In 1998 the Norwegian Government issued a White Paper (1) requiring the oil industry in the Norwegian sector of the North Sea to develop a strategy of reaching "zero discharges" of produced water within 2005. Operationally, zero discharge has since been defined as "zero harmful discharge" (2). In order to quantify the "harmfulness" of these components, a management tool, the EIF (Environmental Impact Factor), has been developed (3,4,5).

ConocoPhillips originally projected to achieve a combined 95 % reduction in EIF at Ekofisk by introducing Produced Water Re-injection (PWRI). However, after a pilot PWRI test was performed, the conclusion was that re-injection was not cost efficient and most importantly, it became apparent that it introduced a risk of reservoir souring, and could also cause substantial loss of oil produced.

It was then decided to evaluate best available produced water cleaning technologies (7,8,9). Based on previous test data, the results showed that Solvent Extraction (CTour) was the most promising technology for removal of dispersed oil and dissolved aromatic components. Pilot tests of CTour were conducted in 2004-05, and the results showed an 80% EIF reduction, reaching residual oil of <2 mg/l and Naphtalenes and PAH reduction by 80-95%. The CTour Process was successfully scaled up to 300 000 BWPD full field installation, and was started up and commissioned 4'Th quarter 2007. The results from performance testing indicate that the efficiency from the original pilot tests had been successfully reproduced, yielding residual OiW of 1-2 ppm and Naphtalenes and PAH reduction by 86-92%.

It is further concluded that the process yield residual discharge reduction in accordance to the guaranty parameters originally issued upon signing of the licence agreement.

The CTour Process is generally based on using available condensate from suction scrubbers as solvent, but at Ekofisk, NGL is used as extraction fluid.

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