Optimization of the natural gas hydrate hot water injection production method: Insights from numerical and phase equilibrium analysis

The heat injection during depressurization is a crucial technique for sustaining the long-term gas production rate of natural gas hydrate. To analyze the production patterns and mechanisms of hydrate dissociation under various heat injection conditions and to further optimize heat injection strategies, this study establishes a reservoir-scale three-dimensional heterogeneous computational model using a self-developed hydrate simulator. A novel in-situ heating method utilizing bottom seawater is proposed for heat injection, and comprehensive analyses of heating power and injection rates are conducted. The results indicate that increasing heating power at a constant injection rate enhances gas production rates while reducing thermal efficiency. Simultaneously, under constant heating power, gas production rates initially increase and then decrease with increasing injection rates, revealing the presence of an optimal injection rate. This paper introduces the concepts of temperature driving force and temperature modification ratio, analyzes the mechanisms of heat injection development, and derives an optimized strategy for hot water injection through curve fitting. This research enhances our understanding of the integrated approach involving thermal stimulation and depressurization, providing significant guidance for future production endeavors.