Albacora Subsea Raw Water Injection Systems

Abstract

This paper presents the Albacora field Subsea Raw Water Injection (SRWI) systems. Application of SRWI involves some challenges, which demand a detailed and systematic analysis in order to evaluate the technical feasibility and establish the requirements to implement this solution. This paper describes the evaluation process carried out and details the adopted solutions. Furthermore, the system installation and operation are presented. The Albacora field is a mature field located at Campos Basin in water depths between 250 and 1100 meters. In order to increase the oil recovery, its reservoirs are requiring a significant amount of water injection, what was not considered in the initial phases of the Albacora field development project. Technical and economical constraints do not allow the use of conventional seawater injection plants, since current production units have no available area to implement a conventional water injection system. The selected alternative to overcome these constraints was the SRWI technology, by which seawater is injected in the reservoir with a minimum treatment, using mainly pieces of equipment installed at seabed. The feasibility analysis involved studies of the seawater compatibility with the reservoir rock and fluids, microbiological control, corrosion, etc. The solution was specified based on these studies and included subsea pumps, back-flushing filters, well components and topside facilities. In order to achieve required seawater flow rates, the adopted solution considered the use of three subsea injection systems, injecting around 16,500 m3/day in seven wells. Waterflooding is still the most common method used worldwide for improving oil recovery. The SRWI technology can be an important alternative to inject seawater where it is not possible to use conventional systems, mainly in mature fields. The SRWI is expected to generate large economical and technical benefits to the Albacora project. Introduction Water injection has a high economical impact in offshore projects, because it affects directly the recovery factor and the production flow rates. Hence, the development of technologies that overcome technical or economical problems to guarantee adequate water injection flow rates in offshore fields is critical. In some offshore fields, mainly mature fields, the impact of the conventional technologies in the topside facilities can be a constraint to increase or enable seawater injection. These conventional systems require the installation of too many pieces of equipment at the production units, demanding large areas that sometimes are not available. Other restrictions could occur, like load limitations, FPSO swivel constraints etc. One alternative to overcome these problems is the Subsea Raw Water Injection (SRWI) technology, by which most of the system is installed at seabed and seawater is injected with minimum treatment, leading to a much lower impact in the topside facilities. The SRWI alternative involves technical challenges, such as: seawater compatibility with the reservoir rock and fluids, microbiological control, corrosion, water properties, reliability of the subsea equipment and power, which limit the use of this technology in some scenarios. PETROBRAS established a R&D project to evaluate and develop this technology, involving technical feasibility studies, evaluation of scenarios and preliminary specifications. During this project, Albacora field reservoir studies indicated the need of large amounts of water injection and SRWI became the only economically feasible alternative identified to address this demand.

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