Abstract

Scale formation is one of the most serious oil field problems that inflict water injection systems primarily when two incompatible waters are involved. Two waters are incompatible if they interact chemically and precipitate minerals when mixed. Due to the lack of reaction kinetics data, the rate of barium sulphate deposition in porous rock was measured through flooding sandstone core samples of uniform properties with supersaturated brine. The brine was formulated at the core inlet by mixing of injected sea water and formation water that contained high concentration of barium ion at various temperatures (50 - 80°C) and differential pressures (100 - 200 psig). The rate of BaSO4 scale formation was estimated by monitoring the core effluent’s barium ion concentration. The solubility of barium sulphate scale formed and how its solubility was affected by changes in salinity and temperatures (40 - 90°C) were also studied. Scanning Electron Microscopy analysis was also used to examine the nature of scale deposition throughout the core. The results indicated increased rate of BaSO4 precipitation at higher temperatures and greater brine super-saturation. The results were utilized to build a general reaction rate equation to predict BaSO4 deposition in sandstone cores for a given temperature, brine super-saturation and differential pressures.