The Role of Ice Formation in Gas Production from Gas Hydrate-Bearing Sediments via Depressurization: A Field-Scale Numerical Investigation

Abstract

Depressurization using horizontal wells is widely recognized as the most economical and effective method for natural gas hydrate (NGH) production. However, research on ice formation during horizontal well depressurization remains limited, particularly under low-temperature hydrate-bearing layer (HBL) conditions. In this study, a field-scale numerical model considering ice formation during horizontal well depressurization in the HBL of the Lingshui 18-1 area, South China Sea, is developed using COMSOL Multiphysics. Comparative simulations are conducted for cases with and without ice formation. The results show that ice undergoes a cyclic process of formation and melting. Ice formation releases latent heat, slightly promoting hydrate dissociation, but the blockage of pores and pressure diffusion dominates, reducing the overall dissociation rate. Ice formation also suppresses water production more significantly than gas production, thus increasing the gas–water ratio and improving the energy efficiency. Compared with the TPL well system, the HBL well system achieves higher long-term gas production and gas–water ratios. In terms of well layout, the TPL well is suitable for short-term gas production, but the HBL well is better for long-term gas production. This study highlights the significance of considering ice formation in horizontal well hydrate production and demonstrates the feasibility and advantages of locating production wells in the HBL.