Hybrid embedded discrete fracture model for complex fractures, faults, and irregular boundaries on unstructured grids

This study presents a novel hybrid numerical model designed to handle complex geological settings characterized by multiple faults, intricate fracture networks, and irregular domain boundaries, common features in many aquifer systems. Building upon the discrete fracture model concept, unstructured grids conforming to faults and boundaries are generated, ensuring precise representation of these large-scale geological structures and their coupling with the surrounding porous matrix. Smaller-scale natural and induced fractures are then efficiently incorporated using an embedded discrete fracture model, calculating non-neighboring connections within the unstructured grid framework. Finally, numerical simulations are performed using the finite volume method. This model ensures an accurate portrayal of boundaries and faults, as well as efficient computation with a suitable number of grids. The accuracy of the proposed model is validated against 2 benchmarks, employing the standard discrete fracture model as a reference: a two dimensional (2D) parallel-fracture and a three dimensional (3D) orthogonal-fracture. The applicability of the model is further demonstrated through a complex benchmark example involving 400 randomly distributed fractures and a single undulating fault, highlighting the influence of fault presence on production behavior. Overall, this work offers a robust numerical framework for improving the predictive capabilities of subsurface flow models in complex geological environments critical to water resources.