As offshore oil fields are being developed towards deeper and deeper waters, new technologies are required to curb capital expenditures.
In Brazil, where oil consumption is increasing and huge oil fields lie in high water depths, the issue is particularly pressing. Earlier and higher oil production from those oil fields could be attained by the use of Electrical Submersible Pumps (ESP), so far restricted to dry completions. Also longer distances from well to platform would be made practical.
For the initial phase of this development, Petrobras worked together with Tronic, Reda, Piralli, Lasalle, Sade- Vigesa and Cooper.
As a result, first-in-the-world ESP installation in a subsea well has been successfully achieved on October/f 994 in RJS-221, located at Carapaba Field, Campos Basin, Brazil.
The development of deep water oil fields in Brazil has been leading to the use of floating production systems linked to subsea central manifolds and to satellite wells.
Oil flow from subsea wells is driven by natural reservoir pressure aided by gas lift injection, whenever necessary, as no other artificial lift method was available for subsea production.
For each field, well-to-platform distances are limited to the reach of reservoir pressures, which decline with depletion, requiring water injection. Gas lift is of little help for that matter, once it becomes less efficient as orizontal distanoes increase and BSW rises.
This scenario requires many deep water platforms to cover a large drainage area and renders uneconomical any distant reservoir that is not large enough to hold a new platform. A new method was needed, that by adding energy to produced fluids, would increase flow rates and thedistance from subsea wells to platforms., allowing for lower capital and operational costs and higher recovery factor.
In order to study alternative methods of artificial lift for subsea wells, a Project was created as part of the Technological Innovation Program for Deep and Ultra- Deep Water (PROCAP 2000) by the end of 1992.
After an evaluation of the available methods in the market, priority was given to the Electrical Submersible Pump (ESP) system as the most advanced and, at the same time well known and widely used lift method in dry completions.
The studies indicated that the equipment required for the installation of an electrical submersible pumping system in a subsea well could be made available in the short time. In fact, some components had already been laboratory tested. Some could be developed from existing technology.
In parallel, technical and cost feasibility studies have led to the identification of suitable scenarios for the application of this new technology, particularly the giant oil fields of Albaoora, Marlim and Barracuda. Figure 1 compares production rates of ESP with several different run lives against gas lift for a well in Albacora deep water field. The use of ESPS would allow for a higher production of oil.
Wells equipped with ESPS, however, require more frequent workover as opposed to gas lift wells, implying in higher production costs, specially in deep waters.