Study on Wellbore Stability During Depressurization Exploitation of Marine Hydrates

Two depressurization test productions in the South China Sea have explored the feasibility of exploiting marine natural gas hydrate (NGH) resources. Natural gas hydrate wells are generally located in shallow seabed formations with poor diagenesis, and one of the key issues to be addressed for the next step of exploring commercial development is the long-term stability of production wells. This study focuses on the stability evolution law of marine natural gas hydrate production wells, constructs a full-scale stability analysis model for hydrate production wells, and reveals the wellbore mechanical response law under settlement and the wellbore instability mechanism under depressurization exploitation conditions. The results show that long-term depressurization exploitation can lead to wellhead settlement and horizontal deflection, and there is a risk of cement sheath damage in the latter half of the wellbore build section. The research results can provide theoretical guidance for the design and construction of marine natural gas hydrate production wells.