Precipitation of mineral scales causes many problems in oil and gas production operations: formation damage, production losses, increased workovers in both producers and injectors, poor injection water quality and equipment failures due to under-deposit corrosion. The most common mineral scales encountered with downhole and topside processes are sulphate and carbonate-based minerals. The development over the past few years of fields where high temperature and high salinity brines are being produced with associated hydrocarbon has presented a more challenging environment for scale management. In such fields hydrogen sulphide gas is quite a common component of the produced fluids. To remove the gas from the process stream hydrogen sulphide scavengers are applied. The introduction of these chemicals can result in a secondary problem arising from their relatively high pH. Changes in localized pH associated with the introduction of such production chemicals has been observed to induce carbonate scale precipitation and in the case of one high salinity brine system unexpected sulphide scales of lead and zinc.
This paper will focus on the mechanism of occurrence of such scale types within a North Sea field and how an inhibitor package was developed that controls both carbonate and sulphide scale formation while it also effectively controls associated hydrogen sulphide. It will outline the field and laboratory testing methods utilized for assessment of the scale challenge, the chemical screening methods used and assess the currently available prediction software so that evaluation of the potential problem within fields during appraisal can be determined prior to production commencing.