Quantitative Fault Seal Analysis
Fault seal behavior of normal faults in most hydrocarbon basins is dependent upon the ratio of sand/shale in the fault zone. Faults with sand-rich gouge tend to leak; faults with shale-rich gouge tend to seal. The estimated sand/shale ratio is the SGR, or SMEAR GOUGE RATIO. The SGR is calculated from the total thickness of sand and shale that has moved past a point along the fault.
The SGR required for seal or leak is determined empirically by analyzing faults in existing fields. Our growing database now includes more than 400 faults and provides highly predictable control over seal behavior. In the Gulf Coast 97% of all faults analyzed obey this simple relationship between gouge composition and seal behavior.
Calculation of SGR
The diagram below shows how the SGR is calculated as a sand, Rd, moves along the fault with progressive throws of 10, 100, and 250 ft. In each case the SGR is equal to the thickness of sand divided by the thickness of shale that Rd has moved past. This stratigraphic interval that Rd has moved past is shown in red.