Application of a Hybrid Dual-Porosity/Dual-Permeability Representation of Large-Scale Fractures to the Simulation of a Giant Carbonate Reservoir

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe simulation of fluid flow in fractured reservoirs is mostly based on the Warren-Root formulation in which the matrix is dissected into blocks by fractures (1) . In modern simulators, the Warren-Root formulation has been extended to account for fluid flow in the matrix as well as in the fractures (2) . These two media of contrasting transmissibility and storage capacity constitute the basis of dual porosity dual permeability modeling. Hydraulic connection between the two media is managed via a transfer function. This formulation is appropriate for cases with diffuse interconnected fractures. Alternatively, fractures can be modeled explicitly by capturing their geometries, shapes and sizes in the form of numerical grid cells. But this would be prohibitively costly in terms of run time and memory. This paper presents a method that is suitable for giant fields that are dominated by clusters of sub-vertical fractures called fracture corridors. It is based on a hybrid approach of the two alternatives mentioned. The effective Warren-Root and fracture parameters are adjusted to mimic explicit fracture modeling thereby capturing the advantages of both. The method was applied to a giant carbonate field in Saudi Arabia, which has both fracture corridors and super-permeable bodies. These bodies are typically horizontal and they interconnect with the fracture corridors to form a combined high conductivity medium which is responsible for the unusual water movement observed in some parts of the field. The full field simulation model contains a homogeneous matrix and a fracture grid comprised of fracture corridors and super-permeable bodies. Fluid segregation is assumed in the fracture system in agreement with the physics inside conductive vertical fractures. The matrix-fracture corridor and the matrix-super permeable body exchanges are represented in a manner similar to matrix-fracture transfers in the Warren-Root dual-porosity system. Special attention was paid to matrix block size and to imbibition capillary pressure. This approach led to a reliable history match that captures the water arrival time and water production profiles in the reservoir.

High Permeability Streak Identification and Modelling Approach for Carbonate Reef Reservoir

“…A number of methods describe the separation of rock types in the reservoir volume and set separate dependencies for each rock type [15]. Another classical method for creating a fractured reservoir model is dual media modelling, which reflects both the matrix and the fractured components of the rock [16][17][18].…”