic geometries have been performed with the diphasic transport and geochemical software Hytec. The simulation results show a major role of the occurrence of horizontal impermeable barriers yields to sharp heterogeneities, including a decrease in acid gas near the contact, while farther areas H2S concentration remain unaffected.