The Veslefrikk field is located in block 30/3 of the Norwegian sector of the North Sea. The field has now been on production for approximately ten years, and can be described as being in the decline phase. The Brent and IDS zones contain different fluid systems, and are produced through several commingled wells. Seawater is injected for pressure support. The first water breakthrough occurred in 1992. Although the ion composition of the Veslefrikk formation waters are not extreme when compared to other North Sea formation waters, severe scale formation has been observed. Both CaCO3 and BaSO4 scale have been identified. This is probably due to high reservoir temperature, 125°C (CaCO3), and the commingled production (BaSO4). Based on the field experience a preventive scale control strategy has been implemented. Scale inhibitor squeezes, re-perforation and mechanical and chemical scale removal are applied to maintain the productivity in the wells. Recently the effect of scale formation upon the production rates and cash flow, has been assessed. Two different scenarios, ‘No scale control’, and ‘No scale’, have been studied. These cases have been compared to the baseline production profile. This consists of the historical production data and the base case prognosis for the field, which includes scale control at today's level. The work, covering the period from start of production to June 1999, shows that 9 million Sm3 less oil would have been produced if no scale control had been implemented. This represents a value of approximately 1100 million USD. The cost of the scale control operations which have been performed, including inhibitor squeezes, reperforations and mechanical and chemical well stimulations, are approximately 6.3 million USD. 3.7 million Sm3 more oil, representing a value of 400 million USD, could have been produced if the field had not experienced any scale formation. Assuming constant reserves, the accelerated production represent a 320 million USD increase in the total field lifetime NPV. In addition, the operating costs would have been reduced. The results clearly show that scale control operations are highly beneficial, and it is recommend to intensify the preventive scale control at Veslefrikk.

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