南海北部神狐海域天然气水合物热激发开采潜力的数值模拟分析

Numerical simulation on production potential of hydrate deposits by thermal stimulation

天然气水合物作为一种新型替代能源,如何有效开发成为当前研究的热点,热激发被认为是除降压法外天然气水合物开采的另一重要途径。目前对于天然气水合物注热开采效率和经济可行性仍没有清楚的认识。构建了通过垂直单井对天然气水合物进行注热开采的物理模型,通过对物理模型的理想简化,在水合物藏中划分出一个理想薄层,对研究的储层体系进行了密集的网格划分,并以南海北部陆坡神狐海域天然气水合物成藏特征为依据,利用TOUGH+HYDRATE程序,数值模拟研究了对天然气水合物藏进行热激发开采的潜力,并与相同幅度的降压开发进行了效率对比分析。研究显示,井孔高温热源的辐射半径很小,水合物受热分解速率缓慢,而且在注热和降压联合开采中,注热作业对水合物分解的贡献很低,水合物分解主要由降压操作引起。

Natural gas hydrate is a new potential energy, so how the gas can be effectively produced from hydrate deposits becomes a hot research topic. Heat stimulation is regarded as another important way for producing hydrate besides depressurization. However, production efficiency and economic feasibility of gas production by heat stimulation are not well understood. In this paper, a physical model for predicting gas production from hydrate deposits by heat stimulation through a vertical well is constructed. The model defines a laminar hydrate system of unit thickness. The reservoir system is discretized densely. We numerically simulate the production potential of hydrate deposit through thermal stimulation by employing the TOUGH＋HYDRATE simulator with the characteristic parameters of Shenhu hydrate on the northern continental slope of the South China Sea. Then, we compare and analyze the efficiency of heat stimulations with a pure depressurization operation. Our research shows that the radioactive radius of the high-temperature heat source at the well is very small and that the hydrate dissociation rate is slow. The contribution of thermal injection operation is very small in the inter-productions of heat stimulation and depressurization, and the hydrate dissociation in the processes are mainly aroused by the operation of depressurization.