Laboratory Study and Prediction of Calcium Sulphate at High-Salinity Formation Water

摘要

Scale formation is one of the most serious oil field problems that inflict water injection systems primarily whentwo incompatible waters are involved. Two waters are incompatible if they interact chemically and precipitate mineralswhen mixed. This study was conducted to investigate the permeability reduction caused by deposition of calcium sulphatein sandstone cores from mixing of injected sea water and formation water that contained high concentration of calciumion at various temperatures (50 - 80°C) and differential pressures (100 - 200 psig). The solubility of calcium sulphatescale formed and how its solubility was affected by changes in salinity and temperatures (40 - 90°C) were also studied.The morphology and particle size of scaling crystals formed as shown by Scanning Electron Microscopy (SEM) were alsopresented. The results showed that a large extent of permeability reduction caused by calcium sulphate that deposited onthe rock pore surface. The rock permeability decline indicates the influence of the concentration of calcium ions. Athigher temperatures, the deposition of CaSO4 scale increases since the solubility of CaSO4 scale decreases with increasingtemperature. The deposition of CaSO4 scale during flow of injection waters into porous media was shown by ScanningElectron Microscopy (SEM) micrographs. The results were utilized to build a general reaction rate equation to predictCaSO4 deposition in sandstone cores for a given temperature, brine super-saturation and differential pressures.