Optimizing hydrate extraction: Balancing stability and production efficiency

Assessing the stability of hydrate deposits is essential for gas hydrate exploitation. The dual effects of hydrate decomposition and pore pressure reduction will cause stress concentration in the reservoir around the production well. In order to characterize the response of hydrate sediment deformation to effective stress and settlement displacement and evaluate its production potential, a depressurization decomposition reservoir stability model considering ’ phase change-seepage-heat transfer ’ of natural gas hydrate is established in this paper. Based on the geological data of Qiongdongnan sea area in South China Sea , the influence of production system on silty mudstone sedimentary layer in the process of depressurization mining is simulated. According to the results of effective stress and settlement displacement of hydrate reservoir caused by development location, depressurization amplitude and depressurization rate, a depressurization mining scheme of hydrate reservoir limited by reservoir deformation displacement is proposed. The study reveals the deformation and settlement mode of hydrate reservoir. The hydrate reservoir slips and settles in the upper strata, and the lower strata are compacted. The maximum strain (0.6 %) appears at the bottom hole boundary, and its location is concentrated in the near well area and the lower decomposition area of the reservoir. The study also found that when the hydrate reservoir has no large-scale settlement in the reservoir, the depressurization development scheme of short-period high-speed decline at the bottom of the hydrate reservoir can greatly improve the gas production potential of the reservoir. The balance between hydrate sediment stability and production proposed in this study can contribute to the safe, stable and efficient exploitation of marine natural gas hydrates.