Numerical Simulation of Production Dynamics in Developing Gas Hydrate Reservoirs Using a Fractured Vertical Well

Summary Hydraulic fracturing is an essential technology for improving reservoir permeability and enhancing gas well productivity. The experiments have confirmed that it is feasible to operate hydraulic fracturing in gas hydrate reservoirs. Consequently, clarifying the impact of hydraulic fracture on gas well productivity has been a crucial issue in developing a gas hydrate reservoir. This study established a numerical simulation model based on the embedded discrete fracture model (EDFM) for developing the gas hydrate reservoir using a fractured vertical well. To verify the accuracy of the newly-developed numerical simulation model, the local grid refinement method is used to simulate the hydraulic fracture with an arbitrary angle and the comparison results show that the numerical solution in this work is consistent with the solution from the commercial software. Subsequently, we evaluate the influence of the distance between the vertical well and fracture, hydrate saturation, well asymmetry factor, and natural fractures on the distributions of gas flow rate between matrix and fracture, field maps, and gas well productivity. The simulation results show that hydraulic fracturing can increase the initial daily gas production rate by 13.4 times which is favorable for enhancing gas recovery in gas hydrate reservoirs. The gas flow rate between the matrix and hydraulic fracture which can be significantly influenced by the well asymmetry factor (Ix) shows a U-shaped distribution for the scenarios of Ix = 0. Notably, thermal convection can exert a more significant influence on the temperature distribution inside the hydraulic fracture and a huge decrease in temperature caused by thermal convection will inhibit the decomposition of hydrate. In addition, natural fractures connected with the hydraulic fracture can arouse a more important impact on distributions of field maps and gas well productivity in a gas hydrate reservoir than unconnected natural fractures. The maximum gas flow rate occurs at the intersection of the natural and hydraulic fractures. As the angle between natural and hydraulic fractures (θf) is increased from 0° to 45°, a value of 24.93% increase in the cumulative gas production indicates that a higher value of θf is more favorable for developing gas hydrate reservoirs. This work provides a comprehensive understanding of developing gas hydrate reservoirs using a fractured vertical well in the future.