Hydrate reservoir deformation under multi-well strategies based on the dynamic elastic modulus relationship

In order to demonstrate the safety of the multi-well mining method, stratum deformation using multi-well systems is discussed. Firstly, ultrasonic experiments and triaxial tests of hydrate-bearing sediments under different confining pressure and hydrate saturation conditions were carried out. The soil static elastic modulus was compared with the dynamic elastic modulus relationship. Then the dynamic elastic modulus relations were applied to the multi-field coupling model to simulate the hydrate mining process in reservoirs by multi-well strategies. The experimental results show that hydrate saturation impacts the elastic modulus more than the effective confining pressure. In the simulation results, with the increase of the reservoir depth, the soil settlement shows a trend from small to large and then to small. The maximum soil displacement is located at the junction between the hydrate and the overlying layers, regarded as the weak point. In addition, increasing the well branches, expanding the well spacing, and increasing the wellhead radius can increase gas production. However, at the same time, it will also increase the reservoir deformation, thus posing risks to the stability of the formation and extraction wells. On this basis, the efficiency-safety factor was set, and the best mining scheme was determined.