Recent advances in rock bit seal technology have allowed greater predictability of bearing life. Cone loss following bearing failure incurs costs related to remedial activities. A risk analysis approach, utilising bearing life relationships and the inter-dependence of drilling events, is used to formulate a bit run cost optimisation method. The procedure enables a choice to be made between elastomeric and metal seals on a lowest replacement cost basis. The technique also provides a formal method for assessing the opportunity cost for employing a device for the downhole detection of bit bearing failures.

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