For BP's Eugene Hughes, designing for minimum appraisal was another crucial consideration in deepest West Africa. "Like anyone else, we're trying to go to fast-track developments. These days if you want money from the BP board, you have to get your oil out quicker. If you ask them for four years, they'll give you three. We used to think five years was good."
Hughes added that "in my view, appraisal doesn't do much good. I haven't seen a project where the production matched what the reservoir people predicted. They change things during the design anyway. In deepwater, the big costs are drilling. Drilling takes up 41% of the cost of a 500MM bbl field, and 39% of a 1,000MM bbl field. Don't spend too much on drilling and then end up constraining your final flow."
Hughes advised his audience to look at the implications of pre-ordering topside plant. Associated gas seems unavoidable in the West African deepwater, and lead times for gas plant are long. But rather than budget for 500GOR plant for what looks to be a 500MM bbl oilfield, he said, take a risk and invest in 1,500 or even 3,000 GOR plant. This could cut the time from discovery to first oil to three to three and a half years.
The argument is based on big new reserves coming to light some time into the production phase. Initially, he argued, the development may lose a little on its rate of return, but long term it would make money, with minimal outlay on appraisal. This would be preferable to undersized gas plant constraining oil production, which would cut the rate of return dramatically.
Hughes endorsed research into riser base injection systems, stating that slug formation was already a problem around the Foinaven risers west of the Shetlands. "We think this problem will be compounded in the significantly deeper waters off West Africa." BP studied injection for its latest Shetland project, Schiehallion, but this was turned down owing to the expense. Another cost dilemma Hughes identified related to trenching and burying of flowlines at very great depths.
The limited market for associated gas in West Africa could prove a serious barrier to deepwater developments. If flaring were banned, said Delaittre, "an oil project may not be profitable". Hughes said that BP was investigating LNG on an FPSO. "The problem is cryogenic transfer offshore. We still have the same loading solutions that were offered 10 years ago." Shell's Don Henery added that cryogenic lines don't normally take well to a steel FPSO, which advances the case for concrete. But concrete might also limit storage.
Petrobras' Roberto Alfradique Vieira de Macedo countered that in Brazil, "not to have gas is a problem. We have very few non-associated gasfields, so we're having to build a new pipeline overland from Bolivia at a cost of $2 billion. If we had associated gas, it would be a very good solution for us."
Petrobras' aim, he said was to produce 1.65MM b/d in 2005, twice its current production, which means developing more and ever-deeper fields. The company has drilled 199 wells in waters of 400 meters and beyond, way ahead of Shell with 86. Last month, he added, it was due to break its own record for subsea completion, reaching 1,100m on East Albacora using a 9 km electric cable and a subsea transformer placed close to the tree.
According to da Macedo, "our vision for ultra-deepwater will be a few high productivity subsea wells connected to subsea manifolds and subsea boosters. These will send production to FPSOs in 1-1,500m of water through flexibles or steel pipes. Oil will be offloaded to tankers, with any gas compressed for reinjection or piped ashore."
Henery said that deepwater oil reserves off West Africa tend to be in shallower depths below the seabed, militating in favor of mini-TLPs or subsea wells. Da Macedo replied that within Petrobras, there were conservatives who favored FPSOs and were afraid of trying TLPs. The directors had blocked a move to put a TLP on the South Marlim Field.
As production goes deeper still off Brazil, Petrobras is implementing a new mooring spread, revealed da Macedo, to achieve higher compliance on the FPU's stern, resulting in a partially weathervaning system. "We are also looking at extended reach wells for ultra deep waters."
Copyright 1997 Oil & Gas Journal. All Rights Reserved.