Geomechanical Dynamic Numerical Simulation Study on Depressurization Exploitation of Natural Gas Hydrate in Horizontal Wells

ABSTRACT: Natural gas hydrates (NGHs) primarily reside within the sediment pores of deep-sea seabeds and permafrost regions, where the original low-temperature and high-pressure conditions maintain its stability. Compared to vertical wells, horizontal wells offer a larger flow area, effectively promoting hydrate decomposition and improving depressurization efficiency. However, the stress changes induced by the exploitation process may increase the risks of sand production and formation deformation, requiring further investigation of these mechanisms. This study utilizes data from secondary field tests in the South China Sea to establish a geomechanical response model with multi-physical field coupling, systematically analyzing the effects of depressurization and hydrate dissociation on sand production and reservoir subsidence. The results show that: 1) Initial depressurization near the wellbore, combined with hydrate decomposition, markedly increases sand production risks; 2) Sand production in horizontal wells occurs across multiple zones and gradually localizes in regions of heightened stress, potentially leading to wellbore blockages over time; 3) Hydrate decomposition may lead to significant formation subsidence, particularly in the central section of the wellbore. This study provides valuable insights and references for addressing geomechanical challenges in the depressurization exploitation of NGH in horizontal wells.