Performance analysis of a scale inhibitor in carbonated water using a dynamic method

In the oil industry, ensuring production flow assurance is challenging in pre-salt settings characterized by high pressures and temperatures, increased salinity, and the presence of carbon dioxide (CO₂). Thus, the precipitation and deposition of inorganic salts, especially calcium carbonate (CaCO₃), can compromise operational continuity, necessitating an assessment of scale inhibitor efficiency. This study investigated how CO₂ dissolution in brine affects both scale formation and the efficiency of a scale inhibitor at 120 °C, 116 psi, and an ionic composition representative of production operations, using an approach based on the dynamic Tube Blocking Test (TBT) method. The experimental unit used in this work made it possible to determine the time required for saline deposits to block a capillary tube during the flow of a saline solution containing dissolved CO₂. Different concentrations of a phosphonate-based inhibitor (2.5 and 10 mg L⁻¹) were assessed both in the absence and in the presence of CO₂. The results indicated that the addition of CO₂ to the medium promoted solution acidification through carbonic acid formation, modifying the carbonate/bicarbonate balance and changing the speciation towards more soluble forms. This pH reduction delayed the onset of CaCO₃ deposition, increasing the blockage time in the TBT. The presence of the inhibitor in a carbonated medium prolonged the scaling time relative to the system devoid of CO₂, suggesting that the gas diminished the effective supersaturation and prolonged the inhibitor's efficiency. The findings suggest that in production situations including dissolved CO₂, there is potential to optimize scale inhibitor dosage, contingent upon appropriate consideration of pH control and CO₂ partial pressure in the formulation of scale control techniques.