A NEW METHOD TO CALCULATE EFFECTIVE PERMEABILITY OF GRIDBLOCKS USED IN THE SIMULATION OF NATURALLY FRACTURED RESERVOIRS

Current simulation technology for naturally fractured reservoirs is ba sed on either the continuum or the discrete-fracture approach. The mor e commonly used continuum model can simulate complex recovery mechanis ms. However, it uses a very simplified representation of the fracture system for calculating effective fracture permeability. The discrete-f racture flow method can handle complex fracture geometry. However, its use has been typically limited to basic flow calculations through a c onnected fracture system embedded in zero-matrix-permeability rock. We have developed a new technique for estimating the effective permeabil ity of gridblocks used in conventional simulators. The idea behind thi s technique is to integrate the realism of fracture systems, as captur ed by discrete-fracture models, with the complexity of the now calcula tions offered by continuum models. The end product of developing this technique is an efficient numerical code based on the boundary-element method. This code permits the fracture system to be complex and poorl y connected, and it also includes the contribution from flow through t he matrix rock. For fluid flow in the matrix rock, the fractures are t reated as planar-source distributions. Periodic boundary conditions, f or the flow properties, are used for the calculation of the effective permeability of individual gridblocks. We first use a simple fracture system to demonstrate the validity of our method and to evaluate the s ensitivity of the results to matrix and fracture properties. We then u se fracture statistics data from the Mesaverde sandstone, effective pe rmeability Values from our code, and a continuum simulator to calculat e tracer-flow patterns for a more realistic system.