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[[Fault]]s play an important role in creating hydrocarbon traps. For a better appreciation of the risks associated with fault-controlled prospects and of the production from faulted fields, it is important to understand the processes that contribute to fault seals. Given certain information about a fault cutting a reservoir sequence, it is desirable to predict the likely [[Fault seal behavior|sealing behavior]] of each part of the fault system.

[[Fault]]s play an important role in creating hydrocarbon traps. For a better appreciation of the risks associated with fault-controlled prospects and of the production from faulted fields, it is important to understand the processes that contribute to fault seals. Given certain information about a fault cutting a reservoir sequence, it is desirable to predict the likely [[Fault seal behavior|sealing behavior]] of each part of the fault system.

 

==Shale smear factor==

===Shale smear factor===

Lindsay et al. (1993) described outcrop studies of shale smears in a Carboniferous fluvio-deltaic sequence. In contrast to the sequence described by Weber et al. (1978), these rocks were lithified at the time of faulting (burial depth about 2 km). Lindsay et al. (1993) recognized three types of shale smear: shear, abrasion, and injection.

Lindsay et al. (1993) described outcrop studies of shale smears in a Carboniferous fluvio-deltaic sequence. In contrast to the sequence described by Weber et al. (1978), these rocks were lithified at the time of faulting (burial depth about 2 km). Lindsay et al. (1993) recognized three types of shale smear: shear, abrasion, and injection.

Figure 2-Smear factor algorithms for estimating likelihood of clay smear on a fault plane. (a) Clay smear potential (CSP) (Bouvier et al., 1989; Fulljames et al., 1996) given by the square of source-bed thickness divided by smear distance; (b) generalized smear factor, given by source-bed thickness divided by smear distance, with variable exponents; (c) shale smear factor (SSF) (Lindsay et al., 1993) given by fault throw divided by source-bed thickness. Methods (a) and (b) model the distance-tapering of shear-type smears, whereas method (c) models the form of abrasion smears.

Figure 2-Smear factor algorithms for estimating likelihood of clay smear on a fault plane. (a) Clay smear potential (CSP) (Bouvier et al., 1989; Fulljames et al., 1996) given by the square of source-bed thickness divided by smear distance; (b) generalized smear factor, given by source-bed thickness divided by smear distance, with variable exponents; (c) shale smear factor (SSF) (Lindsay et al., 1993) given by fault throw divided by source-bed thickness. Methods (a) and (b) model the distance-tapering of shear-type smears, whereas method (c) models the form of abrasion smears.

===Shale gouge ratio (SGR)===

==Shale gouge ratio (SGR)==

The shale gouge ratio is simply the percentage of shale or clay in the slipped interval. Figure 3a illustrates how this would be calculated, at a given point on a fault surface, for explicit shale beds

The shale gouge ratio is simply the percentage of shale or clay in the slipped interval. Figure 3a illustrates how this would be calculated, at a given point on a fault surface, for explicit shale beds

Figure 3-Gouge ratio algorithms for estimating likelihood of clay entrainment in the fault gouge zone. The gouge ratio reflects the proportion of the sealing lithology in the rock interval that has slipped past a given point on the fault. (a) Calculation for explicit shale/clay beds in an otherwise shale-free sequence; Dz is the thickness of each shale bed. (b) Calculation for a sequence of reservoir zones; Dz is the thickness of each reservoir zone and Vcl is the clay volume fraction in the zone.

Figure 3-Gouge ratio algorithms for estimating likelihood of clay entrainment in the fault gouge zone. The gouge ratio reflects the proportion of the sealing lithology in the rock interval that has slipped past a given point on the fault. (a) Calculation for explicit shale/clay beds in an otherwise shale-free sequence; Dz is the thickness of each shale bed. (b) Calculation for a sequence of reservoir zones; Dz is the thickness of each reservoir zone and Vcl is the clay volume fraction in the zone.

===Smear gouge ratio (SGR)===

==Smear gouge ratio (SGR)==

Smear-gouge ratio is the ratio of sand to shale that has moved past some critical portion of the fault plane (Skerlec, 1996). Although not simply relatable to the shale gouge ratio, the smear gouge ratio varies in an inverse manner; i.e., high shale gouge ratio corresponds to low smear gouge ratio and vice versa.

Smear-gouge ratio is the ratio of sand to shale that has moved past some critical portion of the fault plane (Skerlec, 1996). Although not simply relatable to the shale gouge ratio, the smear gouge ratio varies in an inverse manner; i.e., high shale gouge ratio corresponds to low smear gouge ratio and vice versa.