Modeling of heterogeneous reservoirs with damaged hydraulic fractures

Abstract

The significance of unconventional low-permeability reservoir development has been well recognized in recent years. Pressure- and rate-transient behavior analyses are crucial methods of finding key factors that affect well production in these formations. However, previous analytically or semi-analytically based gridless models of pressure- and rate-transient response analyses for multi-stage fractured horizontal wells (MFHWs) mainly deal with homogeneous reservoirs and merely use skin factors to describe the fracture damage. Fracture damage normally refers to the conductivity reduction within hydraulic fractures and the matrix permeability or porosity impairment near the fracture face. The widely applied skin factors are derived under steady-state conditions and are accurate only when the damage length is small. They also show inability to simulate partially propped fractures and multiple fracture damage scenarios.In this article, a general linear flow model is established to simulate heterogeneous box-shaped unconventional low-permeability reservoirs with closed outer boundaries and various hydraulic fracture damage, including (1) fracture near-wellbore damage caused by proppant flow-back, over-displacement, embedment, crush or ineffective placement, (2) partially propped fractures with undamaged near-wellbore regions, (3) fracturing fluid leak-off damage in the adjacent matrix, (4) dual or multiple damage effects under unsteady-flow conditions. The fracture interference in heterogeneous reservoirs is modeled by our previous method (Zeng et al., 2018).The basic model has been verified against well-testing software KAPPA, and satisfactory agreements are obtained. New type curves have been generated with distinct flow regimes for specific fracture damage mechanisms. Sensitivity analyses have been conducted to find out how the damage properties affect the shape and duration of these distinct regimes. Reservoir heterogeneity combined with fracture damage makes the pressure and rate behavior deviate significantly from the undamaged homogeneous one and controls the fracture flux distribution in certain regimes during production for both constant-rate and constant-pressure production cases. In addition, field data from the Cardium unconventional light oil formation in western Canada are analyzed through type curve matching, which demonstrates the benefits of our model. The findings of this model are potentially helpful for field data analyses and fracture damage diagnostic.