The Gulfstar FPS, a three-deck, wet-tree spar, is a standardized design with oil and gas gathering, production handling, gas processing,and an export pipeline. The design is expected to be used on other projects bringing about considerable economic benefits. Perry Fischer reports.
Discovered in 2003 on Mississippi Canyon block 725 using Transocean’s Deepwater Horizon semisubmersible, the Tubular Bells prospect is under development by Hess Corp. Tubular Bells lies mostly on MC726 in the US Gulf of Mexico, about 135 miles southeast of New Orleans in 4300-4600ft of water. Government permits have been finalized for the $2-3 billion project, all the major contracts have been signed and drilling is underway.
Williams Partners is building a classic, standardized floating production spar called Gulfstar, plus associated gathering and export lines for Hess and its partner Chevron.
The development plan is for two subsea drill centers to tie back to the spar. Nine wells were batch-set in 2012. Hess has contracted the Stena Forth drillship to complete the drilling activities. Hess is the operator of Tubular Bells with a 57.14% interest; the remainder is held by Chevron USA.
About the field
The Tubular Bells prospect was discovered in late 2003. the field is in the lauri sub-basin and is a deep Miocene discovery in an area with many recent discoveries and undrilled prospects (Figure 1). The discovery well – operated by BP, the original major partner before selling its interest to Hess and Chevron in late 2010 – was drilled to a +30,000ft TD and discovered hydrocarbon pay. An appraisal well was drilled in 2006 and found hydrocarbons five miles from the discovery well.
BP drilled two more appraisals (sidetracks) in 2006/07. The results showed an elliptical shaped field that spanned portions of six blocks. The Gulfstar facility has a design capacity for 60,000b/d oil and 135mmcfd gas production, with recoverable oil and gas reserves at Tubular Bells estimated at more than 120mmboe.
The geological and geographical setting of the field is such that infrastructure developed for Tubular Bells will be used to develop other nearby discoveries. Only 17 miles of export pipeline from Tubular Bells are required to tie into William’s Canyon Chief gas pipeline and the Mountaineer pipeline.
Putting it all together
First and foremost in the project is the central processing facility, which will be installed in MC724. Williams Partners will design and construct the central facility, called Gulfstar FPS – a classic, three-deck, wet-tree spar design (Figure 2) – including oil and gas gathering, production handling, gas processing services and the export pipelines. Williams Partners is a diversified MLP (master limited partnership) in the business of processing natural gas and liquids, and transporting oil, gas and NGLs. It currently transports about 14% of US natural gas. It will own the topsides/spar facility while Hess will operate it.
Williams’ Stafford Menard, manager for Gulfstar, says the FPS is a ‘first’ in many respects. Although there has been a cell spar built, it’s the first spar, classic or truss, to be built in the US. Williams expects to deliver the facility by mid-2014.
Helping to achieve the fast delivery, Williams will be building all of Gulfstar’s major components on the US Gulf Coast, with more than 90% of the materials and sub-components sourced in the US, and coming from about 20 American states. This will create about 1000 jobs. The major components, the hull and topsides, are being built at Aransas Pass, Texas, and Houma, Louisiana, respectively.
Williams expects Gulfstar’s standardized design to be used economically on other projects with design requirements similar to Tubular Bells, including 3000-8500ft water depths and compliance with new maximum storm specifications.
Given the water depths, the long offsets to the hub and substantial length of the flowlines (Figure 3), flow assurance will be a significant design consideration. Gulfstar will have a variety of flow assurance chemicals employed, including onboard storage for over 1100bbl of methanol, and other flow-assurance chemicals such as asphaltine and paraffin inhibitors. There is also storage for more than 10,000bbl of high quality, treated ‘dead oil’ onboard the spar that can be used to fill and preserve flowline functionality in the event a shut-in is required.
The spar-based FPS will have 60,000b/d of oil handling capacity and 135mmcf/d of gas capacity (with the potential to expand to 200mmcf/d), and provide seawater injection services.
Wood Group’s Alliance Engineering was awarded an engineering and design contract for the topside decks and facilities. The three-deck topsides include processing and seawater-injection equipment, utilities, personnel accommodations, pumping and gas compression for export, and a helideck. The topsides will weigh about 7000 tons when completed.
A McDermott International subsidiary was selected by Williams for the transportation and installation of the spar hull and its moorings. McDermott’s DB50 vessel will install the moorings before installing the spar and a temporary work deck.
Hess contracted Technip to design, engineer, fabricate and install more than 28 miles of subsea flowlines, pipeline terminations, steel catenary risers, and piles and associated structures. Technip’s deepwater pipelay vessel Deep Blue is due to complete the work this year.
It’s been recognized that models remove any misconceptions between partners and stakeholders, and are useful to visualize surface and subsurface layouts. Williams used C-Ray Media to model and animate its Gulfstar project. The video, which is posted on Williams.com, highlights Gulfstar’s quick construction and other features.
After seeing the Gulfstar video, the project team at Hess commissioned a similar model as a visual tool for internal project management reviews and partner meetings. Hess worked with Williams to combine the offshore campaign and subsea field layout with the existing Williams animation to create a complete project scope. A brief portion of the Hess subsea field animation is captured in the Williams video.
‘Collaborating with Hess seemed like a natural fit, since they are one of our biggest customers,’ says Stafford Menard, manager of Gulfstar development for Williams. ‘The result was a great piece of animation that tells the Gulfstar story visually.’ He adds: ‘We use it for different reasons, but it’s been especially helpful when we do trade shows and for the investment community. We often run into people who have a limited background in offshore technology, and the animation shows what we’re building, how all the parts fit. It puts it into scale and shows why the investment is what it is.’
‘Such highly technical, complex animation projects often require more time and research than expected,’ says Jason C Olson, senior project engineer for Hess. ‘Collaborating helped both companies save valuable time while producing a better end result. I highly recommend that companies consider partnering with their affiliates when working on a large field model . . . start early and take the time to understand your partner’s goals and objectives so that you can split and concentrate your efforts.’
Tubular Bells and Gulfstar FPS illustrate the need for mid-sized field development and standardized design. Similar to the larger Independence Hub project that came before, the general expansion of infrastructure is to develop even smaller fields in the future.
This development is another example of the ‘hub and spoke’ concept. Williams’ Menard puts it this way: ‘Infrastructure development is a major part of our philosophy. You put the processing hub in with the same idea as the pipeline. While we needed a commitment from Hess to proceed, the idea is that both the pipeline and the hub will eventually bring other subsea tiebacks onboard.
‘Also, the Gulfstar concept gives us an opportunity to lower engineering costs for other similarly sized discoveries in the Gulf, given that we already will have much of the work flows established.’
Simply put, its contribution today is important, but its future role could be essential. OE