The Layout Optimization of the Dual-Horizontal Depressurization Wells for Gas Hydrate Exploitation Considering the Interwell Interferences

Abstract

Gas hydrate is viewed as a potential energy, and the multihorizontal depressurization wells are expected to achieve its commercial production. However, how to optimize the multihorizontal wells layout in hydrate reservoirs is controversial. In this research, the numerical study on the hydrate exploitation from the Shenhu Area of the South China Sea by the dual-horizontal depressurization wells (DHDW) was conducted, and the optimal spatial position of DHDW was first studied. It is realized that the optimal spatial position of DHDW for gas hydrate production should be in the center of the hydrate layer. Based on this conclusion, the influences of the well spacing between DHDW (ranging from 22 to 582 m) on hydrate exploitation were then investigated. It is found that there was a strong interference between DHDW when the well spacing was smaller, leading to the lower total produced gas volume. When the well spacing increased to a certain value, the interference disappeared, and the total produced gas volume reached the maximum. On this basis, a new method to calculate the optimal well spacing (d_o) between DHDW was proposed. According to the calculation, when the exploitation period was 10 years, the d_o between the DHDW values was 73.06 m. Finally, the influences of the permeability (k) in the hydrate layer (2.9–145 mD) and the exploitation period (t) of gas hydrate (5–30 years) on the d_o were further studied. The function relations of d_o and k, and d_o and t were obtained, respectively. Furthermore, the implications for the optimal layout of multihorizontal depressurization wells in hydrate reservoirs were discussed. This study could provide guidance for the efficient exploitation of gas hydrate.