Faulting: A Major Control on Fluid Flow and Production Performance, Prudhoe Bay Field, Alaska
KAY, ALEXANDRA, DIRK BODNAR, and EDWARD CAZIER, BP Exploration (Alaska) Inc., Anchorage, AK
During 13 years of development at Prudhoe Bay, several wells have been drilled near, or inadvertently through, faults, often resulting in impaired production performance. This paper provides examples of fluid movement through and along faults using open and cased hole logs and production data.
The crest of the Prudhoe structure is relatively unfaulted. In contrast, peripheral areas are densely faulted, with large-throw northwest-southeast normal faults, complexly linked east-west and north-south trends.
Most faults are transmissible where reservoir juxtaposes reservoir. Data from recently drilled wells show pressure communication across major faults. Highly transmissible fault planes allow rapid movement of water or gas to the perforated intervals of production wells. Faulting is the major route for aquifer influx through the bottom-sealing tar layer. Fault-related gas influx from the expanding gas cap has caused diminished oil production, as well as shut in at high gas-oil ratios. Faults provide vertical communication for injected gas and water to perforations in the oil column. Rapid waterflood breakthrough along faults from injectors to producers bypasses oil in places.
Lost circulation, adverse hole conditions causing poor wireline logs, and inadequate primary cementing may result from drilling through fault zones. These problems result in increased wellwork, lost production, and occasionally, the need for redrills, all of which increases cost. The majority of wells are unfaulted in the reservoir section, but with continued infill drilling, targeting new wells to avoid faults becomes increasingly difficult. The importance of accurate structural mapping tied to well data, therefore, cannot be overstated.
AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)