A Potential Commercialization Method for Gas Production from Off-Shore Hydrate Reservoirs

Depressurization and heat injection are viewed as the main methods to be used in natural gas hydrate (NGH) exploitation. However, these methods have limitations, such as low energy-utilization efficiency or a limited extraction range, and are still far from commercial exploitation. In this work, we propose a potential commercial method to exploit NGHs by effectively using geothermal energy inside deep reservoirs. Specifically, a loop well structure is designed to economically extract geothermal energy. Based on an analysis of our developed model, when the looping well is coupled with depressurization, the profits of high NGH production can surpass the drilling costs of extracting geothermal energy. Moreover, as the temperature of fluids from the geothermal layer exceeds 62 °C, the fluid heat is mainly consumed by the rock matrix of the hydrate formation, instead of promoting NGH dissociation. Based on this threshold temperature, a loop well drilled to a depth of about 4000 m for hydrate sediment in the Shenhu area of the South China Sea would be able to efficiently extract geothermal energy, leading to an approximate 73% increase in gas production in comparison with conventional depressurization. An economic analysis suggests that our proposed method can reduce the exploitation cost of methane to 0.46 USD·m −3 . Furthermore, as the hydrate saturation increases to 0.5, the exploitation cost can be further reduced to 0.14 USD·m −3 . Overall, a looping well coupled with geothermal energy and depressurization is expected to pave the way for commercial NGH exploitation.