Drilling and evaluation services require repair and maintenance (R&M) programs to ensure that assets are returned to the fit-for-purpose state before their next application. R&M costs constitute a large percentage of the cost of service for an oil field services company. Consequently, there is a continuous " tactical" push to reduce R&M costs by increasing intervals, inspections, etc. To optimize a maintenance strategy, the cost of an on-rig failure or cost of failure (CoF) must be included. These costs include unplanned maintenance, lost asset utilization, transportation costs, variable labor costs, etc. The CoF indirectly includes the impact on the operator in terms of non-productive time (NPT) or unplanned downtime on the rig that could result in concessions or loss of contract. A reliability-centered maintenance (RCM) strategy provides a cost model that allows the service provider to consider internal cost reduction and customer impact.
This paper presents the RCM-based maintenance strategy currently being developed at Baker Hughes, and reviews the model and the tradeoffs that must be made between product costs (R&M costs) and the cost of a downhole failure (cost of failure) to the operator and the service company. As the applications become more difficult (deeper, hotter, higher pressures, etc.), and the cost of operations continues to rise, there is increasing pressure on the service companies to reduce the downhole failure rates and extend the useful lives of the rental assets to keep the R&M costs at a minimum. Not only is tracking individual part conditions and history important for implementing a traditional condition-based maintenance (CBM) strategy, but also the Cost of Failure for the service provider and operator is important.
Repair and maintenance is essential for a product to perform to its expected life. The fundamental question regarding repair and maintenance is whether to perform maintenance or to scrap. In many instances, there exists a trade-off between the cost of repair and the cost of part replacement, considering the remaining life of the product. This paper presents a life cycle cost (LCC) model for drilling and evaluation tools with a RCM approach for optimizing the repair and maintenance cycles that minimize the LCC. Throughout the paper, the term repair is employed for any corrective activity triggered by a failure, and the terms maintenance or preventive maintenance as an activity(s) for preventive measures.
For drilling and evaluation tools, Baker Hughes sets levels of maintenance in order to standardize workflow and logistics. For example, during Level I maintenance, the system is calibrated and measured for degradation and functionality. Level II maintenance replaces consumable parts such as seals. Level III maintenance rewires and replaces major parts such as the drive-shaft bearing based upon inspections or life predictions. To set the appropriate maintenance level, the Baker Hughes' preventive maintenance policy blends together time-based and environment-based maintenance. Scheduling maintenance is determined by a combination of job and waiting time, transportation, and environmental conditions (temperature, vibration, H2S, mud property, etc.). The policy takes into consideration factors that cause greater strains on the system and its components. The maintenance is conservatively scheduled in an attempt to discover failures before they occur in the field. After each maintenance activity the system may be assumed to be as good as new; however, maintenance is imperfect and does not truly restore the system to its original state (Ben-Daya & El-Ferik, 2008). Only specific components are replaced or rewired during maintenance, yet the whole system experiences deterioration throughout its lifetime. The entire system's degradation must be considered to fully assess the health of the system.