Injectivity Impairment due to Sulphate Scaling during PWRI: an Analytical Model

Abstract

Previous work has derived an analytical model for simultaneous flow of incompatible waters in porous media with sulphate salt precipitation, determined typical values of kinetics reaction coefficient from corefloods and what the impact would be on productivity impairment during sulphate scaling. This paper extends the previous work, by modelling the injectivity impairment during simultaneous injection of incompatible waters, i.e. cation-rich produced water (PWRI) and seawater with sulphate anions. An analytical model with explicit expressions for deposited concentration and injectivity decline was developed. The location of scale deposition and the resulting injectivity impairment are calculated for a range of sensitivities, including reaction kinetics (ranging from minimum to maximum values as obtained from coreflood and field data), fraction of produced water in the injected mixture and barium concentration in produced/re-injected water. The theoretical parameter of the size of formation-damaged zone was introduced. It was found out that almost all deposition takes place in 2-4 well radii neighbourhood. Calculations show that simultaneous injection of seawater with produced water containing even decimal fractions of ppm of barium would results in significant injectivity decline. Copyright 2006, Society of Petroleum Engineers.