Numerical Analysis of Soil Deformation and Collapse Due to Hydrate Decomposition

Natural gas hydrates are an ideal alternative clean energy source. Many countries are currently attempting the trial production of gas hydrates. Japan became the first country to achieve offshore hydrate trial production in 2013, and China conducted 60 days of continuous trial exploitation in 2017. This study analyzes the changes in the internal stress of the hydrate zone and hydrate saturation of the soil throughout the monitoring period and calculates the failure stress of the hydrate deposit layer. The Mohr-Coulomb model is used to simulate Japan's test exploitation conditions to verify the feasibility of the method. Finally, the hydrate decomposition range, the difference in the soil dip angle in the test exploitation area, and the bearing capacity of the hydrate reservoir are numerically simulated to evaluate the stability of the soil. Through the sensitivity analysis of the hydrate decomposition range and the inclination angle of the hydrate sediment layer, it can be found that the hydrate decomposition range has the greatest impact on the deformation, and the soil around the decomposition area may be sheared and collapsed. Within 1 week of decompression and exploitation, the hydrate decomposition radius is approximately 3 m. When the inclination angle increases from 3° to 9°, the sediment deformation increases by 12 times. Therefore, it is necessary to pay attention to the critical value of the decomposition range during the exploitation process.