Ultra-Deepwater Riser Concepts for High Motion Vessels

10121-4204-01

Primary Performer
Stress Engineering Services, Inc. (SES)

Additional Participants
To be determined

Abstract
Researchers will determine an alternative riser arrangement that meets the demands of high motion vessels, yet that can be engineered, procured, installed, and commissioned at an acceptable cost delta over and above the Steel Catenary Risers (SCR). Several concepts exist which can potentially meet this goal. An initial comparative evaluation of each of these concepts should provide an indication of the concept which has the most potential. A risk assessment will help to confirm the selected candidate(s) system. It is anticipated that some form of testing will be required to mature at least one chosen concept to a level of being valid for use.

Research Objectives:

• Develop a fundamental technical understanding of the differences between existing riser concepts to the response of high motion vessels, such as semi-submersibles and ship shape FPSOs. Dynamic analysis will be used to to capture riser response to both high and low frequency motions in extreme and fatigue seastates.
• Develop a better understanding of the limitations of each riser concept and their causes. A risk assessment covering all phases of the riser’s life will be key to obtaining this knowledge.
• Assemble a meaningful testing plan, as agreed to between project industry participants and the U.S. regulatory agencies and carry out the testing within the agreed project schedule.

Project Description
SES researchers will develop a plan and perform assessments of (a) each riser concept with regard to behavior with high motion vessels (b) perform dynamic analysis of those concepts which warrant further examination for extreme seastates and (c) further analyze those systems with acceptable response in extreme seas to determine their response in fatigue seastates. Perform a risk assessment using historical data and all possible failure scenarios to provide a comparison with conventional SCRs. Validate the final concept with physical testing of key components within the load path and/or model test key assumptions relative to design requirements.

Impact of Project
Potential motion induced stresses and strains may affect the long-term integrity of the riser system putting the floating facility at risk of riser failure. This, in turn, puts the nearby environment and production rate at risk. The project expects to pre-qualify certain riser concept(s) as safe to use with high motion vessels, thus reducing riser risk and increasing safety to people, infrastructure and the environment, as well as ensuring an uninterrupted production rate.

Principal Investigator: Brian S. Royer

Project Cost:
DOE share: $1,200,000
Recipient share: $300,000

Project Duration: 3 years