An industry first was achieved by successfully dissolving 200 kg of barium sulphate scale from the upper part of the tubing in a well on the Alwyn North field in the North Sea. This well experienced rapid and very severe sulphate scale build-up resulting in the tubing retrievable safety valve being stuck in the open position. A new scale dissolver was used for the first time in this operation and successfully removed enough scale to reinstate the well. A full workover was prevented with a total cost saving of about £1 million.

This paper describes the well history, the investigation, the scale removal alternatives and the laboratory tests performed on the scale dissolver. It discusses the operation design, the operation itself and the scale dissolving results and concludes with a description of the wireline re-instatement operations. It also highlights the continuous advancement in success and capability of the through tubing workover.

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