Effective Treatment of Subsea Wells with a Solid Scale Inhibitor System

Abstract Aqueous based scale inhibitor squeeze treatments have been routinely deployed on Total Oil Marine’s North Alwyn field for many years. More recently, declining reservoir pressure in parts of the field, coupled to poor reservoir communication has led to a considerable increase in the time required to bring treated wells back onto production. On subsea well 3/4a-15s, it was anticipated that extended shut-in periods would be required to allow sufficient pressure build up for production restart following a platform squeeze. To minimise deferred oil cost associated with scale inhibitor treatments an alternative deployment technique has been applied to treat subsea wells such as 3/4a-15s on North Alwyn. A weighted solid scale inhibitor capsule, suspended in a carrier brine has been pumped to the wellhead and allowed to fall, under gravity into the sump. On reaching the sump, the diffusion of scale inhibitor from the capsule established a concentration gradient, which delivered a near constant level of inhibitor over the lifetime of the treatment. The subsea well on North Alwyn treated using this technique returned to production in less than 24 hours. In addition, the encapsulated inhibitor treatments have out-performed previous squeeze treatments, protecting a large volume of water to the minimum inhibitor concentration (MIC). This paper will describe the concept of the delivery system, details of the treatments and present the return profiles.