High-Resolution Hydraulic Fracture Network Modeling on Adaptive PEBI Grids

Summary Hydraulic fracturing is currently the main technology for the development of low permeability reservoirs. As most of them are naturally fractured, hydraulic fracturing operations result in of a system of cracks, known as stimulated reservoir volume (SRV). To increase the efficiency of low permeability reservoirs development, an efficient modeling tool that allows for accurate representation of the flow in the system of intersecting fractures is needed. There is a number of low-efficiency methods in reservoir simulators for SRV modeling on structured grids. One of them is to represent fracture system using an effective continuum. Application of the Oda algorithm for computing effective permeability allows for correct representation of the flow only in combination with multipoint flux approximation. Dual porosity/permeability model is not applicable for hydraulic fractures because of the high anisotropy associated with them. In contrast, DFM-model provides a higher resolution level of the fluid flow but is computationally more expensive, and hence not widely used. For this problem a good solution is the embedded discrete fracture model (EDFM) which is based on combining two conductive media – pore space and fracture network. As EDFM is mostly used with structured grids, it is usually accompanied by algorithms of local grid refinement for better resolution in fractured regions. In this paper, we present efficient computational algorithms to calculate flows in reservoir with intersecting fractures on the unstructured PEBI grid with automatic honor of geometric features of fractured system. The computational algorithm is based on the EDFM approach tailored for PEBI grids. The proposed approach is applied to the three-phase isothermal flow problem with phase transitions, gravity and capillary forces (Black Oil). Special attention is paid to comparison of the flow modeling results on the unstructured PEBI grid using the Oda method for computing effective permeability and the proposed EDFM approach. We demonstrate efficiency of using the unstructured grid for resolving SRV fractures compared with structured grids. Calculation results are given for real fields showing the efficiency of the presented approach for flow simulation of fractured reservoir with hydraulic fracturing treatment.