07121- DW1402a

Goal
This project will assess alternative dry tree semisubmersible (DTS) concept designs for two different payload cases in accordance with an agreed upon basis of design, and select one hull form option for model testing and further development in a Phase 2 project. The intent is to investigate the feasibility of developing this platform design and to identify any technical limits to areas where further qualification or testing will be required. (Note: This project is one of two parallel efforts being undertaken. The other, Project 07121-DW1402b, is being conducted by another team led by Houston Offshore Engineering.)

Performers
FloaTEC, LLC, Houston, TX 77079
J. Ray McDermott Engineering, Houston, TX 77079-4526
Keppel Offshore & Marine, Singapore 629351
Vetco Gray, Inc., Houston, TX 77042
Seawell Americas, Inc., Houston, TX 77041
OTRC, College Station, TX 77845

Background
As Gulf of Mexico field development is rapidly moving to deeper waters, the available alternative platform concepts for dry tree drilling and production operations are limited. Without dry tree access, oil and gas production becomes subject to the availability and high cost of mobile offshore subsea drilling units, which in the current market are difficult and expensive to contract. Currently, the deepest tension leg platform (TLP) installed to date (Conoco’s Magnolia platform) is in 4,674 ft of water, whereas the Perdido Spar currently under fabrication is designed for installation in 8,000 ft water depth. As patent ownership for the Truss Spar limits the competition for spar platform developments to two companies, a competitive dry tree floating structure design (e.g. semisubmersible) is a needed option to provide greater flexibility for deepwater operators in making development decisions.

This project proposes to develop an ultra deepwater dry tree system concept for drilling and production in the GOM. The approach is to focus on an improved semisubmersible hull form that provides global motions competitive with Spar and compatible with conventional riser tensioning equipment and systems. The proposed hull concept will be composed of conventional hull structural components, may require proven installation/integration methods and will have been shown through global performance analysis to provide acceptable motions.

This Phase 1 project will develop payload and platform configurations for two study cases. The objective is to develop the configuration and perform a high-level assessment in terms of global motions, riser strokes, and constructability to support the decision making necessary to determine which concepts will continue into Phase 2. The project will develop the floating system concept, validate the concept through engineering analysis and model testing, and focus on engineering that will lead to rapid commercialization of the concept.

Deliverables will include a basis of design document, a payload summary table, a plan for the workshop to shortlist options, an interim report of initial hull and riser sizing, a report on the outcome from the shortlist workshop and selection of the model test option, model test results, a Phase 2 work scope, and a final report.

Potential Impacts
This project will accelerate the development of an alternative dry tree semisubmersible design that can be cost competitive with the current Spar alternative. This floating structure will utilize existing technology to accommodate large payloads, be permanently moored in deeper waters, and provide the global performance characteristics required for successful operation of a dry tree unit. More rapid development of such a technology will provide deepwater operators with greater flexibility in making development decisions, and will lead to more rapid production of domestic deepwater offshore oil and gas resources.

Accomplishments
After finalizing the topside layout, the team completed base case hull performance analyses for both the T-Semi and the E-Semi.The hulls were sized for the sensitivity case, and a hull global analysis was carried out. Both were shown to be feasible.

Current Status
Development of the Project Management Plan with a work breakdown structure that concisely addressed the objectives and approach for each task with all major milestones and decision points was completed. The development of a Technology Status Assessment describing the state-of-the-art of the proposed technology was also prepared. The key tasks undertaken following the submission of the Project Management Plan and Technology Status Assessment are outlined below.

Develop Basis of Design. The project team reviewed the General Design Criteria (GDC), identifying any additional information that may be required to perform the study in order to ensure that all platform motions, system component strength, and fatigue life can be assessed, and prepare process design data and assumptions including analysis of feed hydrocarbon, production profile, and conditions. Additionally, the team identified missing information required for assessing the riser responses and they proposed necessary design assumptions that are documented in the final Basis of Design.

Outline Study Options and Conduct Screening Study. Under this task, platform options were investigated. The project team developed payloads and deck layouts for each case investigated and designed the well bay layout. Riser sizing and payloads development were conducted as well as hull sizing for screening options. In addition, the team analyzed preliminary riser strength and completed the tensioner system initial design.

Constructability. A preliminary construction execution plan was developed for the various sizes of hulls and topsides to identify any limitations and ensure the feasibility of the proposed construction and installation methods.

Cost Estimate for Screening Options. The project team prepared a cost estimate to an accuracy of +/- 50% for each option. These cost estimates were compared with FloaTEC’s in-house cost database for Spar platforms to indicate the competitiveness of the DTS options with a comparable Spar.

Development of Selection Criteria for Shortlisting. Option selection criteria were developed in conjunction before holding a workshop designed to select payload options for model testing in a model basin facility. A number of areas were identified for comparison, and advantages and disadvantages were listed for each of the DTS options studied. Each design case was assessed separately to determine the best two options (one for each payload) to be carried forward to the next phase of the study.

Workshop to Short-list from Screening Options. A workshop was held with FloaTEC, its lower tier subcontractors, and RPSEA representatives. Attendees at the workshop were world class experts from end users having the knowledge to provide a constructive assessment of the screening process leading to a successful shortlisting process. The project team presented the screening study results and reviewed the ranking process. The presentation included details from the work for each of the areas identified above as part of the comparative process. A recommendation from the workshop experts was to discontinue further evaluation of the FloaTEC concepts at this point in the work and to not perform model tests on either concept. Both concepts were considered feasible.

Final Report. A final report for the work performed was prepared and submitted to complete work on this contract.

Project Start: December 5, 2008
Project End: December 31, 2009

DOE Contribution: $278,686
Performer Contribution: $115,829

Contact Information:
RPSEA – Jim Chitwood (jchitwood@rpsea.org or 713-372-2820)
NETL - Jay Jikich (Sinisha.Jikich@netl.doe.gov or 304-285-4320)
Performer Company – Jing G. Kuang, Ph.D. (jkuang@floatec.com or 281-870-5677)

Additional Information

Stage 1 Final Project Report [PDF-7.05MB]