A Quantitative Study of Sr2+ Impact on Barite Crystallization and Inhibition Kinetics

Scale inhibitors have been widely used for barite scale control. Our group has developed several barite crystallization and inhibition models to predict the crystallization and inhibition kinetics of pure barite with different inhibitors and calculate the minimum inhibitor concentration (MIC) required. However, instead of pure barite scale formation, the incorporation of Sr2+ can be frequently found in the oilfield, because of the coexistence of Ba2+ and Sr2+ in the produced water, which can influence the kinetics of crystallization and inhibition significantly. As a result, the MIC predicted could be off significantly. Therefore, in this study, the effect of Sr2+ on barite crystallization and inhibition kinetics is quantitatively investigated to evaluate the accuracy of MIC values under various conditions. The induction time of barite with different concentrations of Sr2+ was measured by laser apparatus without or with different concentrations of scale inhibitor diethylenetriamine penta(methylene phosphonic acid) (DTPMP) at the conditions: barite saturation index (SI) from 1.5 to 1.8; temperature (T) from 40 to 70 ℃; and [Sr2+]/[Ba2+] molar ratios from 0 to 15, all with celestite SI < 0. The results show that the induction time of the barite increases with [Sr2+]/[Ba2+] ratio at a fixed barite SI, T and DTPMP dosage. That means the MIC will be overestimated if it is calculated by previous semiempirical pure barite crystallization and inhibition models, without considering the presence of Sr2+. Based on the experimental results, the novel quantitative barite crystallization and inhibition models that include the influence of Sr2+ were developed for the first time as follows: Barite crystallization model with the influence of Sr2+: l o g 10 t 0 B a S O 4 ,   S r = ( 1.523 − 10.88 S I − 895.67 T ( K ) + 5477 S I × T ( K ) + 0.829 × [ C a 2 + ] ) + ( 0.823 S I + 85.44 T ( K ) − 0.667 ) × ( [ Sr 2 + ] [ B a 2 + ] ) Barite inhibition model including the influence of Sr2+ l o g 10 ( t i n h B a s o 4 , S r t 0 B a S O 4 , S r ) = b B a S O 4 , S r × C i n h l o g 10 b B a S O 4 , S r = ( − 2.187 − 1.411 × S I + 1329.29 T ( K ) + 0.153 × p H ) + ( 0.0983 × S I − 74.66 T ( K ) + 0.099 ) × ( [ Sr 2 + ] [ B a 2 + ] ) These novel models are in good agreement with the experimental data. They are used to predict the induction time and MIC more accurately at these common Ba2+ and Sr2+ coexisting scenarios. The observations and new models proposed in this study will significantly improve the barite scale management when Ba2+ and Sr2+ coexist in the oilfield.