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.
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.