Characterization of fractured reservoirs using a consistent stiffness-permeability model: focus on the effects of fracture aperture

Abstract

The successful exploitation of many hydrocarbon reservoirs may depend on proper characterization of fractured or composite porous media. However, due to anisotropy and heterogeneity, the characterization of such kind of reservoirs is a complicated task which needs proper attention and care. There are often strong correlations between the effective permeability and seismic anisotropy of fractured reservoirs. The exploitation of such correlations is extremely important in understanding of the spatial variation of anisotropic permeability. The purpose of this thesis work was to develop novel workflows and methodologies in order to exploit the correlations between effective permeability and seismic anisotropy of fractured reservoirs.The correlations between the effective mechanical and transport properties of fractured reservoirs within the context of a joint inversion of seismic and production data have been exploited to obtain improved hydrocarbon reservoir characterization.In this work, the effective mechanical and transport properties of fractured reservoirs and related systems are estimated using an efficient and consistent permeabilitystiffness model from the same parameters of microstructure. The estimated effective mechanical properties in combination with anisotropic Gassmann relations have been used to calculate the seismic amplitude versus angle and azimuth AVAZ) data i.e. reflection coefficients as a function of incidence angle and azimuth from the top of the reservoir. Similarly from the estimated effective hydraulic properties, the reservoir simulator can calculate the production data such as well bottom hole pressure, well oil production, well water cut, saturation and pressure for all grid blocks at specific time steps.The seismic AVAZ and/or production data is used in the Bayesian inversion scheme to estimate the parameters of factures (e.g. fracture density, fracture aperture and fracture orientation) required to predict permeability. This work shows that joint inversion of seismic and production data give the best results due to the less sensitivity of seismic AVAZ data to fracture aperture which is one of the most II important parameter of the microstructure predicting the permeability. This workflow of joint inversion of seismic and production data has also been applied for the characterization of faulted reservoirs (e.g., fault damage zone with deformation bands oriented parallel to the fault core). The transmissibility multiplier is used to model the effect of the fault core and the consistent rock physics model has been used to model fractures and deformation bands in the damaged zone.Analogies between different physical phenomena and coupled processes such as wave-induced fluid flow have been given a special attention to infer more useful information about fractured reservoirs containing single or multiple sets of fractures. The results obtained form these workflows and methods can help in better management of fractured reservoirs and optimum field development. IV Preface

Anisotropic permeability in fractured reservoirs from frequency‐dependent seismic Amplitude Versus Angle and Azimuth data

“…Here, Γ (0) is the background or matrix permeability, I 2 is the (Kronecker‐delta) identity for second‐rank tensors, is the volume concentration for fractures of type r and is a tensor given by the strain Green's function integrated over an ellipsoid determining the symmetry of the correlation function for the spatial distribution of fractures (see Jakobsen ; Shahraini, Ali and Jakobsen ). The for a single fracture of type r is given by (Jakobsen ): …”

“…Here, is a second‐rank tensor given by the pressure gradient Green's function integrated over a characteristic spheroid having the same shape as inclusions of type r (see Jakobsen , Shahraini et al . ) and is a second‐rank tensor of permeability coefficients for fractures of type r , which can be estimated using cubic law (Van Golf‐Racht ): where is the fracture aperture for the fractures of type r . The fracture aperture or opening is represented by the distance between the fracture walls.…”

History matching of dual continuum reservoirs—preserving consistency with the fracture model

“…Couplings of this type has been suggested, e.g., by Jakobsen et al [8] and Sharani et al [22]. In these applications, fracture parameters are the natural choice of inversion variables, since all the relevant physical properties can be calculated from them.…”

Fundamental controls on fluid flow in carbonates: current workflows to emerging technologies

“…Although by no means mature, improved approaches to predict anisotropic permeability have been explored through the analysis of frequencydependent seismic amplitude v. angle and azimuth data (Ali & Jakobsen 2013). Constraints on fracture apertures have been sought through joint seismic inversion combined with analysis of production data (Shahraini et al 2011). Further efforts include those that provide links to geomechanics and production data (Kozlov et al 2007), as well as structural analysis and fracture modelling (Liu et al 2007a).…”