A Semi-Analytical Model for Production Simulation of Complex Fracture Network in Unconventional Reservoirs

Abstract Unconventional reservoirs, such as tight oil and shale gas reservoirs have emerged as a significant source of energy supply in the world. The technologies of horizontal well drilling and hydraulic fracturing have made it possible for such reservoirs to be developed commercially. Interacting with the pre-existing natural fractures, multi-stage hydraulic fracturing along horizontal wells creates complex fracture networks. Compared with the traditional single or multiple planar fractures, the flow process in these fracture networks is significantly different due to the complex interplay of flow between the interconnected fractures. This paper presents a semi-analytical model for production simulation of complex fracture networks in which hydraulic and natural fractures can interconnect with arbitrarily angles. To model the flow behavior more rigorously, we represent fractures within the network explicitly rather than idealize them as a dual-porosity medium. In the model transient response is obtained from coupling a reservoir flow model and a fracture network flow model dynamically. Source functions in real domain and superposition principle are adopted to model the flow process in reservoir analytically; thus, the flow equation of network is solved by finite difference method numerically. Furthermore, Star-Delta transformation is introduced to solve flow redirection and flux redistribution among the interconnected fractures within network. The validation of the semi-analytical model is demonstrated in comparison to the solution of ECLIPSE simulator. Production simulation of orthogonal and un-orthogonal fracture networks are taken by use of the semi-analytical model. In addition, with a field example from the Barnett shale, we show the capacity and practical use of the model to evaluate well performance and stimulation effectiveness of complex fracture network in unconventional reservoirs.