Albacora Subsea Raw-Water Injection

Abstract

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper OTC 24167, ’Albacora Subsea Raw-Water-Injection Systems,’ by L. Buk Jr., C.A. Andrade, J.B. Azevedo, E.J.J. Coelho, O.C. Costa, C. Kuchpil, A.G. Siqueira, and A.L.S. Souza, Petrobras, prepared for the 2013 Offshore Technology Conference, Houston, 6-9 May. The paper has not been peer reviewed. To increase the oil recovery in the Albacora field, significant water injection is required that was not considered in the initial project-development phases. Technical and economic constraints do not allow the use of conventional seawater-injection plants because current production units have no area available to implement a conventional water-injection system. Application of subsea raw-water-injection (SRWI) systems in the field involved challenges that required a detailed and systematic analysis to evaluate the technical feasibility and establish requirements for implementation. This alternative enabled seawater to be injected into the reservoir with minimum treatment by use of equipment installed on the seabed. Introduction In some offshore fields, mainly mature fields, the addition of conventional technologies to topside facilities can constrain the use of seawater injection. Conventional systems require the installation of too many pieces of equipment at the production units, which requires large areas that sometimes are not available. Other restrictions include swivel constraints on floating production, storage, and offloading vessels (FPSOs) and load limitations. One alternative is SRWI technology in which most of the system is installed at the seabed and seawater is injected with minimum treatment. This system has minimal effect on the topside- facilities footprint. The SRWI alternative involves technical challenges that include 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 project to evaluate and develop this technology, involving technical-feasibility studies and evaluation of various scenarios and preliminary specifications. During this project, Albacora-field reservoir studies indicated the need for large amounts of water injection, and SRWI became the only economically feasible alternative identified to address this demand. Albacora Field Albacora is a giant field in the Campos basin, approximately 100 km offshore Brazil, covering an area of approximately 235 km2, with water depths of 250 to 1100 m. The field was discovered in September 1984 and has an estimated oil-in-place volume of 4.4 billion bbl. Pilot-phase production started in 1987 with the FPSO P.P. Moraes. In 1993, a second development phase started with the semisubmersible P-24, which was replaced later by the definitive production system with two production units: the semisubmersible P-25 and the FPSO P-31, installed in 1996 and 1998, respectively. Field oil production peaked in 1999.