SEA WATER LIFT PUMPS

Sea water lift pumps Literature review

Sea water lift pumps Literature review

North Sea operators are risking more ambitious subsea step-outs. Oil from TotalFinaElf's Otter field will be driven 23 km (including well length) to the Eider platform via downhole electric submersible pumps (ESPs). This is a significant increase on the previous distance record for subsea ESPs in the North Sea, the 14 km between Gannet E and the Gannet A platform.

However, TotalFinaElf views its scheme as a standard-bearer for future developments, rather than a gamble. Dual ESPs - a world first - are being fitted in each of Otter's three production wells to provide backup and minimize workover interventions. The project will also extend the service life of Shell's Eider platform, which otherwise faced permanent shutdown in 2004/5.

Phillips discovered Otter, formerly known as Wendy, in 1977 in UK northern North Sea block 210/15a, in 182 m of water. Petrofina acquired the undeveloped field and surrounding acreage in 1994, when it was seeking a new role as a production operator (Klivington, et al., 2004). It drilled a successful appraisal well in 1995 and launched development studies the following year, entru-sted to Offshore Design Engineering. Among the concepts screened were a stand-alone FPSO loading facility and subsea wells tied back to a third-party platform.

No natural drive

The field is a mid-Jurassic accumulation lying at a depth of 2,000 m in Brent sandstone formations. Although the crude is good quality, the reservoir lacks natural drive, with relatively little associated gas. Importing lift gas was considered initially, the problem being how to do so economically and efficiently with supplier fields all more than 20 km distant. Planning was then stalled, first by low oil prices in 1998, and later by the asset review resulting from the merger with Total and Elf. However, Otter was considered worth retaining as potential feedstock for the Sullom Voe terminal on Shetland, of which TotalFinaElf Exploration UK PLC had a 9% interest.

"There was a renewed determination to use the full technical know-how of the combined group to get this project moving," says Jacques Azibert, Northern North Sea asset manager for TotalFinaElf. "The challenge was how to make the development economic using new technologies, and also how to make use of the nearby infrastructure." (Jeremy, 2002)

All the earlier provisional schemes were based on three producer wells and two injectors with full reservoir voidage, and this principle was retained. One new idea was to accelerate production to enhance the project's economics. TotalFinaElf now inclined toward a subsea development, although options for the host platform had narrowed, with capacity on BP's Magnus being complicated by a new scheme to enhance oil recovery through gas piped from the Foinaven field.

Alternative drive

Thinking then veered toward use of ESPs as an alternative drive mechanism to gas, powered remotely by individual electrical cables. "Total already had experience with ESPs in the Middle East, while Elf had used them off West Africa," says Jacques Azibert, Northern North Sea asset manager for ...