The extensional Berge fault (Devonian Kvamshesten Basin, West Norway) displays 430 m of syntectonic stratigraphy with fluvial sandstones and red fines exposed in a hanging wall growth section. The fault consists of three linked strands, where the offset diminishes and tips out stratigraphically upwards. Folds in the growth basin include a rollover and drag fold that record cumulative deformation during the main phases of fault slip, and a monocline that records the death and burial of the fault. Deformation styles in both the subbasin fill and the fault core indicate that the sediments were unconsolidated to poorly lithified during deformation. The upward-narrowing fault core consists of indurated breccias derived from footwall conglomerates, and mainly laminated fault gouge of subbasin affinity. Towards the hanging wall there is a mixed layer of sandstone lenses enclosed in fault gouge; this unit is variably sheared. In the damage zone deeper in the subbasin, truncating-style small-scale tabular shear bands show a general increase in frequency towards the fault, with abundant peaks in frequency next to the fault core. Smearing-style shear bands are merely encountered near the master fault. In the upper monocline realm, an overall broad zone of deformation reveals a moderate frequency of shear bands, characterized by clear distinctions between variably deformed layers. Some tabular dilation structures are found locally as layer-confined strain throughout the basin.We reason that the mixed layer is a product of fluid mobilization in/along the fault core. Fluid induced weakening combined with differential compaction would augment aseismic creep, as advocated for the creation of the smearing shear bands. We discuss a conceptual model in which damage zones grow by repeated rejuvenation and expand during propagation events, advocating that a distinctive damage zone becomes better expressed with increasing faulting events and depth (consolidation) in a growth basin. (C) 2012 Elsevier B.V. All rights reserved.

Faults in nature commonly affect surrounding rock volumes and can as such be described as fault envelopes with a given internal geometry and architecture. Modeling techniques currently employed when modeling faults in petroleum reservoirs are mostly two-dimensional (2-D); hence, a need is present for more accurate and realistic description and quantification of deformational architectures and properties to accurately predict fluid flow in fault zones.Fault facies (FF) modeling is a concept for three-dimensional (3-D) fault zone characterization, facies modeling of fault rocks and fluid flow simulation, which is presented here and demonstrated by the use of a synthetic fault model. FF modeling is performed by first generating a 3-D grid of the fault envelope, which includes the conventional fault plane. Second, a kinematic strain calculation is executed in the FF grid. The strain parameter is used to calculate a fault product distribution factor (FPDF), which describes the fault displacement in the fault envelope. This parameter together with strain distribution is subsequently used to condition the fault model for facies modeling. Finally, FF modeling is executed. To achieve adequate flexibility and realism, pixel-based modeling is combined with object-based modeling methods to populate the FF grid with facies.This synthetic model shows that it is possible to honor structural outcrop observations in fault zones, and FF modeling is able to produce realistic looking fault zone deformation structures in 3-D. It is possible to implement faults with varying width and displacement, although the FF grid itself has a regular fixed width. This is highly advantageous as compared to controlling the fault geometry with the grid itself. We propose that FF modeling can improve fault zone characterization and also capture fluid flow uncertainty in fault zones in a more realistic way than is possible with 2-D methods.

This article describes an algorithm to compute finite strain in faulted corner point grids using the software Havana. The algorithm is based on a simple fault displacement formula, and a volumetric computation of strain in the grid's deformed configuration. The volumetric computation of strain is tested by comparing the finite strain of a 3D trishear model calculated by this method, with that calculated by the tetrahedrons method. The agreement between both methods confirms the validity of the volumetric strain computation. The algorithm is applied to synthetic models of one and three intersecting normal faults, and to a real model with seven faults, the Emerald Field. In all cases the computed finite strain is consistent with the fault network and with the variation of slip along the faults. There is one parameter that affects the computation significantly: the drag radius ( r d ) or extent of folding across a fault. Low r d models yield high finite strain and strain gradients but limited fault interaction, and vice versa. Using empirical relations between fault throw and damage zone width, r d can be narrowed down and further constrained by evaluating the quality of the grid's restoration. The strain algorithm can be integrated easily into a reservoir modelling workflow and in stochastic modelling. The algorithm provides criteria for conditioning the distribution of deformational features within the reservoir zones affected by faulting, based on the magnitude of finite strain.

Fluid flow simulation models of faulted reservoirs normally include faults as grid offset in combination with 2D transmissibility multipliers. This approach tends to oversimplify the way effects caused by the actual 3D architecture of fault zones are handled. By representing faults as 3D rock volumes in reservoir models, presently overlooked structural features may be included and potentially yield a more realistic description of structural heterogeneities. This paper investigates how a volumetric fault zone description, will affect fluid flow in simulation models. An experimental 3D model grid including a single normal fault, defined as a volumetric grid, was constructed. Subsequently, the fault grid was populated with two conceptual fault deformation products – sand lenses and fault rock – using an object-based stochastic facies modelling technique. In order to evaluate the effect of varying petrophysical properties, fault rock permeability and sand lens permeability were varied deterministically between 0.01 mD and 1 mD and 50 mD and 500 mD, respectively. The impact of fault core architecture was investigated by deterministically varying sand lens fraction and sand lens connectivity. This yielded 24 model configurations, executed in 20 stochastic realizations each. Fluid flow simulation was performed on 480 model realizations. Simulation results show that the most important parameters influencing fluid flow across the fault were fault rock matrix permeability, and whether or not the sand lenses were connected to the undeformed host rock. Sand lens permeability and sand lens fraction turned out to be less important for fluid flow than fault rock matrix permeability and sand lens connectivity.