Mineral scale formation poses a high risk for the oil industry and needs to be remediated to avoid disruption during production.
Inorganic salt deposits exhibit various levels of severity: some can be removed by hot water (sodium chloride), others by acid (calcium carbonate), while others still are practically impossible to solubilise once formed (barium and strontium sulphate).
Scale inhibitor action is based on the disruption of nucleation and/or orderly crystal growth of the mineral scale. Inhibiting the formation of crystalline deposits by concentrations much lower than stochiometric levels has been known since 1930. The first application was the use of 1 to10 ppm of sodium hexametaphosphate to delay the precipitation of a supersaturated solution of calcium carbonate. Since then, polyphosphates and lately phosphonates have been used widely to prevent deposits of mineral salts.
Depending on the region where scale inhibition is required, these additives can be applied by continuous injection or squeeze treatment.
Continuous injection may be applied in injector wells or in producing well streams. Scale squeeze is applied into the well, where the scale inhibitor solution will be pushed into the near-well formation. After several hours, when the well is brought back into production, the scale inhibitor retained in the formation pores will be dissolved in the production fluids protecting the installation against scale precipitation. Once the concentration of scale inhibitor in the production fluids falls below a minimum level, the well will need to be resqueezed.