Laboratory study on precipitation of strontium sulphate in Malaysia sandstone cores

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 mixed. Due to the lack of reaction kinetics data, the rate of strontium 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 strontium ion at various temperatures (50°-80°C) and differential pressures (100psig-200 psig). The rate of SrSO4 scale formation was estimated by monitoring the core effluent's strontium ion concentration. The solubility of strontium sulphate scale formed and how its solubility was affected by changes in salinity and temperatures (40°C-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 SrSO4 precipitation at higher temperatures and greater brine super-saturation. The results were utilised to build a general reaction rate equation to predict SrSO4 deposition in sandstone cores for a given temperature, brine super-saturation and differential pressures. [Received: October 26, 2008; Accepted: February 3, 2009]