Role of agitation and temperature on calcium sulfate crystallization in water injection process

Water injection to reservoirs for recovery increase is a common enhanced oil recovery method in petroleum industry. Water injection might give a negative result due to scale formation and inducing damage in porous media. The compatibility study of mixed waters should be done before deciding about the water injection in reservoir. The time required for the mixture of incompatible waters to reach the maximum potential of scale at desired condition of temperature and pressure is not fully discussed in literature but it is very crucial and is highly dependent to crystallization process. This work may be proved to be of great value in understanding the crystallization process of calcium sulfate due to mixing of formation and injection waters by experimental approach. To simulate the effect of fluid velocity in porous media on the amount of precipitated scale, the experiments are done at two condition of not agitated as well as agitated one. Three zones at which primary nucleation, crystal growth or secondary nucleation controls the scale precipitation has been determined by measuring the amount of scale at different times. The results show that agitation and increasing temperature altogether have an important role on crystallization and reduction of the reaction time required to get the final potential of produced scale. The changes in crystal size and the type of precipitated scale due to temperature increase and agitation were also studied by SEM and EDX altogether at different time duration. Determination of the required velocity of injection in dynamic tests, kinetic of crystallization happening and the change in crystal size of calcium sulfate at different time duration are some of the applications of the results of this work.