Three-dimensional upscaling of fault damage zones for reservoir simulation

Abstract

Major faults are surrounded by damage zones of minor faults that, in siliclastic rocks, can form barriers to flow in their own right. Reservoir flow simulation, now a routine part of reservoir management, requires equivalent hydraulic parameters on the scale of the whole fault. Geological models of structurally complex reservoirs, from which flow simulator grids are generated, require information on the 3D characteristics of fault populations. Here, 3D stochastic models of fault damage zone (FDZ) architecture are generated based on fault population statistics (offset, orientation, length, thickness, spatial distribution) measured from seismic, outcrop and core data. These FDZ models provide input to a 3D discrete fault flow model (DFFM) and we consider the case when the minor faults have permeabilities (isotropic) that are several orders of magnitude lower than the host rock, and thus form partial barriers to flow. The DFFM is used to determine and characterize the impact of the parameters defining the FDZ on the predicted bulk FDZ permeability, connectivity, 'efficiency' as a barrier or retarder to flow, and the 'effective' fault rock throw to thickness relationship for the FDZ. The latter of the summary results presented provides a means for incorporating FDZs into conventional production simulation package models of structurally complex reservoirs.

Treatment of faults in production simulation models

“…Clearly, this is an overly simplistic assumption. However, the use of such empirical relationships is partly supported by the results from numerical modelling of single-phase flow through complex fault zones (Harris et al , 2007. In particular, the numerical results suggest that an effective fault rock thickness equal to around 50% of the total fault thickness (measured in a perpendicular transect through seismic-scale faults and their associated damage zones), could be used to calculate TM values that take into account fluid flow across the main fault plane and through the associated damage zones.…”

Fault seal mapping – incorporating geometric and property uncertainty

“…In addition to the sources of uncertainty discussed and modelled in this paper, additional uncertainties arise from the effects of multiphase flow (Manzocchi et al 2002;Fisher & Jolley 2007), multiple fault strands within the fault damage zone (Harris et al 2007), and the internal juxtapositions of high/low permeability zones within the fault zone (Fredman et al 2007).…”

The challenges and impact of compartmentalization in reservoir appraisal and development

“…Møller-Pedersen & Koestler 1997;Coward et al 1998;Jones et al 1998;Nieuwland 2003;McClay 2004;Swennen et al 2004;Boult & Kaldi 2005;Shaw 2005;Sorkhabi & Tsuji 2005;, Jolley et al 2007aLonergan et al 2007;Wibberley et al 2008a). In understanding the uncertainties and risks from compartmentalization these largely lie in the areas of: reservoir scale structural analysis Dee et al 2005;Fossen & Bale 2007); fault and fracture growth, fault zone architecture and characterization Wibberley et al 2008b); fault seal prediction (Bretan et al 2003;Dee et al 2007); the incorporation of faults and fault zone properties in reservoir models and simulation (Manzocchi et al 1999(Manzocchi et al , 2002(Manzocchi et al , 2008Harris et al 2005Harris et al , 2007Childs et al 2007;Fisher & Jolley 2007;Zijlstra et al 2007); integrated fluid description (Smalley & England 1994;Larter & Aplin 1995;Smalley et al 2004); the use of geomechanical data along with field and inter-well scale stress and strain analysis and modelling -incorporating the use of micro-seismicity for surveillance (Heffer 2002;Rutledge et al 2004;Sanderson & Zhang 2004;Main et al 2007;Zhang et al 2007;Osorio et al 2008). …”

“…Application of these approaches at a scale an order of magnitude or more below seismic resolution, coupled with forward modelling of strain from restored reconstructions of 3D structural restorations, enables an understanding of subseismic fault predictions to be determined with an understanding of the related uncertainty range. With advances in non-orthogonal grid manipulation techniques and the ability to incorporate local grid refinement in reservoir engineering simulation software, we have an opportunity to integrate these geomechanical predictions with multiple sedimentological, geochemical, fault and fracture property realizations (Harris et al 2007;Jolley et al 2007b;Main et al 2007;Mäkel 2007;Zhang et al 2007;Manzocchi et al 2008). When the modelling system is linked to real-time (down hole) reservoir monitoring data, we will be able to make live updates of our models and forward prediction of primary, secondary and tertiary recovery behaviour and sweep efficiency (Reddick 2006).…”