Faults in conventional flow simulation models: a consideration of representational assumptions and geological uncertainties

Abstract

Even when geologically based methods are used to determine fault rock permeabilities and thicknesses for input into flow simulators, a wide range of simplifying assumptions regarding fault structure and content are still present. Many of these assumptions are addressed by defining quantitative and flexible methods for realistic parameterization of fault-related uncertainties, and by defining automated methods for including these effects routinely in full-field flow simulation modelling. The fault effects considered include: the two-phase properties of fault rocks; the spatial distributions of naturally variable or uncertain single-phase fault rock properties and fault throws; and the frequencies and properties of sub-resolution fault system or fault zone complexities, including sub-seismic faults, normal drag and damage zones, paired slip surfaces and fault relay zones. Innovative two-phase or geometrical upscaling approaches implemented in a reservoir simulator preprocessor provide transmissibility solutions incorporating the effect, but represented within the geometrical framework of the full-field flow simulation model. The solutions and flexible workflows are applied and discussed within the context of a sensitivity study carried out on two faulted versions of the same full-field flow simulation model. Significant influence of some of these generally neglected fault-related assumptions and uncertainties is revealed.

A method for generating volumetric fault zone grids for pillar gridded reservoir models

“…Shape and size of the fault zone may vary according to tectonic style, displacement magnitude and mechanical properties of the host rock, but generally it can be subdivided into a fault core, accommodating the bulk of deformation, and a surrounding damage zone, both displaying structural elements such as lenses, slip surfaces, fractures and deformation bands (Braathen et al, 2009;Caine et al, 1996;Chester and Logan, 1986;Peacock et al, 2000). The inherent structural and petrophysical complexity of fault zones produces correspondingly complex flow patterns inside and across the fault zone Aydin, 1994, 1995;Caine et al, 1996;Fisher and Knipe, 2001;Fowles and Burley, 1994;Odling et al, 2004); thus faults can act both as pathways and obstacles to sub-surface fluid flow (Caine et al, 1996;Chester and Logan, 1986;Manzocchi et al, 2008Manzocchi et al, , 1999Seront et al, 1998) and considerably influence petroleum migration, accumulation and recovery.…”

“…Limitations related to modeling conventions, grid types, grid resolution and computational cost further constrain the level of detail that can be included in fieldsized simulation models. The pragmatic solution to these issues has been to simplify the way in which faults and fault properties are implemented in geo-and simulation-models (Manzocchi et al, 2010(Manzocchi et al, , 2008.…”

Sand Textural Control on Shear-Enhanced Compaction Band Development in Poorly-Lithified Sandstone

“…Several recent publications provide quantitative data on the petrophysical properties of deformation bands [6][7][8][9][10][11] and more detailed separating deformation bands into compaction bands and shear enhanced compaction bands [12,13].These properties provide valuable input for reservoir models [14][15][16] and the understanding of reservoir flow properties. Recently, structural heterogeneities have received new interest in reservoir simulations for CO 2 storage [17] and for geomechanical modeling describing effects of pore pressure during CO 2 injection [18].…”

Fault displacement modelling using 3D vector fields

“…Caumon et al [4], Lecour et al [11] and Holden et al [9] focus on stochastic perturbation of fault geometries and fault throw, but in a history matching workflow a deterministic way of perturbing the fault geometry and throw is desired. Effects of changing fault throw on reservoir flow can implicitly be represented by changing the throw used in the fault seal calculations as shown by Manzocchi et al [13], however, an explicit change of fault throw is needed for volume calculations and for well planning.…”