Consideration of Damaged Zone in a Tight Gas Reservoir Model With a Hydraulically Fractured Well

摘要

This paper provides a detailed description of conditions in the hydraulically damaged fracture environment after closure and how to integrate them into a reservoir-simulation model. A special model-initialization algorithm was developed and realized in a support tool to make possible the computing of a post-fracture performance in tight gas formations by a reservoir simulator. The input represents the treatment schedule of the fracturing process and some results produced by commercial fracturing packages or geophysical measurements. To represent the fracture geometry and properties, the information about the distribution of the proppant concentration in the fracture as well as the fracture-width variation is translated into the permeabilities and porosities of the fracture gridblocks. To determine the fracturing-fluid saturation in the invaded zone, a new approach was derived to imitate the fracture propagation at a fracturing period under consideration of the leakoff processes. The penetration of the fracturing fluid into the matrix was modeled by the Buckley-Leverett equations for two-phase nonmiscible displacement, with boundary conditions provided by a classical leak-off theory. The approach is illustrated with a simulation model prepared for the analysis of the cleanup process in a damaged fractured well within a Rotliegende tight gas formation in north Germany.