An update on seismic reassessment of aging platforms offshore California

Several platforms offshore California, used for the production of oil and gas, are over 25 years old. The majority of these platforms were installed before industry-wide design methods and criteria were established. As a result of California's 1989 Loma Prieta earthquake, regulators have been developing a policy to address seismic reassessment of platforms offshore California. There are two questions about these aged platforms: (1) Are the structures fit-for-purpose? and (2) what types of monitoring and structural reassessment are required? After numerous public workshops, a consensus of what would constitute an acceptable level of fitness-for-purpose was developed. The final document has been approved by the American Petroleum Institute (API) and is now available. In addition to the guidelines, structural inspection and monitoring are an important aspect of maintaining the fitness-for-purpose of these aged structures. Structural inspection intervals are clearly specified in API RP 2A; damaged members can be accurately described in finite element models. So, the analyst can evaluate whether or not repair is mandated by a reduction in structural performance. In addition, the Minerals Management Service (MMS) has instituted a "Seafloor Earthquake Measurement System" (SEMS) to collect and analyze seismic data offshore. Many recently constructed platforms have accelerometers at various deck levels and having the free-field data available will provide the perfect calibration tool for post-event analyses. In order to verify that offshore operators have performed the reassessment adequately, the State and Federal regulators have instituted methods to check operators. The MMS has developed the "Certified Verification Agent" (CVA) program wherein a respected peer reviews the structural analysis/retrofit of the aged platform. At the State level, the California State Lands Commission has instituted an in-house review process, wherein the operator submits all structural information, including applied loading, configuration, and computer models, and the work is independently verified.