Compared to heat injection or depressurization, depressurization combined with an in situ electrical heating method offers advantages in strong decomposition driving forces and low heat transfer losses. It demonstrates promising potential for commercial exploitation of natural gas hydrates. Laboratory-scale experiments have confirmed the efficiency of this combination method, but its performance on the field scale remains unclear due to the scale effect of the reservoir. This study develops a numerical model for NGH exploitation using TOUGH + HYDRATE software and validates it against the laboratory experimental data. Subsequently, a field-scale exploitation model is constructed on the basis of the actual reservoir characteristics at the W17 site in the Shenhu area of the South China Sea. The influences of the wellbore arrangement, electrical heating power, and production pressure on NGH exploitation are systematically investigated. The results indicate that at the field scale, the permeability and the thermal conductivity of the reservoir constrain the effective propagation of the pressure difference and electrical heating. This limits the promotional effects of reducing the production pressure or increasing heating power on hydrate decomposition. The wellbore arrangement significantly affects the fluid flow and also the heat convection. Separating the locations of the production well and the heating well reduces heat losses and enhances convective heat transfer, thereby improving the exploitation efficiency. Notably, from the comparisons between the results at the laboratory scale and those of the field scale, it can be seen that the NGH exploitation effects of the former are markedly influenced by the boundary effects and the heat supply from the surrounding environment. This leads to an overestimation of the effectiveness of pressure reduction and heating power increase. Future research should focus on further optimizing the synergistic effect between heating power and production pressure, exploring the optimal timing for ceasing heating, and effectively utilizing heat transfer from the surrounding environment to achieve an efficient exploitation.
Liu et al. (Wed,) studied this question.