The Varg field (PL038, Block 15/12) is located in the Norwegian Sea. The Varg reservoir is Oxfordian sandstone of Jurassic age, with an upper (1000-2000 mD) and lower (100-200 mD) sand separated by a mud rich sandstone. The field is highly compartmentalized and is located around a salt dome, and contains a number of different formation waters ranging from high salinity, higher barium (up to 280 mg/l) in the West and lower salinity and lower barium (30 mg/l) in other areas. All waters contain naturally occurring dissolved iron at concentrations up to 175 mg/l. Following scaling in several wells, a chemical re-selection and treatment optimisation programme was initiated. Extensive laboratory studies were undertaken to select optimum inhibitors, which was further complicated by environmental requirements. The presence of dissolved iron was shown to have an adverse effect on the incumbent scale inhibitor, leading to the selection of a number of alternative products. Given the highly compartmentalized nature of the reservoir and the large permeability contrast between zones, near wellbore modelling studies, examining chemical placement using both conventional (aqueous) based treatments and also viscosified treatments, were conducted. The potential for poor placement and subsequent poor lifetimes led to further detailed simulation work using up to date PLT logs to further refine the treatments in subsequent wells. Therefore, this paper describes the various challenges facing scale control in the Varg field. The paper presents results from a chemical re-selection exercise showing the controlling influence of dissolved iron, together with coreflood studies used to select the most effective non-damaging product for subsequent field trials. Extensive near wellbore modelling results are presented to illustrate the challenges faced with respect to effective chemical placement, which highlight the challenges faced. Several field trials have now been conducted with a new chemical and the results of these are also discussed.

You can access this article if you purchase or spend a download.