Fault Characterization and Reservoir Development at Kuparuk River Field, Part 2: Understanding Fault Zones and Predicting Fault Seal

By

R.W. Krantz and M.R Longden (Phillips Alaska, Inc.)

The production history at Kuparuk provides evidence of sealing or baffling faults. Some faults separate pressure cells, offset fault blocks with distinct oil-water contacts, and create barriers to effective EOR processes. Other faults with similar throw show little impact on fluids. At many drill-sites producing wells receive no support from adjacent injectors. Optimizing further development requires confident prediction of sealing faults.

Past efforts that focused on sand juxtaposition achieved only partial success. Evidence from core helps explain why. Core through fault zones shows both small faults with clay smear and larger fault zones with clay-rich gouge. These and other fault zone lithologies result in greatly reduced permeability. Thus even where sands may be present on either side of a fault, the intervening fault zone may itself create a barrier to fluid flow. Fault zone width increases with greater fault throw, and also contributes to fault seal probability. Our new characterization of faults begins with detailed fault mapping, especially fault continuity in three dimensions. Fault style models help guide the interpretation. We then integrate local stratigraphy and rock properties adjacent to the faults. Multiple techniques (shale gouge ratio, clay smear potential) determine the distribution of low permeability zones within the fault zones. Some of these are keyed to the deformation style differences between the early and later fault sets. Several case studies demonstrate this approach, and show more effective results in matching observed reservoir performance. These results can be applied at the scale of individual patterns or regional simulations.

AAPG Search and Discovery Article #90008©2002 AAPG Pacific Section/SPE Western Region Joint Conference of Geoscientists and Petroleum Engineers, Anchorage, Alaska, May 18–23, 2002.