Abstract

Gullfaks has been in production since 1986 and produces approximately 11 500 Sm3/d oil from three Condeep platforms. The average water cut is approximately 75 to 80% and GOR of approximately 200 Sm3/Sm3. It has been estimated that between 50 to 100 tonnes of sand is produced yearly per platform with approximately 60 to 70% of the wells in active production (around 90) are limited by sand production. The typically well completion is cased hole with selective production through perforated liners. Rock mechanics studies have shown that sand will be produced irrespective of well inclination and perforation design.

On Gullfaks, the sand management strategy used has been to produce wells at "maximum" or "acceptable" sand rates. This strategy has led to significant gains in production although there are challenges with this approach that include choke erosion, sand removal from the separators and oil in water quality associated with discharge to sea. In response to this, Statoil have investigated different methods of retaining sand downhole by chemical sand consolidation, of which in situ calcium carbonate precipitation will form the basis for the paper. This technology involves squeezing into the near wellbore predefined concentrations of urea and calcium nitrate along with the enzyme urease. After application, the well is shut in during which the enzyme catalyses the decomposition of urea to bicarbonate that reacts with calcium to form calcium carbonate.

The paper will provide details of the laboratory evaluation and, in particular, focus on the field results from the first ever application of this type. A low risk candidate well was selected that had a short perforated interval (19 m) and produced 88 Sm3/d oil with a water cut of 94 %. Results will be presented of the operation design and planning, logistics examination, thorough risk evaluation, and post-operation results with lessons learned.

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