Numerical simulation of depressurization production of natural gas hydrate in different well types

Natural gas hydrate is a widely distributed and abundant clean energy. Due to the great difficulty of its exploitation, natural gas hydrate has not formed a commercial exploitation scale at present, and it mainly stays in the stage of theoretical research and trial exploitation. Therefore, studying the gas production characteristics of hydrate and analyzing the recovery effect under different depressurization mining modes is important for large-scale commercial exploitation in the future. A mathematical model is brought up in this paper based on the open-source simulation program of TOUGH + HYDRATE, considering the four phases of gas, water, hydrate and ice. Based on the geological data of the first trial production of natural gas hydrate in Shenhu area of the South China Sea, this paper establishes the geological model of natural gas hydrate containing underlying free gas and carries out the numerical simulation of depressurization production. The production characteristics of hydrate decomposed gas and free gas in the production process are analyzed, and the recovery rates of hydrate and free gas under different completion methods and fracturing conditions are compared and analyzed. This study shows that the production of natural gas hydrate is highly dependent on the development configuration including well placement and stimulation.