Effect of burden layers on hydrate exploitation through the horizontal well

The mass and energy transfer between the burden layers and the hydrate layer will directly affect the gas production and reservoir mechanical response during the depressurization. At present, numerous studies have focused on the impact of the hydrate layer itself. To explore the effect of burden layers on hydrate exploitation, this paper predicts the gas production and seabed settlement using a coupled thermal-hydrological-mechanical-chemical simulator. The simulation results indicate that the hydrate decomposition edge reaches the burden layers (breakthrough), leading to a significant decrease in the gas production rate. This is primarily contributed to the fact that more fluid in the burden layers flows toward the wellbore, inhibiting the gas hydrate decomposition. The horizontal well should be located in the lower middle of the hydrate layer, which can effectively utilize the formation pressure without producing a breakthrough. However, the burden layers are subject to a pressure drop whether a breakthrough occurs or not, resulting in the burden layers' settlement. And, the burden layer settlement increases significantly with the decrease in the permeability. As a result, employing artificial impermeable barriers within burden layers to improve gas production may raise safety issues. In conclusion, this paper elucidates the mechanism of burden layers' influence on gas hydrate exploitation, which is of significance for the design and optimization of plans.