Transient Pressure Well Test Analysis Based on Compressible Discrete Fracture Network

Recent years the fractured reservoir characterization is of special interest since the dual medium simulation has wide application in field studies. In practice the main difficulties that impede the simulation are evaluation of fracture properties and including of their continuous analog into reservoir model. The research focuses on characterization of deformable fractured reservoir. A new approach to evaluate fracture properties from well test has been developed. Theoretical basis of the approach is compressible discrete fracture network (CDFN) model which is an extension of the DFN concept to take into account compressibility of fractures in terms of both porosity and permeability. The fracture compressibility is related to matrix (rock) compressibility that generates change in matrix block size and fracture aperture during pressure evolution. The new approach consists of two components. The first is numerical analysis of pressure drawdown and build-up to discover behaviour that is appropriate to the compressible fracture network. The second is well test interpretation to characterize fracture density; aperture, permeability, porosity and their dependence on pressure. The interpretation consists in solution of an inverse problem using analytical procedures and can be applied to identify properties of purely fractured and fractured porous reservoirs. Simultaneously the numerical simulation of flow in CDFN is considered. The simulation of fluid flow in near well bore area allows to calibrate properties of CDFN. The approach has been tested per analysis of an actual transient pressure well test. The flow simulation allowed to compare actual and synthetic transient pressure response and hence to estimate correctness and accuracy of the approach. The developed model, approach and flow simulation allow to identify fracture properties and to calibrate them using well test simulation. Obtained fracture permeability and porosity, their dependence on pressure and matrix block size are used in dual (single) medium reservoir simulation.