Empirical Calibrations of Proven Sealing Faults

This paper discusses results of fault-seal calibration studies from ~70 well-constrained fields in 8 basins. Sealing faults were identified from proven differences in fluid levels, compositions, or gradients across seismically visible faults. Non-sealing faults were interpreted to occur when the fluid levels, compositions and gradients were all the same across the faults. Well and 3D seismic data were used to define both the structural and stratigraphic architecture of the fields, and to make fault plane juxtaposition diagrams of each fault. Each fault was subsequently gridded and contoured for both SGR (shale gouge ratio) and CSP (clay smear potential), and the results were compared to the buoyancy pressure differences across the faults.

Sealing sand-on-sand contacts were commonly observed in almost every major play regardless of sand-on-sand juxtaposition. Sealing critically-stressed faults and sealing thrust faults were also commonly observed. Leaking sand-on-shale contacts, although more difficult to conclusively document, are also observed. Faults from many different basins show a common first-order linear correlation of maximum seal capacity with the shale gouge ratio, regardless of in situ stress, degree of lithification, burial depth, or burial history. Surprisingly, faults in geopressured systems seal greater across-fault-buoyancy-pressure differences than faults with the same SGR values in normally pressured systems. Not all faults trap the maximum possible pressures, however. Calculations of SGR at well-log and seismic scales fail to capture the detailed heterogeneity of actual fault zones, and probability distribution functions