Incorporation of deformation band fault damage zones in reservoir models

Dongfang Qu,Jan Tveranger

doi:10.1306/12111514166

Abstract

Fault damage zones in porous sandstones commonly exhibit networks of deformation bands reflecting crushing and reorganization of grains associated with small-scale, localized displacement. Deformation bands introduce anisotropic, order-of-magnitude reduction of effective permeability, which will affect fluid flow in reservoir rocks. We here present a method for incorporating these features in industrial-type reservoir models. The method involves the use of a three-dimensional fault zone grid generation technique that allows property modeling on a discrete high-resolution fault zone grid without refining the entire reservoir model. Deformation band data from 106 outcrop scan lines of fault damage zones were classified into discrete fault facies defined according to deformation band density. The distributional pattern of fault facies in the data exhibits recurrent spatial relationships, which could be reproduced using truncated Gaussian simulation in the modeling process. The frequency distribution of deformation band density for each facies was analyzed, and average density values were assigned to each facies for calculating cell permeability. Permeability anisotropy was handled by approximating the relationship between deformation band densities in different directions based on published high-resolution fault zone maps and cross sections. Fluid-flow simulations were carried out on several damage zones models, and results were benchmarked against models with conventional fault rendering without damage zones. Simulation results show that flow paths, remaining oil distribution, and reservoir responses in models incorporating damage zones deviate from models employing conventional fault representation without damage zones, and these differences increase as deformation band permeability decreases.

Highlights

Fault zones are generally recognized as being composed of a central fault core of varying thickness surrounded by a volume of deformed host rock or damage zone (Caine et al, 1996; Wibberley et al, 2008; Braathen et al, 2009)
The results from the analysis described above were used as input to populate the fault damage zone region with fault facies
Our study demonstrates that detailed representation of fault damage zone properties in reservoir models may both improve forecasting of reservoir behavior and aid production optimization

Summary

Introduction

Fault zones are generally recognized as being composed of a central fault core of varying thickness surrounded by a volume of deformed host rock or damage zone (Caine et al, 1996; Wibberley et al, 2008; Braathen et al, 2009). Deformation bands can induce order-of-magnitude effective permeability reductions and anisotropies (Antonellini and Aydin, 1994; Matthai et al, 1998; Taylor and Pollard, 2000; Sternlof et al, 2004; Fossen and Bale, 2007; Rotevatn et al, 2009). The effect of deformation bands on reservoir fluid flow has been addressed by some previous studies using reservoir simulation tools (Rotevatn et al, 2009; Fachri et al, 2013a) Their results suggest that the presence of deformation bands with a permeability reduction of three orders of magnitude or more relative to the host rock increases flow tortuosity and enhances sweep efficiency, which in turn delays water breakthrough and increases oil recovery. These features should be included in models employed for hydrocarbon production planning

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Discussion

Conclusion