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Choosing a Seawater Sulfate Removal Alternative

SRP systems from Veolia Water Solutions & Technologies today account for approximately 40 percent of the world's seawater sulfate removal capacity.

SRP system supplied to MODEC

MODEC Offshore Production Systems has awarded a contract to Veolia Water Solutions & Technologies for their PSVM FPSO project for the BP Angola PSVM (Plutão, Saturno, Vênus and Marte) field development in Block 31 Angola. The award is for the supply of a seawater treatment system comprised of pretreatment, vacuum deaeration and sulphate removal package (SRP) systems with a capacity of 31,800 m3/day (200,000 BWPD). Also included within the scope is an integrated seawater reverse osmosis (SWRO) system for process washwater sized at 20,000 BWPD.

Avoiding Scale

The SRP is designed to remove sulphates and other divalent ions from injection water to enhance oil recovery using Dow/Filmtec SR90 membranes. The removal of these ions reduces the tendency of barium sulphates and strontium sulphate scale to form in the reservoir. The wash water is used in the crude oil desalting process.

"This is the first SRP project to be awarded to VWS by MODEC, and can be attributed, in some manner, to the success of our previous SRP for BP, the FPSO Greater Plutonio, also located in Angola (Block 18), completed in 2005," says Brian Baillie, Sales Manager for Veolia Water Solutions & Technologies. "That installation remains the world's largest capacity SRP."

Veolia SRP systems today account for approximately 40 percent of the world's seawater sulphate removal capacity.

Providing A Complete Barrier

offshore water treatment Veolia Water Solutions & Technologies

The sulphate removal process removes sulphates and other divalent ions from the injection seawater to enhance oil recovery.

The sulphate removal process uses a membrane-based system that removes sulphates and other divalent ions from the injection seawater to prevent the formation of barium sulphate and strontium sulphate scale in the subsea injection piping system and in the reservoir itself.

Problems with Alternatives

"Barium and strontium sulphate scales are notoriously difficult to remove because they cannot be easily dissolved," Baillie says. "Squeeze inhibition treatments are often utilized to improve the well permeability, but these are extremely difficult to control and cannot be applied to complex sub-sea networks or from floating production storage and off-loading vessels (FPSO). Where pipeline scaling is experienced, this has to be removed by mechanical means."

Sulphate removal is accepted in the industry as an effective and cost-efficient alternative to these other approaches, Baillie says, especially in oil developments where chemical injection of well workover is problematic and/or expensive.

"A further benefit of removing sulphate in the injection water is the prevention of well souring by contorolling sulphate reducing bacteria (SRB). This reduces both equipment corrosion problems and the equipment required for scrubbing, removal, and handling of hydrogen sulphide."

Benefits of Sulphate Removal Reduces seawater ion concentration from around 2,500 ppm to less than 50 ppm (at temperatures of < 24ºC) Significantly reduces sulphate scale precipitation in production wells Reduces or eliminates scale inhibitor squeeze treatments Eliminates economic and operational impacts resulting from scaling in reservoir Increases productivity index by limiting pipe constriction due to scaling Assists in maintaining reservoir permeability by limiting formation plugging caused by scaling Prevents well souring by controlling sulphate reducing bacteria (SRB) which in turn reduces equipment corrosion problems and the equipment required for scrubbing, removal, and handling of hydrogen sulphide Reduces safety hazards associated with hydrogen sulphide Has an additional safety benefit by reducing scale and thus the potential of naturally occurring radioactive material which can be attached to the scale Meets the stringent design and environmental criteria related to offshore platform

Contact: Brian Baillie
mailto:brian.baillie@veoliawater.com
+44 (0) 135558 8015