Mechanical Modeling and Analysis of Stability Deterioration of Production Well During Marine Hydrate Depressurization Production

Different from oil and gas production, hydrate reservoirs are shallow and unconsolidated, whose mechanical properties deteriorate with hydrate decomposition. Therefore, the formations will undergo significant subsidence during depressurization, which will destroy the original force state of the production well. However, existing research on the stability of oil and gas production wells assumes the formation to be stable, and lacks consideration of the force exerted on the hydrate production well by formation subsidence caused by hydrate decomposition during production. To fill this gap, this paper proposes an analytical method for the dynamic evolution of the stability of hydrate production well considering the effects of hydrate decomposition. Based on the mechanical model of the production well, the basis for stability analysis has been proposed. A multi-field coupling model of the force state of the production well considering the effect of hydrate decomposition and formation subsidence is established, and a solver is developed. The analytical approach is verified by its good agreement with the results from the numerical method. A case study found that the decomposition of hydrate will increase the pulling-down force and reduce the supporting force, which is the main reason for the stability deterioration. The higher the initial hydrate saturation, the larger the reservoir thickness, and the lower the production pressure, the worse the stability or even instability. This work can provide a theoretical reference for the stability maintaining of the production well.