Mineral scaling in the oil and gas industry poses a significant challenge for flow assurance due to changes in process conditions, such as pressure and temperature changes, dissolved gases, or incompatibility between mixing waters, resulting from the waterflooding process and chemical treatment operations. This study focuses on understanding the scaling threat of common mineral scales (barite, celestine, gypsum, calcite) and the effectiveness of phosphonate inhibitors under the influence of various solution conditions, such as concentrations of background electrolytes and temperature. We propose a novel modeling scheme through the incorporation of the classical nucleation theory (CNT) [1,2] into the Mixed Solvent Electrolyte (MSE) model [3,4]. The MSE thermodynamic framework has been widely applied for modeling solubilities of numerous systems containing the scaling minerals across varying solution conditions. The strength of the framework lies in its ability to explicitly consider prevailing hydrated and anhydrous solids in conjunction with aqueous speciation in the model formulation. Especially, the MSE model is known to provide accurate estimates of scaling index/ tendency, which is a key parameter for identifying the supersaturation level of a specific solid in the solution and is a key input to the CNT. While MSE assesses scaling risk based on the scaling index, CNT provides kinetic information, i.e., an estimate of induction time, based on the continuum thermodynamic treatment of clusters. In this work, the solution chemistry of the scaling solids and the inhibitors has been first developed using the MSE model, primarily by utilizing experimental solubility data for solids and speciation data for inhibitors (as determined mainly from relevant titration curves). Subsequently, the CNT model has been parameterized using the induction time data that are available primarily from turbidimetric measurements. While the application of the CNT for scale-forming minerals in the absence of inhibitors is well established for assessing the induction time, the development of the theoretical formulation in the presence of inhibitors is still evolving. In this work, we propose a simple approximation approach to incorporate the effect of the inhibitors in the formulation of the CNT through the adjustment of the surface tension parameter. This effectively quantifies the effectiveness of multiple inhibitors on one or more scaling solids.
References
[1] A.E. Nielsen, Kristall und Technik 4 (1969) 17-38.
[2] O. Söhnel, J.W. Mullin, Journal of colloid and interface science 123 (1988) 43-50.
[3] P. Wang, R.D. Springer, A. Anderko, R.D. Young, Fluid Phase Equilib. 222 (2004) 11-17.
[4] P. Wang, A. Anderko, R.D. Young, Fluid Phase Equilib. 203 (2002) 141-176.
