across-Fault Seal Capacity Calibration against Shale-Gouge-Ratio (Sgr): Demonstrative Case Studies
Faults are commonly seen to support pressure differences (across fault pressure difference - AFPD) between juxtaposed reservoir units. Theoretically, for hydrocarbon leakage to occur across the entire width of a water-wet fault zone, the buoyancy pressure must exceed the threshold pressure on the highest formation water pressure side of the fault. Estimated SGR should be calibrated using the difference between the hydrocarbon pressure (on the relevant side of the fault) and the formation water pressure from the high hydraulic head side of the fault (i.e. highest aquifer pressure).
As part of an ongoing program of calibration, a data-set is currently being assembled. Preliminary results indicate that the use of the modified AFPD measurement results in a moderating effect on the global data-set. Hereafter selected case studies are presented which highlight the influence of the modified pressure measurement. Data-sets formerly having AFPD considered too low to influence the calibration plot now exhibit significant AFPD. Additionally, data which once exhibited very large AFPD and thus having potentially critical influence on the calibration envelope can be seen to be significantly reduced. In addition to being sounder theoretically, the resulting data-set calibrated using the alternative method for AFPD provides a better constrained SGR-AFPD correlation envelope.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009