Analyzing the applicability of in situ heating methods in the gas production from natural gas hydrate-bearing sediment with field scale numerical study

摘要

For natural gas hydrate (NGH) exploitation, the in-situ electrical heating has been proved as a promising production method in laboratory experimental scale. But the results in this scale are difficult to reliably reflect field trials due to limitations in the size of the reactor. So, by TOUGH HYDRATE software, this paper stimulates hydrate exploitation in field scale by in situ electrical heating. In addition, depressurization is applied as a comparison. Based on the analysis of several parameters like reservoir temperature and hydrate distribution, results show that although a larger heating power can result in a faster move of the decomposition front, the fast free gas production takes a large amount of sensible heat out of the reservoir. Also, the electrical heating effect is limited by the heat conductivity of formation in the field scale, so the heat promoting distance of the heating method is less than 10 m after five years production even with 1000 W/m of electrical heating power. A large amount of heat loss and the shortage of heating injection make the energy efficiency of it decreased significantly with the production time. So, large heating power cannot always remain fast gas and water production rates. Furthermore, the higher heating power does not mean a better exploitation effect. Thus, it is vital to choose a reasonable heating power in the field exploitation. Under the NGH reservoir and production parameters set in this paper, the most optimal electrical heating power should be 500 W/m with comprehensive consideration of gas production rate, NGH front promoting velocity and energy efficiency.