Numerical analysis of the geomechanical responses during natural gas hydrate production by multilateral wells

Abstract

Multilateral wells are acknowledged as a promising well type to achieve the commercial development of natural gas hydrate. Previous studies have validated the efficacy of multilateral wells for hydrate mining without considering the geomechanical responses. However, effective stress increases during hydrate extraction by depressurization, and the reservoir skeleton degrades with hydrate dissociation, which might induce stress concentration, stratum subsidence, seafloor inclination, and other hazards. Understanding the geomechanical responses is thus crucial for the design of hydrate exploitation utilizing multilateral wells. As a continuation of our previous study, a coupled thermal-hydrologic-mechanical model was constructed to investigate the geomechanical responses during hydrate production by multilateral wells. Results reveal that multilateral wells can upgrade geomechanical risks and gas production capacity for hydrate exploitation. Stress concentration and stratum sinks are prevalent around the multilateral well. Increasing production pressure may alleviate stratum subsidence but has a noticeable impact on gas production. Since stratum inclination generated by hydrate mining with multilateral wells is minimal, geological catastrophes are most improbable. For utilizing multilateral wells in hydrate extraction, it is recommended to pay more attention to wellbore and wellhead safety.