Abstract

Waterflooding with seawater is the most common approach to supporting reservoir pressure and stimulating oil production in offshore installations. However, producing wells can be significantly damaged when seawater breakthrough occurs, as BaSO4 scale can deposit in the near wellbore area; especially for wells with formation waters containing a high concentration of barium ions.

Different ion monitoring and analysis methods are traditionally used to calculate the percentage of seawater breakthrough, with varying levels of accuracy and reliability. This presents a significant challenge, as accurate determination of seawater breakthrough, especially at its onset, is critical for scale management and selection of appropriate mitigation strategies.

This paper discusses the development of a simple methodology for seawater breakthrough determination in a North Sea field, using reactive ions. Unlike other approaches, the method calculates the percentage of seawater breakthrough through the balancing of the seawater breakthrough as determined from individual reactive ions; it also allows the determination of BaSO4 mass deposition downhole, corresponding BaSO4 mass stripped in the deep reservoir and amount deposited in the near wellbore.

The relationship between oil production rate and percentage of actual seawater breakthrough has been correlated based on matching well historical data. The different stages of formation damage as a function of increasing seawater breakthrough are also presented. Last, the difference between the contribution of BaSO4 stripped in deep reservoir and deposited in the near wellbore on and its impact on formation damage is discussed.

This paper presents a comprehensive study of monitoring and calculating seawater breakthrough using a robust and accurate methodology. Seawater breakthrough and the relationship between downhole scale deposition and formation damage have been correlated using real field data. Combined with scale predictions, it is proposed that this approach can enhance scale management strategies and thus optimise oil production. The method is applicable to any oilfield using seawater flooding, rendering it a significant tool in optimising oil production and minimising well downtime.

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