Reliability by Design - HP/HT System Development
Authors: Harrold Dave , Ringle Dave , Taylor Michael , Timte Scott , Wabnitz Frank 
Published: October 2008

As the subsea industry moves into ultra deepwater, the need for higher rated completion equipment in terms of pressure, temperature and water depth is steadily growing and sets a case for increased reliability assurance. This paper illustrates an approach to reliability assurance and reliability demonstration. Besides discussing the unique challenges faced during the development of subsea completion systems for applications with shut-in wellhead conditions of up to 15,000 psi and 350Â°F and water depths to 10,000 feet, the paper outlines the approach to designing in reliability. It is shown how the deployment of a reliability assurance program influenced the development and qualification efforts to design in reliability and demonstrate reliability performance during the design phase. This paper will enhance the understanding for the need and the value of a stringent reliability assurance program for the development of new subsea systems.

Introduction

Regardless of their size and location, offshore projects today are faced with many unique and often times diverse challenges. Whether it is the requirement of a large upfront capital investment, a tight time schedule, dealing with uncertain reserves, addressing highly aggressive environments, or the dependence on unproven technology, all result in a higher level of risk exposure to the operator.

Today, the magnitude and consequences from these elevated risks are compounded by the state of the industry, which has seen two trends continue with regard to subsea developments. The first is the constant move into deeper and deeper water. Worldwide, the larger reserves of oil and gas that were located in the more accessible, and therefore, economically attractive shallow water regions are being depleted. This is leaving operators with the choice of pursuing either the remaining, economically marginal, shallow water finds, or moving into deeper water. Many are choosing deeper water. In the last two years, over twenty new deepwater discoveries have been made in the Gulf of Mexico alone, six of which are in depths that are greater than the current subsea completion record of 7,209 feet [1,2].

The economics of deepwater developments depend heavily on equipment performance, namely maintaining high system availability. For deepwater applications operators are routinely requiring system availability numbers in excess of 95% just to assure the projects remain economically viable [3,4]. Although achievable, these targets exceed what has typically been expected and has routinely been delivered to date in shallow water applications, which has been documented to be as low as 87% [5]. While the deepwater finds that are being developed tend to have much larger reserves with higher expected production levels, the upfront capital expenditures are also significantly higher due to the increased costs for exploration and development. Additionally, almost all of the deepwater regions in the world lack the necessary infrastructure required to bring these fields into production.

Therefore, the costs to put the entire system in place must be absorbed by the project. To be profitable in deepwater, the anticipated higher production rates not only must be realized but also maintained throughout the life of the project.