This paper documents the performance of different sand control completion types in three subsea fields tied back to the Statfjord C platform. Seawater is injected as part of the reservoir drainage strategy on all three fields and this presents challenges related to precipitation of sulphate scales when the seawater mixes with incompatible formation water in the near wellbore area.

Well completions are of various types on these fields; conventional perforated casing with normal and orientated perforated phasing, sand screen, cased hole and openhole gravelpack. This basket of different completion solutions reflects the differing sanding tendencies of the various reservoirs and the general developments in completion technology throughout the field life. Sulphate scale buildup in the screen and near well bore has been found to be a major damage mechanism in all sand control completion types. The wells typically show immediate productivity index (PI) reduction following seawater breakthrough. Some data verify a stabilization of PI when the seawater cut reaches a high level. A comparison of the differing scaling tendencies of the completion types is made and guidelines on developments in skin as a function of production characteristics are presented.

Up to 1995 cased hole gravelpack was the dominating sand control technique in Statoil but poor trends in productivity following water breakthrough has lead Statoil to adopt openhole solutions. Theoretical arguments suggest that openhole completions are more tolerant of scale than cased hole gravelpacks. This paper documents whether any significant differences in scaling tolerance have been experienced in these fields. This has had consequences for estimation of productivity development and the expected scale prevention strategy chosen for the Statfjord depressurization project.

The paper shows that combined scale dissolver and scale inhibitor treatments have been successful in regaining productivity in these. Bullheading of scale treatments down the methanol service line has been a very cost effective method of treating scale depositions in wells tied back to the platform with distances of up to 7 km. For templates further from the platform, treatments are now performed from a dynamically positioned boat where a flexible hose is connected to the choke bridge.

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