This paper demonstrates the positive results of conducting a risk-based total system review of an Integrated Active Heave Hoisting System used on Deepwater Drilling Vessels. This was accomplished by carrying out a 'failure mode and effect analysis' (FMEA's) study on the major sub-systems of the Hoisting System with focus on the interaction of all the components and their integration into one system. The analysis was carried out with significant involvement from the rig owner, the designers/manufacturers, and an independent third party each providing extensive input to the study, thus providing a broader spectrum of opinions and knowledge of the entire system.
The results of this study are multifold: a significant reduction of the risk of major accidents due to component failures within the system, an increased reliability and availability of the system, improved rig owner understanding of the system (and thus informed decisions on equipment usage and on the establishment of operating limits of the system and the rig), and an overall increase of confidence in the system provided.
The average day rate of modern deepwater drilling and production mobile offshore units ranges between ﹩200k and ﹩300k. That translates to roughly ﹩10,000 per hour. There are major economic losses when the rig loses uptime. Accidents and equipment failures can significantly affect uptime depending on the effect on personnel, environment, equipment, the well, etc. The consequence costs can escalate from the tens of thousands of dollars into the hundreds of millions or more.
To avoid these scenarios a proactive approach was utilized for the new GlobalSantaFe Deepwater Drilling vessels (Development Driller I and II). An independent third party was engaged to conduct a total system review of the integrated active heave hoisting system with the intention of issuing a "Fit for Purpose" statement. DNV's Offshore Standard DNV-OS-E101 "Drilling Plant", October 2000 was used as a measure to evaluate the integrated hoisting system against.
Some codes and standards have been developed to help ensure that the design of drilling systems meets a minimum standard (e.g. DNV's Offshore Standard DNV-OS-E101 "Drilling Plant", October 2000). Unfortunately the development of technology outpaces the rate at which these standards are generated. Furthermore, economic pressures and competition force companies into adopting and including technology advancements as fast as they surface. Tools such as failure mode and effects analysis1 (FMEA) and other risk assessment practices should be used to proactively identify shortcomings that may have otherwise gone unnoticed. Furthermore, these tools offer excellent opportunities for design optimization with respect to lifecycle costs.
Since so much is at stake with these modern systems (asset value and cost of an accident or unplanned rig downtime) often system designers are confronted with making "million dollar" decisions. Through quantification and factual understanding of the costs of a design change and benefit of the change, sound economic decisions can be made.
Risk assessment practices are about anticipating failures (and their consequences) and taking planned, rehearsed steps to improve the system and to protect stakeholders' interests.
