Numerical Simulation of Natural Gas Hydrates Production on the Alaska North Slope under Depressurization Combined with Thermal Stimulation

Abstract

The decomposition of natural gas hydrates (NGH) is a process controlled by both temperature and pressure conditions. The pressure drop leads to the dissociation of hydrates, which absorb heat during decomposition, also causing a decrease in the reservoir temperature. It is adverse to long-term natural gas production. Therefore, while reducing the pressure during hydrate exploitation, attention should be paid to replenishing the reservoir heat. Wellbore electric heating can directly supplement the heat around the production well, while avoiding the formation of secondary hydrates. In this article, the Alaska North Slope is chosen as the study field. The high porosity and permeability of the hydrate reservoir are conducive to simulating heat and mass transfer. Based on the geological data, a 3D layered heterogeneous geological model was constructed. The horizontal well was arranged in the upper part of the hydrate layer. The effects of initial depressurization, heating power, and heating well section arrangement on the natural gas production behavior were studied. At the same time, the evolution laws of the seepage parameters under different production schemes were analyzed. The results show that: (1) The wellbore heating can effectively promote NGH production. When the heating power was 10 kW, the V_P increased by 24.8%. (2) Depressurization plays a dominant role in the combined exploitation method. (3) Higher heating power causes a larger range of hydrate decomposition zone. When the heating power changed from 5 kW to 40 kW, the V_P increased by 40.3%. (4) The placement of the heating well section is related to NGH productivity. When the length of the heating well section changed from 50 m to 100 m, the V_P increased by 6.6%. When the location of the heating well section changed from 0 to 50 m to 100–150 m, the V_P increased by 6.9%. (5) The EER of production is influenced by the initial pressure drop, heating power, and layout of the heating well section.