Scaling is a major problem in any oil field. Calcite or Calcium Carbonate (CaCO3) and Celesite or Strontium Sulphate (SrSO4) are the common type of scales encountered in oil field operations. various fluids (e.g. Brine, liquid and gaseous hydrocarbons and other gases) mix in the reservoir and/or wellbore under varying thermodynamic, kinetic and hydrodynamic conditions resulting into scale formation. While CaCO3 scales are possible to be removed by the use of common acids, Strontium and Barium Sulphate require special formulations to remove.
Laboratory investigations for characterization of scales recovered from a well of Bombay High and their removal from down hole equipment and wellbore by chemical treatment have been carried out.
Produced water and injected water has been analyzed for ionic composition to monitor scale formation tendencies. The possibility of formation of Strontium Sulphate (SrSO4) scales in wellbore and tubing is well established from these analysis. Further, the well production decline in some of the wells were analyzed and corroborated with formation of scale which were later confirmed during workover.
The dissolution of Strontium Sulphate scales with special chemicals / formulations have been upto 75% under laboratory conditions, whereas other conventional solvents/chemicals were not effective for dissolution.
Accordingly squeeze treatment with chemicals for scale removal from formation face, perforations and down hole equipment's was recommended. These treatments has been carried out in some wells and results have been very rewarding.
This paper presents the results of these evaluations and field applications of scale treatment.