Risk Assessment & Management Based Hurricane Wave Criteria for Design and Requalification of Platforms in the Bay of Campeche

Abstract

Abstract This paper summarizes risk based hurricane wave criteria that have been developed for design and requalification of Petroleos Mexicano (PEMEX) platforms in the Bay of Campeche. Probability based Risk Assessment and Management (RAM) methods were used to characterize operating and environmental loadings and platform loading capacities. Results from recent field tests were used to verify the loading and capacity analytical models used in this study and to characterize the biases and uncertainties in these models. Characterization of the metocean conditions were based on results from a study performed by Ocean weather Inc. The American Petroleum Institute (API) wind, wave, and current loading models were used to determine the loadings associated with extreme condition hurricanes. The ULSLEA (Ultimate Limit State Limit Equilibrium Analyses) platform capacity model was used to determine the capacities of new and existing platforms. This included recognition of the time dependent loading and nonlinear platform capacity characteristics. Design and requalification 'target reliabilities' were based on economic, historic performance, and standards-of-practice approaches. Three platform classifications were developed that reflect different consequences associated with loss of safety or serviceability functions. Performance characteristics of the platforms in the Bay of Campeche during hurricane Roxanne were used to verify the computed reliabilities. Following approval of the target reliabilities by the management of PEMEX, the platform design and requalification guidelines were developed by Instituto Mexicano del Petroleo (IMP). Special studies were conducted to refine analytical models and characterizations associated with interactions of the hurricane waves with the soft sea floor soils, wave-in-deck forces, the capacities of new, damaged, and repaired tubular joints, the fatigue of tubular joints and appurtenances, and the stiffness and capacities of laterally and axially loaded piles. Working Stress Design (WSD), Load and Resistance Factor Design (LRFD), and Ultimate Limit State (ULS) platform design and requalification guidelines were developed. This paper summarizes the guidelines that were developed for hurricane ULS and WSD evaluations. Introduction At the present time, there are more than 200 platforms located in the Bay of Campeche (Fig. 1). These platforms produce in excess of 2 million barrels of oil and 1.5 billion cubic feet of gas per day. The majority of the platforms are located in water depths between 30 m and 50 m. Most of these platforms were installed in the 1980's and 1990's, with some platforms installed in the late 1970's. In October 1995, hurricane Roxanne formed in the western Caribbean Sea, crossed the Yucatan Peninsula, and entered the Bay of Campeche. Due to a southward moving front, the hurricane did not follow the normal northerly path of most hurricanes. It was forced back into the Bay of Campeche and the eastern coast of Mexico where it did considerable damage. Roxanne was the most severe hurricane to affect the Bay of Campeche during this century. It generated environmental conditions which approximated those of 100-year return period hurricanes.1,2 Offshore, the majority of damage was confined to pipelines.3 There was some damage to platforms, but in general, these structures performed very well. Following Roxanne, PEMEX initiated an extensive inspection of the platforms in the Bay of Campeche. Some damage to the platform structures were found.