This paper is based on work performed for Deepstar CTR11901 (for more information on the program see www.deepstar.org).
On average, only a third of in-place oil is recovered in Miocene reservoirs in the Gulf of Mexico. Water injection has been used to enhance the oil recoveries with limited success. Low salinity water injection could potentially further increase the oil recoveries achievable through seawater injection.
For deepwater oil fields and those requiring long tie-backs to the existing host processing platforms, local subsea processing systems providing low salinity water injection could be useful in improving development economics.
A Deepstar study has been carried out to evaluate the existing technologies for such subsea processing system to generate the low salinity from the seawater at 10,000 feet of water depth. Several conceptual process schemes have been defined and evaluated, employing various combinations of technologies, and compared from the point of view of operability, maintainability and technology maturity level. Technology gaps have been identified in the selected technologies and roadmaps have been defined to fill those gaps.
The paper describes the methodology that has been used to review the existing technologies for water treatment and evaluate their potential for subsea application, presents the main results of the state of the art review and gives an overview of four process schemes defined for subsea implementation of a low salinity water injection station. Whole range of technologies for water desalination have been studied including membranes, electro-dialysis and the use of hydrate formation. The defined schemes combine desalination with other function technologies in order to optimize the make-up of the low salinity water to meet the particular reservoir needs.