Gel is considered to have an interesting potential for water shut off applications, especially in fields having natural shale barriers and large permeability variations and/ or where reduction in tubing/ casing diameter is not wanted. This paper describes a case study from the Statfjord Field where polymer silicate gel was used to build up experience for water shut off applications of the lower producing interval in a well that produced from two intervals. The intervals where separated by 5m in 9 5/8" casing and located at approximately 3100 m.

The primary objective was to shut off water and secondly to evaluate gel technolog)'. Mechanical techniques and gel technology were considered as means of achieving the objectives. Both required the use of 2" coiled tubing in a live well (Fig. 14). Gel technolog)' was selected since diameter restriction in the casing was not wanted due to potential later perforations deeper into the well combined with desire of qualifying the technolog)' and related techniques.

This paper reports some of the results achieved in the laboratory, and give references to papers where the laboratory techniques and results are given, refs. 1 through 5. The pre planning and the laboratory' testing for finding a suitable gel formulation was also performed in collaboration with a service company.

Therefore this paper focuses mostly on the well performance, placement of plugs in the well by wireline and coiled tubing, pumping of the gel solution through the coiled tubing and into the lower perforation interval and evaluation of results.

The operation has been an economical success. After water isolation from the lower interv al, the well has produced oil with a gross value of 15 mill. U.S.$ in 6 months and the operation had a pay back time of 50 days.

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