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Deepwater Challenges (From Hart's E&P)

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An explosion of potential deepwater developments looms on the horizon.

Surface facilities and subsea tiebacks in the Gulf of Mexico, offshore West Africa and Brazil could triple the number of producing fields in a short time. However, several obstacles must be overcome for the near-term potential of deepwater development to materialize.

Deepwater platforms

During the next 5 years, a threefold growth is expected in deepwater platform prospects. Twenty-four production platforms exist in water depths greater than 1,641 ft (500 m), but during the next 5 years, 66 potential deepwater platform installations are expected. Considering the regional distribution of these new units, 27 floating production systems are identified for the Gulf of Mexico, including 14 spars. No floating production, storage and offloading vessels (FPSOs) are foreseen for this region, but extensive environmental impact and risk-assessment studies relating to their deployment have been completed. Elsewhere are nine identified FPSO projects off Brazil and 11 envisaged off West Africa. The use of semisubmersibles and tension-leg platforms (TLPs) is also set to expand, most notably with seven semisubmersibles possible off Brazil and nine more TLPs for the Gulf of Mexico. However, perhaps the most remarkable trend emerging from Infield Systems' data is the significant growth in the use of spar-based production platforms, with 19 new units on screen for the period to 2005.

The challenges ahead

As water depths increase, so do drilling and completion costs, and considerable efforts are under way to constrain these. The ultimate objective must be to maximize well productivity and enable a reduction in well numbers. Techniques such as large-bore completions, multilateral and highly deviated wells and "smart" wells offer great prospects. Surveys of oil company research and development interests show deepwater flow assurance as a major area of Concern.

Problems range from developing low-pressure reservoirs to flowline-blocking hydrate fornation. Few oil flow lines exceed 12 miles (20 km), although 62-mile (100-km) and longer gas flow lines exist in the Gulf of Mexico. The prize for increasing flow distances is huge and has been much discussed. In situations such as off West Africa, low reservoir energy limits flow distances significanthy, articularly when oil has to be raised to surface through great water depths.

Alternatives are under development, and initial trials include subsea separation, multiphase pumping and downhole pumps. However, most of these subsea solutions require large amounts of electrical energy to be transmitted to the wellhead. The industry view seems to be that in practice, conventional subsea transmission is linited to about 19 mil.es (30 km).

Work by Shell suggests TLPs may have a practical limit of a 4,922-ft (1,500-m) water depth. For the ultradeep, it seems the future will see continued use of the tried and tested FPSO and semisubmersible solutions, although new floating concepts are under discussion.

    

Concerns about the intervention costs for subsea-completed wells have arisen, particularly in remote areas where intervention facilities are not readily available. An area of major interest is the use of "dry," surface-based well completions on platforms rather than using subsea wells. This dry wellhead capability is one of the major drivers behind the significant interest in the spar concept. According to the Infield database, 19 spars are being considered for deepwater field developments through to 2005. Four of these units are intended for the West African region, one for Brazil and the remaining 14 for the Gulf.

Chevron recently raised a few eyebrows by selecting a 42-slot compliant tower concept for its development of the Benguela-Belize- Tomboco field complex on Block 14 off Angola in water depths of 1,312 ft to 1,641 ft (400 m to 500 m). This had been expected to feature an FPSO-led subsea scenario. It has been 3 years since the last application of the coiled tubing (CT) solution, and interestingly this was on Chevron's new partner Texaco's Petronius project in 1,772-ft (540-m) waters in the Gulf of Mexico. This was Texaco's first deepwater project, and the CT was installed in late 1998. It carne onstream in May 2000, a year behind schedule after one of the deck modules was dropped and sank during installation.

Resource shortages

The rationalization of human resources following the last oil price downturn has forced projects to be put on hold as some oil companies are without sufficient project managers to initiate all field developments in their corporate portfolios. Contractors also have the same problems -and are repo1ting unprecedented shortages of people and equipment.

The other potential problem is offshore vessels. The average age of the offshore vessel fleet is 20 years, and nearly 30% of the global fleet (1,013 vessels) is more than 25 years old. One result is that much of the existing fleet probably has a fairly limited economic lifetime and is not well suited to deepwater and subsea operations.

A shortage of experience?

Although deep water represents only a small part of global offshore activity, it is without doubt the technological leading edge, and the future prospects are considerable. The Campos Basin is stated by Petrobras to extend down to 11,155ft (3,400 m), and off West Africa, seismic companies have reported "interesting" seismic returns from 13, 124-ft (4,000-m) waters. A new drilling record was established May 2, when the Discoverer Spirit spudded in nearly 9,678 ft (3,000-m) waters in tile Gulf of Mexico, but the production record at 6,080 ft (1,853 m) is a long way off. E&P

For Data sources used please contact Infield

This article was published in 2001. We track developments Offshore on a regular basis and produce market reports covering all the sectors. Click here for more information or upto date listings of our articles.

  
     
 
   
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