A New Method To Calculate Effective Permeability of Gridblocks Used in the Simulation of Naturally Fractured Reservoirs

Abstract

Current simulation technology for naturally fractured reservoirs is based on either the continuum or the discrete-fracture approach. The more commonly used continuum model can simulate complex recovery mechanisms. However, it uses a very simplified representation of the fracture system for calculating effective fracture permeability. The discrete-fracture flow method can handle complex fracture geometry. However, its use has been typically limited to basic flow calculations through a connected fracture system embedded in zero-matrix-permeability rock.We have developed a new technique for estimating the effective permeability of gridblocks used in conventional simulators. The idea behind this technique is to integrate the realism of fracture systems, as captured by discrete-fracture models, with the complexity of the flow calculations 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 poorly connected, and it also includes the contribution from flow through the matrix rock. For fluid flow in the matrix rock, the fractures are treated as planar-source distributions. Periodic boundary conditions, for 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 sensitivity of the results to matrix and fracture properties. We then use fracture statistics data from the Mesaverde sandstone, effective permeability values from our code, and a continuum simulator to calculate tracer-flow patterns for a more realistic system.

Development of an Efficient Embedded Discrete Fracture Model for 3D Compositional Reservoir Simulation in Fractured Reservoirs

“…In order to homogenize small-scale fractures, Oda (1985) derived a simple analytical expression for enhanced matrix permeability for gridblocks that contain very short fractures. Likewise, Lough et al (1997Lough et al ( , 1998 developed a boundary element method (with uniform pressure and periodic boundary conditions) to calculate effective conductivity for gridblocks containing multiple fractures.…”

Joint Inversion of Fracture Model Properties for CO2Storage Monitoring or Oil Recovery History Matching

“…The reservoir engineer may choose between three models: -a single-medium porosity model, where the fractured reservoir is represented by an equivalent porous medium. There are one porosity value and one permeability value per grid cell [22]; -a dual-porosity single-permeability model where two porous media are defined. An exchange flux is introduced to model the communication between the fractures and the matrix.…”

Integration of static and dynamic reservoir data to optimize the generation of subsurface fracture map

“…Estimation of the effective permeability tensor for regular fracture pattern of simple geometries was first proposed by Lough (Lough et al 1997). The approach was further improved by Teimoori et al (2005) to simulate fluid flow in arbitrary oriented and intersected fracture system (Teimoori et al 2005).…”