The Heidrun Field, located on the Haltenbanken area, is one of the major fields which came on stream in the Norwegian Sea since 1995. At peak production the field is capable of producing 38,000 m3 of oil and 6 MSCM gas per day. It also takes in 22,000 m3 of injection water each day. The field is characterised by the large clay content in its three formation sands Fangst, Tilje and Are. Most of the producing wells are installed with gravel pack or screens due to poor sand consolidation. The reservoir has a bottom hole temperature of 85 °C and a relatively low reservoir pressure of 250 bar, hence seawater injection for pressure support is needed. With Ba++ level ranging between 180 to 700ppm in the different formations, the potential for downhole sulphate scale deposition within both the formation and the gravel pack, after seawater breakthrough is extremely high. A scale control strategy based on preventive squeeze treatment is therefore desirable to minimise any formation damage caused by such deposition.

However, two treatments using water based scale inhibitor carried out prior to 2000 had caused significant process problems during back flow. Severe emulsion problems were experienced, resulting in process upset and poor water quality. The low reservoir pressure meant that long clean up periods were needed with much deferred oil production. Such undesirable side effects make the operator less willing to take preventive action. Over the past 6 months, with the availability of an oil based scale inhibitor and a new ‘biodegradable, green’ water based product, we have successfully treated a number of oil producers with a wide range of water cut. In all cases, there was minimum process upsets on flow back and resumption of oil production shortly after. In the case with the ‘green’ product, it is most encouraging since this is the FIRST North Sea application and the chemical offers a high degree of biodegradability. This contributes significantly to the step improvement on the environmental impact when the return of a large peak of unwanted chemical is often associated with a traditional water based squeeze. In this paper we shall describe the processes of selection, evaluation, design, implementation and follow up of these new treatments. Based on these results, we have now established a treatment strategy which can be applied to wells producing from the different formations and with various water cut.

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