Scale Formation in Reservoir and Production Equipment During Oil Recovery. IV. Experimental Study of BaSO4 and SrSO4 Scaling in Steel Tubings.

Abstract

Precipitation experiments with BaSO4 and SrSO4 in steel tubings were performed in order to obtain knowledge about the scaling mechanisms for these minerals. Two waters, one containing Ba2+ (or Sr2+) the other SO42-, were mixed at the entrance of the tubing, and the amount of scale formed in the tubing and the concentration of barium (or strontium) ions in the water flowing in the pipe were measured. The temperature was 40-degrees-C, the flow rates 4-6 dm3/min, inner tube diameters 8-20 mm, duration of each experiments less-than-or-equal-to 4 h. Equimolar solutions of the two minerals were used, and the initial cation concentrations were approximately 30 (Ba2+) and 10 (Sr2+) times the equilibrium concentration. The presence of an initial thin layer of BaSO4 (SrSO4) on the inside tubing wall resulted in the growth of scale from the very beginning of the experiment. About 95 % of the precipitated BaSO4 was deposited as scale when prescaled tubings were used, while only around 75 % was found as deposit when initially clean steel tubings were used. Only about 65 % of the precipitated SrSO4 was deposited as scale under similar conditions with prescaled 9 and 11 mm tubings. A comparison between experimental data and model calculations shows that the model is capable of predicting Ba2+ and Sr2+ concentration profiles in the water phase. The amounts of BaSO4(s) and SrSO4(s) predicted at the different locations in the tube are underestimated. This underprediction is due to nucleation and particle transport processes which are not accounted for in the model. A linear relationship is indicated between the surface area for crystal growth and the inverse tube radius. The surface areas per unit volume, s, for BaSO4 and SrSO4 precipitation are s(BaSO4) = 18/r and S(SrSO4) = 21/r.