The system where sulphate scaling damage occurs is determined by two governing parameters: the kinetics coefficient characterising the velocity of chemical reaction and the formation damage coefficient reflecting permeability decrease due to salt precipitation. We derived an analytical model-based method for determination of kinetics and formation damage coefficients from production well data consisting of barium concentrations in the produced water and of well productivity decline.

We analyse production data for five scaled-up producers from giant offshore field A, submitted to seawater flooding (Campos Basin, Brazil) in order to predict productivity index and to plan the well stimulation program. The wells are completed by gravel packs. Complete mixing of sea and formation waters in production well neighbourhoods in the reservoir under consideration was assumed in previous works. Using this assumption, quasi steady state model for reactive flow around production well is formulated. We obtained values of the two sulphate scaling damage parameters. The two coefficient values were used for prediction of productivity decline for these wells.

Both coefficient values as determined for five wells are inside the variation intervals for scale damage coefficients obtained from coreflood data. It allows concluding that the productivity damage in wells under investigation was caused by sulphate scaling and validates the mathematical model. It also permits to perform a reliable prediction of well productivity. The values for kinetics and formation damage coefficients as obtained from well and laboratory data are recommended for use in reservoir modelling of sulphate scaling.

Sulphate scaling can have a disastrous impact on oil production in waterflood projects with incompatible injected and formation waters. This is due to precipitation of barium / strontium sulphate from the mixture of both waters and the consequent permeability reduction resulting in loss of well productivity.

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