New Test Method for Scale Inhibitor Qualification Verified by Field Testing

A new laboratory test method for qualification of scale inhibitors for carbonate, sulphate and sulphide scale has been demonstrated. The new method reflected conditions at the first stage separator at Gullfaks A in a more realistic way than by use of the more common dynamic tube blocking test. Results of this method have been compared with dynamic tube blocking and static scale inhibition tests and a full-scale field test. The method developed includes iron particles, realistic H2S and CO2 pressures under anaerobic conditions allowing water chemistry similar to field conditions. The method can be utilised for water with carbonate or sulphate scale potential or a mix. A pH closer to system conditions and scaling on surfaces can be achieved without adjustment of the water composition. The residence time can be up to 5 minutes, which typically represent the residence time in for example separators. The results are interpreted through visual observations through glass coils and Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM/EDS) analyses of steel coils. Using the new method, significant scale was formed when the incumbent scale inhibitor was tested which was also observed in the field. Several alternative scale inhibitor chemistries were recommended for evaluation based on environmental properties, field experience and cost efficiency. When testing the chemistries with the new method only one inhibitor gave acceptable results (no scaling nor co-precipitation of scale and scale inhibitor). This inhibitor was recommended for further testing in a two-week field test. The field test included quantification of suspended solids and a filter rig test. The results from the field test confirmed the laboratory results showing that the selected inhibitor was more efficient than the incumbent.