Modeling Finite-Fracture Networks in a Partially Fractured Reservoir in the Middle East

Abstract

Summary Dual-porosity/dual-permeability simulation formulae are derived from reservoirs with an infinite network of fully interconnected conductive fractures. One aspect of fractured reservoirs is that not all have fully interconnected fracture networks. Most of the fractured reservoirs are only partially fractured. Partially fractured reservoirs, in contrast, consist of discrete bundles of conductive fractures and/or isolated fractures. The discrete-fracture bundles are interconnected within but are isolated from other bundles nearby. In case of partially fractured reservoirs, location, size, and shape of discrete-fracture bundles must be determined to populate the fracture grid of the dual-porosity or dual-porosity/dual-permeability simulation model. The purpose of this paper is to demonstrate how the location, size, and shape of interconnected-conductive-fracture bundles can be determined by integrating borehole-image data with depletion-curve analysis. The method was devised to populate a fracture grid of a preliminary dual-porosity simulation model for a small field in the Middle East. The field produces from a partially fractured carbonate reservoir and has only a few vertical wells. Fractures in the field are dispersed or layer-bound and seem to be related to folding. Depletion-curve analysis and image logs yield location, size, and shape of discrete-fracture bundles. Fracture porosity, permeability, and size of matrix block bounded by fractures within each fracture bundle can be calculated by use of fracture data from borehole-image logs. A critical justification for integrating image logs with depletion-curve analysis is that it is not possible to predict finite-fracture-network (FFN) location, size, and spacing only from analytical connectivity measures or stochastic discrete-fracture-network (DFN) models.