Semiempirical Model for Predicting Celestite Scale Formation and Inhibition in Oilfield Conditions

Mineral scale formation has become a serious problem during various energy production processes, such asgeothermal energy, power production (cooling towers), or oil and gas operations. Most scales are treated with threshold scale inhibitors. Several crystallization and inhibition models have been reported to predict the minimum inhibitor concentration (MIC) needed to control the barite and calcite scales. Recently, more attention has been paid to the formation of celestite scales in the oilfield. However, no models have been developed to predict the MIC needed for celestite scale control. In this study, the induction time of celestite under wide ranges of celestite saturation index (SI = 0.7–1.9), temperature (T = 25–90 °C), ionic strength (IS = 1.075–3.075 M), and pH (4–6.7) without and with one phosphonate inhibitor (diethylenetriamine penta­(methylene phosphonic acid), DTPMP) and two polymeric inhibitors (phophinopolycarboxylate, PPCA and polyvinyl sulfonate, PVS) was measured by a laser apparatus. Based on our experimental results and literature data, a new semiempirical celestite crystallization and inhibition model has been developed based upon readily available parameters such as celestite SI (or other brine compositions) and T. Good agreement between the experimental results and calculated results from the model was found. Using this semiempirical model, the MIC needed for three commonly used inhibitors, DTPMP, PPCA, and PVS, on celestite scale control can be predicted over extensive production conditions. The developed model can fill the knowledge gap in scale management strategies for celestite in the produced waters.