A NOVEL METHOD FOR NATURAL GAS HYDRATE PRODUCTION: DE-PRESSURIZATION AND BACKFILLING WITH IN-SITU SUPPLE-MENTAL HEAT

Natural gas hydrate(NGH) is the most promising clean alternative energy resource for world, which will be the strategic breakthrough of energy revolution in the future. Because the decomposition of NGH is a complicated physical and chemical process accompanied by phase change, there are still many bottleneck problems to be resolved with respect to the safe and economic exploitation of NGH. At present, the depressurization method is relatively economic and effective, but the average daily production of natural gas is far from the demand of commercial development. Based on the analysis of the bottleneck problems in depressurization method, a novel method for natural gas hydrate production, depressurization and backfilling with in-situ supplemental heat, is proposed. Three basic principles of the method are emphatically analyzed. The technology scheme, key techniques and implementation steps of the method are introduced. The conclusions are as follows: (1)The achievement of large-scale production of NGH by depressurization depend on three key factors, namely heat supply, reservoir stability and reservoir permeability. (2)Based on the three principles of depressurization, in-situ supplemental heat and backfilling and increased permeability, the novel method was proposed. In this method, calcium oxide(CaO)powder is injected into the hydrate reservoir, which will provide a large amount of heat for the decomposition of NGH. At the same time, the Ca(OH)₂ produced by the reaction will backfill the void volume left by hydrate decomposition and improve the permeability of the reservoir. (3)This study put forward the technology scheme, key techniques and implementation steps of the novel method. The method is mainly implemented in three stages, i.e., horizontal well drilling and completion, high-pressure air powder injection and depressurization and backfilling. In the future, it is necessary to strengthen international scientific research cooperation, deepen interdisciplinary R&D of innovative technologies, and realize the large-scale production of NGH as soon as possible.