In the oilfield, due to the extensive use of water injection for oil displacement and pressure maintenance, many reservoirs experience the problem of scale deposition when injection water starts to breakthrough. In most cases the scaled-up wells are caused by the formation of sulphate and carbonate scales of calcium and Strontium. Due to their relative hardness and low solubility, there are limited processes available for their removal and the preventive measure such as the 'squeeze' inhibitor treatment has to be taken. It is therefore important to have a proper understanding of the kinetics of scale formation and its detrimental effect on formation damage under both inhibited and uninhibited environment.

This paper presents an experimental and theoretical study of permeability reduction of porous medium caused by scaling. Two incompatible solutions, calcium and sulfate/carbonate rich ions were injected into and calcium sulphate or carbonate generated within the porous medium by chemical reaction. Mechanisms by which a precipitate reduces permeability include solids depositing on the pore walls because of attractive forces between the particles and the surface of the pore, a single particle blocking a pore throat, and several particles bridging across a pore throat. The characteristics of the precipitate influence the extent of formation damage. Conditions such as large degree of supersaturation, presence of impurities, a change in temperature, and the rate of mixing control the quantity and morphology of the precipitating crystals.

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