Systematic Technology Qualification for HPHT Subsea BOP Stack Equipment and System to Improve Safety, Reliability, and Availability

Abstract

The high-specification 18 ¾ blowout preventers (BOPs) of today have a maximum design pressure of 15,000 psi and a maximum design temperature of 250°F. However, the industry is preparing to push the threshold one step higher in both pressure and temperature. Existing 18 ¾ BOPs cannot accommodate new oil and gas discoveries that impose higher pressures and higher temperatures than the applicable American Petroleum Institute (API) standards can address. For many reasons, including safety, these high pressure and high temperature (HPHT) discoveries (>15,000 psi, >250°F) cannot be developed without design and manufacturing standards above and beyond existing standards and industry practice. However, developing these standards is difficult because the task requires the application of design methods not commonly used before in the industry. In this paper, a technology qualification methodology based on API and American Society of Mechanical Engineers (ASME) accepted design codes was used to define a design approach for HPHT subsea BOP stack equipment and systems. The methodology includes quantification by the development of equations and qualification by the development of processes. Design equations are validated by confirming that the appropriate API and ASME Boiler and Pressure Vessel Code (B&PVC) design standards are applied. Once defined, the correctness of their application is verified. Once the design is complete, other processes must be defined to assure that the design is manufactured, operated, and maintained as required. Qualification and acceptance-testing criteria are developed during the process per the existing API standards and additional requirements. Other API requirements used in conjunction with the manufacturer's procedures enable the BOP to be fabricated as specified. The BOP is but one component of a drilling system that must operate over time. Risk studies are required to confirm that the BOP, its controls, its supporting equipment, and the rest of the drilling system will operate within the required performance envelope. Additional risk studies will be defined in the development of maintenance procedures. The application of the methods described enable HPHT subsea BOPs to be designed and built using existing codes as well as newly defined methods. Other methods described in this paper examine the performance of BOPs and controls as an integrated system and how it can be best maintained. Design standards for HPHT BOPs can be drafted on a foundation of existing API and ASME codes and in conjunction with the methods identified. The development of design standards for HPHT 18 ¾” BOPs was inhibited by a lack of industry application and experience, as well as a lack of service history, but with new HPHT discoveries now in development, such standards are needed. This reticence to develop standards was further enforced by the absence of a clearly-defined design approach. This paper presents a methodology for qualifying this complex equipment that can be built and operated safely, so that the industry can continue to push the operational envelope of subsea development.