Evaluation of Silica Matrix Ion Effects on Barite Scale Inhibitors

Silica is ubiquitous in oil and gas production water because of quartz and clay dissolution from rock formations. Furthermore, the produced water from unconventional production often contains high Ca2+, Mg2+ and Fe2+ concentrations. These common cations, especially iron, can form aqueous or surface complexes with silica and affect the nucleation inhibition of other scales such as barite. Thus, it is important to investigate the silica matrix ion effects on barite scale inhibitors efficiency to evaluate inhibitor compatibility with silica and common cations in produced waters. In this study, experimental conditions were varied from 50 mg/L to 160 mg/L SiO2 in the presence of Ca2+ (1,000 and 16,000 mg/L), Mg2+ (2,000 mg/L) and Fe2+ (10 mg/L) at 70°C and neutral pH conditions, all with a background of 1 M NaCl. Our laser scattering apparatus was used to study the effect of silica matrix ions on barite nucleation inhibition [Yan et al., 2015]. For the experiments with redox-sensitive cations (such as Fe2+), a novel anoxic apparatus along with laser scattering apparatus was used. Phosphonate, carboxylate and sulfonate inhibitors were tested. All inhibitors tolerated the experimental conditions with silica. The inhibition efficiency of phosphonate inhibitor DTPMP was impaired by high Ca2+ and Mg2+, and the addition of silica would not affect this result. The polycarboxylic acid inhibitor PPCA tolerated high Ca2+ and Mg2+ conditions, and adding silica did not have influence on this behavior. The polymeric inhibitors, such as PVS and PPCA, also tolerated the experimental conditions with Fe2+ and Fe-silica. Fe2+ significantly impaired the inhibition performance of DTPMP. This may be due to the formation of an Fe(II)-DTPMP precipitate. The detrimental effect of Fe2+ on DTPMP could be reduced, to some extent, by adding silica, which might be due to the formation of Fe-silica complex and the reduction of Fe2+ impact on phosphonate.