WEST is presenting at the 2007 Offshore Technology Conference. The abstract below summarizes the information. If you would like additional details, please contact us. To obtain a complete copy of this paper, visit OTC Papers Online.

OTC-18614-PP Using BOPs at Pressures in Excess of the Rated Working Pressure - A Solution for High Pressure Wells?

Description
As a result of a significant redesign of the Expro electro-hydraulic 15K psi Express Seven SSTT (Sub Sea Test Tree) due to customer requirements, Expro considered the review of an independent third party to be a useful design step. Accordingly, a risk assessment was contracted to help ensure the tool was deployed with reliability as high as reasonably practical. The process included: 1. Component level FMECA (Failure Modes, Effects, and Criticality Analysis) for hydraulic, electronic (hardware and software), and mechanical systems, 2. FMECA of most likely multiple failure situations, and 3. Fault trees of selected functionality.

Results and Conclusions
The design operating requirements included not only 15,000 psi, but also 121ºC maximum temperature. Electronic component selection included vendor qualification for the required temperatures and pressures. Wellbore wetted components had the added criteria of compatibility with completion fluids. In some instances, components could not be purchased to meet requirements, in which case qualification procedures were prepared and conducted under the SSTT vendor's direction. Where adequate standards did not exist for quality and reliability standards, those from other industries were utilized.

Over 1600 line items were generated to define component failures. These lines independently analyzed risks for each of four operating modes in the consequence categories of safety, environmental, and asset (economic), taking into account consequence severity, exposure, avoidance/mitigation, and likelihood of occurrence. Those items with SIL (Safety Integrity Level) 3 or greater were individually reviewed to determine if additional mitigation was required.

This paper will review the methodology, assumptions, and recommendations, as well as revisions that resulted. While the changes recommended were relatively few considering the depth and breadth of the analysis, all parties were in agreement that the objectives of design validation and risk reduction were accomplished.

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