Numerical analysis of coupled thermal-hydro-chemo-mechanical (THCM) behavior to joint production of marine gas hydrate and shallow gas

Low gas production efficiency and high cost significantly impede the commercial viability of exploiting marine gas hydrate. To address this, we propose joint production of hydrate and shallow gas, focusing on previously unexplored characteristics such as fluid seepage and local deformation arising from interlayer interface. In this study, we investigate the coupled multiphysics response during depressurization in joint production. Our findings reveal that the joint production enables gas production rates to surpass commercialization threshold, with the minimum proportion of free gas in total production exceeding 0.5 during depressurization stage. Free gas stored in the reservoir promotes the energy recovery, which is correlated with permeability. We observe the water block effect, a type of interlayer interference, leading to local gas accumulation in three phase layer and heterogeneous gas effective permeability change within reservoir. Regarding geomechanical behavior, the maximum displacement occurs in the free gas layer during the 100-day test. Simultaneous compaction occurs in the upper part of the wellbore, whereas dilation is observed in the lower part. This study offers crucial insights into the characteristics and challenges of hydrate and shallow gas joint production related to interlayer interference.