Hard scales like barium and strontium sulfate have proven to be extremely difficult to remove from well completion by existing mechanical or chemical means.

A North Sea operator recently experienced scale deposits, which were identified to be barium sulfates, in the side-pocket mandrels of a gas-lift completion. Valves could not be retrieved and so a failure would have resulted in a workover. Solvent soaking together with agitation with a wireline brush, which had been successful in the accessible area of the TRSV, was ineffective in removing enough scale to allow kickover tools to function.

A new through tubing technique to selectively remove hard and inert scales has been in development for several years. The method is based on abrasive jetting technology using a new coiled tubing tool and consists of pumping specially manufactured particles through a rotating nozzle. These particles are softer than the tubular material yet hard enough to break the scale.

This paper describes the first use of the technology in the North Sea. Used in conjunction with coiled tubing, the technique was successful in removing enough of the scale for the kickover tool to engage, latch and pull the valve. Photos of the cleaned valve, post job Gamma Ray logs and solids analyses show clearly that the majority of the scale had been removed.

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