Assessment of Offshore Platforms in the Bay of Campeche. Application of the New Assessment Criteria
Authors: Rey L.E. , Bayazitoglu Y.O. , Valdes V.M. 
Published: October 2008

This paper summarizes the application of the new criteria for the assessment of fixed offshore platforms located in the Bay of Campeche, Mexico. The platform categorization process and the structural analyses performed are described. Design level analysis and ultimate strength analysis procedures and results are presented, which included the modeling of the damage, the application of the Load Reduction Factors (LRF's) and the calculation of the Reserve Strength Ratios (RSR's). For those platforms that exhibit inadequate deck height, calculation of the wave loading on the deck is described. Also, seismic assessment procedures and results are summarized. The results of these analyses were used to determine the fitness-for-purpose adequacy of seventeen PEMEX platforms located in the Southwest Marine Region of the Bay of Campeche.

Introduction

In October 1995, hurricane Roxanne passed through the Bay of Campeche (BOC). Platforms located in this area were subjected to extreme environmental conditions that put their physical integrity at risk. Special inspections after the storm indicated severe damage to some of the platforms. Initially, detailed assessment of the platforms were undertaken following the procedure given in Section 17 of Supplement 1 of the API-RP2A, 20th edition1 and the original design metocean criteria. The results indicated that five of the ten platforms selected for detailed analysis passed the assessment requirements for metocean loading. At that time, the results of the metocean studies performed by two different oceanographic consultants became available and considerable differences were noticed in their Hurricane Roxanne hindcast studies. This resulted in two different metocean criteria. One consultant reported that the design wave height (100-year storm) remains the same as the criteria used during the design of the platforms some twenty years ago, whereas the other recommended to reduce the metocean criteria. Consequently, Pemex Exploración y Producción (PEP) and the Instituto Mexicano del Petroleo (IMP) decided to perform a risk based oceanographic and earthquake study. Based on this study, PEP and IMP developed the "Transitory Criteria for the Design and Requalification of Offshore Platforms in the BOC2." Using this criteria, seventeen platforms were re-assessed. The work described in this paper illustrates the procedures employed in platform re-qualification using the PEPIIMP Transitory Criteria. This is the first application of the Transitory Criteria in conjunction with the guidelines given in APIRP2A. The results of the analyses will assist PEP and IMP to finalize the development of the Bay of Campeche design and assessment criteria.

Scope of Work for Platform Assessment

The scope of work for the platform assessment included:Gathering of platform informationParticipating in the special inspections programsAssessing the condition of the platforms, andDeveloping conclusions and recommendations regarding the mitigation alternatives for those platforms that do not meet the assessment requirements

Initially, a total of twenty-six platforms were selected for the assessment work. This represents approximately one-fourth of the total number of offshore platforms located in the Southwest Marine Region of the Bay of Campeche. The selection of the platforms was made by PEP and IMP based on the platform's damage, service type, geometric configuration, location and production levels.