Application of water-soluble polymers as calcium carbonate scale inhibitors in petroleum wells: A uni- and multivariate approach

Abstract

The present work aimed to evaluate water-soluble cellulose-derivative polymers as calcium carbonate scale inhibitors using univariate and multivariate methods. The performance of the products was evaluated through a dynamic tube blocking system, and the minimum effective concentration (MEC) of the inhibitors was determined. In the univariate study, performed at 1000 psi and 100 °C, the carboxymethylcellulose (CMC) proved to be efficient and chemically compatible, with a MEC of 20 and 80 mg L−1, at pH 6.5 and 7.0, respectively. The hydroxyethylcellulose (HEC) was shown to be chemically compatible, but it was not efficient. The polymers combination (10 mg L−1 of CMC and 200 mg L−1 of HEC) resulted in a significant improvement of the scale inhibition. Theoretical results (density functional theory calculations) demonstrated the mechanisms of action of CMC and HEC. The results of the multivariate study without inhibitor showed that the formation of CaCO3 scale depends significantly on flow, temperature and pH. However, with the presence of CMC, the multivariate study showed that only pH and temperature influence on the scale formation. Both studies produced a predictive equation, capable of predicting the fouling time, with and without inhibitor, from specific conditions, with an average prediction error of ~7%.