Quantitative Risk Assessment as a Design Tool - Recent FPSO Experience
- R.E. Overfield (ExxonMobil Development Co.) | J.F. Collins (ExxonMobil Production Co.)
- Document ID
- Society of Petroleum Engineers
- SPE Production & Facilities
- Publication Date
- May 2002
- Document Type
- Journal Paper
- 72 - 77
- 2002. Society of Petroleum Engineers
- 4.5 Offshore Facilities and Subsea Systems, 5.4.2 Gas Injection Methods, 7.2.1 Risk, Uncertainty and Risk Assessment, 5.8.5 Oil Sand, Oil Shale, Bitumen, 7.2.2 Risk Management Systems, 4.1.4 Gas Processing, 4.5.3 Floating Production Systems, 4.2.4 Risers, 6.5.5 Oil and Chemical Spills, 4.1.5 Processing Equipment, 4.1.2 Separation and Treating, 4.1.9 Heavy Oil Upgrading, 4.2.5 Offshore Pipelines, 4.2 Pipelines, Flowlines and Risers, 7.2.5 Emergency Preparedness and Training, 4.2.3 Materials and Corrosion, 1.6 Drilling Operations, 4.5.4 Mooring Systems, 4.5.7 Controls and Umbilicals
- 0 in the last 30 days
- 522 since 2007
- Show more detail
- View rights & permissions
|SPE Member Price:||USD 5.00|
|SPE Non-Member Price:||USD 35.00|
Quantitative risk assessment was used as a tool for the conceptual and detailed design of two floating production, storage, and offloading (FPSO) installations. Results from the risk-assessment study were used to identify significant risk contributors that influence the design and operation of the facilities and to demonstrate that the risk-acceptance criteria adopted by the company were met. The results were also used to identify opportunities to further reduce the risk to a level that is as low as reasonably practical (ALARP).
Traditional risk, reliability, and consequence analysis methods were used to evaluate impacts from process and marine facilities and to determine the design of accidental loads during the conceptual engineering and design phases. Results were used as data for a detailed fault-tree analysis of accident scenarios and used to set the design criteria for significant structures and facilities.
In addition, analyses of subsea facility interfaces and field operations were performed to incorporate the full development scope. Particular attention was given to subsea pipelines and flexible risers as well as tanker operations and their effects on FPSO operation and design.
Event frequencies were determined from industry data and conditioned for the special design and operating features of the chosen FPSO concept. Risk sources, impacting fatal accidents, impairment of safety functions, and loss of asset value, were quantified for use in demonstrating an acceptable level of risk and to test opportunities to further reduce operating risks.
Results from the analyses show that process fires and explosions dominate the risks to personnel and safety functions, followed by cargo tank explosions. Tanker collisions, subsea pipeline and riser leaks, and turret operations were found to represent significant asset risks. Design development and operations planning efforts focused on these areas to reduce risk and improve reliability.
Esso Norge AS, a subsidiary of ExxonMobil Corp., recently started up two FPSO-type facilities offshore Norway. As required by Norwegian regulations and operations integrity-management system, risk assessment was applied as a design tool to elucidate the relative risk contributions of hazards and to ensure that individual risks were correctly understood and mitigated. Also in keeping with the Norwegian Petroleum Directorate's (NPD) regulatory requirements and the operator's risk-acceptance criteria, riskassessment results were used to identify opportunities to reduce risk further under the ALARP principle.
Both FPSOs are new builds that were designed and constructed under Engineering, Procurement, Construction, and Installation (EPCI) contracts. Risk-assessment studies of the FPSO vessels were performed by the main contractors under subcontracts to specialized risk-analysis companies. The operator's projectmanagement teams performed additional field-specific risk analysis and integrated all risk studies into a total risk assessment (TRA) that covered each development. A timeline for the risk studies is shown in Fig. 1.
The Balder floating production unit (FPU) design and construction was under way when an agreement was formed to increase the production capacity and complete the FPSO for operation on the Norwegian continental shelf. In the course of technical verification reviews, it became apparent that additional analysis was needed to support design decisions and to demonstrate compliance with Norwegian regulations. Additional risk and consequence studies were completed to provide support for verification of the modified design and to demonstrate compliance with the NPD's regulations relating to the use of risk analysis in the petroleum activities and explosion- and fire-protection regulations. The findings were used to complete the modification work and to correct deficiencies found in the integration of the original and the modified designs.
During the Jotun development project, teams of designers, operators, and risk analysts identified major hazards and mitigation methods, beginning in the conceptual design process. Concept safety evaluation (CSE) was used in the front end of the engineering phase to make a coarse assessment of the risk level each hazard represented to the operation. Risk studies addressed all aspects of the field-development concept, including drilling, production, marine operations, offloading operations, and subsea design. During detailed engineering, the CSE was further refined with quantitative risk assessment (QRA). QRA results were used to verify risk levels relative to risk-acceptance criteria and to provide a tool to support decision making for the evaluation of technical and operational measures to control risk. Quantitative risk levels were analyzed recursively along with the maturation of the design. This provided an opportunity to use the results to guide engineering design decisions as they were being made. Hazard registers were updated and used as the basis for emergency preparedness analysis and plans.
Differences in design features between the Jotun and Balder facilities created an opportunity to compare and contrast the relative magnitude of risk contributors. QRA is an evolving science, and the numerical results may reflect differences in interpretation or emphases between analysts. Differences in assumptions about a given risk may cause assessment results to differ by a factor of two or more1 under otherwise identical circumstances. For this reason, absolute comparison of the quantitative results has not been made between Jotun and Balder. Relative contributions, which reflect the internal consistency in each study, are used instead.
|File Size||1 MB||Number of Pages||6|