--> --> Abstract: Fault-Seal Evaluation in Exploration and Production Environments, by Graham Yielding, Pete Bretan, and Gary Marsden; #90914(2000)
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Graham Yielding1, Pete Bretan2, Gary Marsden3
(1) Badley Earth Sciences, Lincolnshire, United Kingdom
(2) Badley Earth Sciences
(3) Amerada Hess, Aberdeen, United Kingdom

Abstract: Previous HitFaultNext Hit-seal evaluation in exploration and production environments

Previous HitFaultNext Hit seal in sand-shale sequences is broadly predictable, since sealing Previous HitfaultNext Hit rock is generated by the sliding of different lithologies past one another. Potentially-sealing Previous HitfaultNext Hit rocks include clay smears and cataclastic gouges; clay-rich Previous HitfaultNext Hit rocks tend to form the better seals because they have smaller pore-throats. The first-order controls on Previous HitfaultNext Hit-rock development are the lithologies (clay content) in the faulted sequence and the amount of offset on the Previous HitfaultNext Hit. Input of this information to a simple algorithm (Shale Gouge Ratio, SGR) allows a prediction of the nature of the Previous HitfaultNext Hit rock at each point on the Previous HitfaultNext Hit plane.

In exploration/appraisal settings, the capillary entry pressure of the Previous HitfaultNext Hit-zone material is the critical parameter in determining whether a Previous HitfaultNext Hit can successfully form a side-seal to an accumulation. Published measurements on Previous HitfaultNext Hit-gouge samples show how entry pressures vary with clay content. Observations of in situ pressure differences across faults provide evidence for static seal below the entry pressure. Together, these datasets define a 'seal failure envelope' for Previous HitfaultNext Hit rocks of different compositions.

In production, the transmissibility (permeability/thickness) of the Previous HitfaultNext Hit zone is more important. Measurements on Previous HitfaultNext Hit-gouge samples show how permeability varies with gouge composition. Using the Shale Gouge Ratio, Previous HitfaultNext Hit-zone permeability can be mapped across the Previous HitfaultTop surface, providing a geologically-driven estimate of the transmissibility for input to reservoir simulation models. Using this methodology on a producing North Sea field gave an excellent history match after only 1 day of analysis (compared to several months of earlier work).

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana