VWS Westgarth has been awarded a multi-million dollar contract by SBM Atlantia for of a seawater sulphate-reduction package (SRP), using Dow FilmTec membranes, in a Brazilian offshore oil and gas field.
The award is for the design, supply and delivery of a single-lift module seawater SRP system with a capacity of 20,060 m³/d for the Baleia Azul field, Campos Basin, offshore Espirito Santo state, Brazil.
The SRP is designed to remove sulphates and other divalent ions from injection water to enhance oil recovery using Dow Filmtec membranes. The removal of these ions reduces the tendency of barium sulphate and strontium sulphate scale to form in the reservoir.
This new award will be the first collaboration by VWS Westgarth, part of Veolia Water Solutions & Technologies, with SBM Atlantia and can be partly attributed to the success of previous SRP projects executed for SBM Inc of Monaco and SBM Gusto MSC of Holland.
Barium and strontium sulphate scales are notoriously difficult to remove since they cannot be easily dissolved. Squeeze-inhibition treatments are often used to improve the well permeability, but these are extremely difficult to control and cannot be applied to complex subsea networks or from floating production storage and offloading vessels. Where pipeline scaling is experienced, this has to be removed by mechanical means.
The installation of an SRP, to extract the sulphates from the seawater prior to injection, is often seen as a most economical alternative approach. The SRP uses nanofiltration membranes (FilmTec™ brand SR-90 membrane elements) to remove the sulphates while leaving the other salts (sodium, chloride etc) substantially unaffected, thus maintaining the stability and permeability of the formation clays. The Marathon Oil Company, using membranes supplied by Dow Chemical Company, invented the process.
The membranes are typically configured in a SRP with a “2-array, brine staged” arrangement. With this arrangement, the seawater feed is introduced to the first array of membranes, which allows 50% of the feed to pass through the membrane material with the sulphate being rejected on the membrane surface.
The 50% reject water (or brine) is then fed to the second array of membranes, where again 50% passes through as low-sulphate water. The two flows of low-sulphate water are blended to give an overall recovery of 75% with the remaining 25% of increased sulphate reject being safely discharged overboard without endangering the environment.