Embedded Discrete Fracture Model for Investigating the Effect of Fractures on Gas Hydrate Production

Abstract

Fractures play key roles as a flow pathway in marine sediments, closely related to fluid migration and gas hydrate accumulation. The methane behavior in the presence of fractures was investigated by numerical simulation. However, the method of expressing fractures employed by most of the existing numerical simulators for gas hydrate systems is local grid refinement, bringing issues of the inability to handle fractures with a complex distribution and a large number of computational cells. In this study, an embedded discrete fracture model is built in a widely used Tough + Hydrate simulator to address this limitation. By this approach, several advantages can be achieved: (1) enhancing the simulator’s ability to handle complex fracture distributions by meshing sediments before dividing fractures to simplify the process of domain discretization; (2) improving computation efficiency through reducing the total number of computational cells. The model proposed is validated in the scenarios of single fracture and double intersecting fractures, and the results are found to fit well with those of the scheme of local grid refinement. Based on the above considerations, a conceptual model for clayey hydrate reservoirs with fractures, either natural or artificial, is constructed by the embedded discrete fracture model and applied to evaluate the production performance of the exploitation for such reservoirs. The results obtained suggest that hydraulic fracturing is an effective development method for such reservoirs, leading to a significant increase of approximately 300% in methane production.