Production drop caused by down hole scale deposition is becoming a serious problem not only in wells producing with high water cut but also in deep, hot, sour gas wells with very low water cuts(trace to 6%).

This paper presents a case study of CaCO3 & CaSO4 scale deposition in a sour well in north of Pakistan that resulted in substantial production drop. HCl (15%) was used to dissolve/wash the scale obstruction in the tubular and clean the perforation of well. Although the treatment was successful in dissolving the scale and restoring the production, yet these production gains were lost rapidly. Scale dissolver treatments followed by scale inhibitions were also implemented but no appreciable results were achieved. A detailed in house study was carried out by POL for scale analysis and its removal techniques. Scale monitoring by produced water analysis, gauge cutter runs, production & WHFP fluctuations, gas analysis and review of seven scale cleaning jobs guided to carry out organic scale dissolving job.

It was concluded that 15% HCl acid pumped to dissolve the scale precipitate out due to increase in PH and Bi Carbonate decomposition caused by CO2 evolution. Scale removal with organic dissolvers (Acetic acid) proved successful because it maintained low PH which prevented re-precipitation of acid products. With this approach scale re-deposition was delayed ranging from nine days to nine months.

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