Laboratory study on precipitation of calcium sulphate in Berea sandstone cores

Scale deposition is one of the most serious oil field problems that inflict water injection systems, primarily when two incompatible waters are involved. Two waters are called incompatible if they interact chemically and precipitate minerals when mixed. Typical examples are sea water, with high concentration of SO4-2, and formation waters, with high concentrations of Ca+2, Ba+2 and Sr+2 . Mixing of these waters, therefore, could cause precipitation of CaSO4, BaSO4, and/or SrSO4.; Due to the lack of reaction kinetics data, the rate of calcium sulphate deposition in porous rock was measured through flooding Berea core samples of uniform properties with supersaturated brine. The brine was formulated at the core inlet by mixing two solutions containing Ca+2 and SO4-2 ions, separately. The rate of CaSO 4 precipitation was estimated by monitoring the core effluent's Ca +2 ion concentration. SEM & BMI analyses were also used to examine the nature of scale deposition throughout the core. Several parameters were varied including temperature, pressure, degree of brine super-saturation, and flooding velocity.; The results indicated increased rate of CaSO4 precipitation at higher temperatures, higher flood velocities, and greater brine super-saturation, whereas pressure had a slight effect on CaSO4 precipitation. The results were utilized to build a general reaction rate equation to predict CaSO4 precipitation in Berea sandstone for a given temperature, brine super-saturation, and flooding velocity. The equation was validated by more experimental data with-reasonable accuracy.