The application of sulphate scale dissolvers in the production tubing in North Sea fields has been carried out, with reported success, for many years in order to remove barium and mixed sulphate scale deposits from both the wellbore and from the near-wellbore formation. As well as having the capacity to dissolve mineral scales, these corrosive materials also have the potential to cause some degree of formation damage by the dissolution of reservoir minerals. In this study, three commercial scale dissolver formulations were tested using a range of laboratory procedures to assess (a) their comparative ability to dissolve barium sulphate; and (b) of more importance in the current study, their potential to cause formation damage in the near-wellbore formation. In addition to the commercial formulations, laboratory prepared amino carboxylic acid scale dissolvers (EDTA and DTPA) were also examined. The potential formation damage capacity of the various scale dissolvers has been assessed by measuring the levels of cation release in static tests on mineral separates and also by studying the various effluent profiles from dissolver core flooding studies on reservoir sand. The potential damage mechanisms include silicate dissolution, fines generation/migration, emulsion formation/stabilization and mechanical strength reduction. We conclude that, when testing sulphate scale dissolvers for field application, their formation damage potential should be assessed as well as their barite dissolution performance.
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