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Abstract
Access to 3D descriptions of fault zone architectures and recent development of modeling techniques allowing explicit rendering of these features in reservoir models, provide a new tool for detailed implementation of fault zone properties. Our aim is to assess how explicit rendering of fault zone architecture and properties affects performance of fluid flow simulation models. The test models use a fault with a maximum 100 m displacement and a fault damage zone with petrophysical heterogeneity caused by the presence of deformation bands. The distribution pattern of deformation bands in fault damage zones is well-documented, which allows generation of realistic models. A multiscale modeling workflow is applied to incorporate these features into reservoir models. Model input parameters were modulated to provide a range of property distributions, and the interplay between the modeling parameters and reservoir performance was analyzed. The influence of deformation-band damage zone on reservoir performance in the presence of different fault core transmissibility-multipliers was investigated. Two configurations are considered: one in which the fault terminates inside the model domain, representing a case in which the fluid can flow around the fault, and one in which the fault dissects the entire model domain, representing a case in which the fluid is forced to cross the fault. We observed that the impact of deformation-band fault damage zone on reservoir performance changes when the fault core transmissibility multiplier is changed. Reservoir performance is insensitive to changing damage zone heterogeneity in a configuration in which flow can move around the fault. Where flow cannot bypass the fault, the influence of fault damage zone heterogeneity on reservoir performance is significant even when the fault core transmissibility multiplier is low.
Highlights
Our results suggest that the presence of a fault damage zone appears to affect flow patterns in these instances because unswept oil can be observed in the footwall damage zone (Figure 9). This effect cannot be modeled by the implicit modeling method, which uses a reduced fault transmissibility multiplier value to capture the flow effect of a baffling fault damage zone; as Figure 9f shows, the effect of unswept oil in the down-flow side of the fault is not captured by the fault core transmissibility multiplier (FTM)-only model even though an extremely low value of zero is used
The results show that reservoir performance is not sensitive to the variation of an FTM in damage zonepresent models (Figure 7)
We have investigated the impact of incorporating a field-scale 3D fault damage zone on simulated fluid flow using two scenarios: one in which fluid is allowed to flow around the fault zone and one in which fluid is forced to move through it
Summary
Since the 1970s, fault damage zones dominated by millimeter- to centimeter-thick deformation bands have been identified in outcrops and core data worldwide (Aydin, 1978; Antonellini and Aydin, 1994, 1995; Fossen and Hesthammer, 1997; Shipton and Cowie, 2001, 2003; Fossen and Bale, 2007; Fossen et al, 2007; Cilona et al, 2012; Schueller et al, 2013). Other workers have addressed the scaling relationship between damage zone width and fault displacement (Knott et al, 1996; Beach et al, 1999; Fossen and Hesthammer, 2000; Shipton and Cowie, 2001; Schueller et al, 2013), and how deformation band properties are controlled by tectonic regime, host rock lithology, and burial depth (Ballas et al, 2014, 2015; Soliva et al, 2016). The same study concludes that the impact on effective permeability is limited, and controlled by the cumulative thickness of deformation bands and their 3D connectivity
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