Numerical investigation of electrical heating production performance for the three-phase-coexistence hydrate deposits in South China Sea

By arranging horizontal well into the three-phase-coexistence layer of natural gas hydrates (NGHs), free gas and water, the gas production of the second NGHs production test in the South China Sea has been significantly improved. But the gas production rate is still far from meeting commercial exploitation standards. To further improve the exploitation efficiency of NGHs, several novel stimulation strategies have been proposed, including electrical heating, hydraulic fracturing, brine flooding and artificial impermeability barriers. However, the effectiveness of these strategies for the unique three-phase-coexistence NGHs deposits remains unclear. Thus, we established stable three-phase-coexistence hydrate model and conducted the numerical simulations of electrical heating assisted depressurization with/without brine flooding, impermeability barriers and hydraulic fracturing. The well configuration of dual horizontal wells arranged in the three-phase layer were utilized. The results prove that electrical heating assisted depressurization can greatly accelerate hydrate dissociation and gas production, whose cumulative gas production is 1.75 times as much as those of only depressurization. To optimize exploitation parameters, the sensitivity analyses indicate that setting horizontal wells at the top of three-phase layer and greater heating power, depressurization amplitude and well spacing produces more methane. Furthermore, brine flooding significantly reduces gas production, impermeability barriers can increase methane recovery. On the basis of optimal parameters, combining hydraulic fracturing with electrical heating achieves the optimal economic potential, whose cumulative gas production is 3.0 times as much as those of only depressurization. We hope the new insights in this study can contribute to the future commercial development of analogous NGHs deposits.