During 15 years’ development at Prudhoe Bay, some wells have been drilled near, or inadvertently through, faults, often resulting in impaired well performance. This paper provides examples of fluid movement through and along faults using open and cased hole logs, and production data. Where data exist, faults can be shown to be 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. Other problems result from drilling through fault zones including lost circulation, adverse hole conditions causing poor wireline log data and inadequate primary cementing. 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.

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