This paper presents the mechanism of scale formation by water in oil fields and suggests an accurate model capable of predicting scaling phenomena in Iranian Oilfield operations due to mixing of incompatible waters or change in thermodynamics, kinetics and hydrodynamic condition of systems. A new and reliable scale prediction model which can predict scaling tendency of common oilfield water deposits in water disposal wells, water-flooding systems and in surface equipment and facilities is developed and present. The development of the model is based on experimental data and empirical correlation, which perfectly match Iranian oil fields conditions. Furthermore the simultaneous deposition of oilfield scales and competition of various ions to form scale which is common phenomena in oil fields are reflected in the development of the model allowing the effect of each scale on the others to be taken into account. The new model has been applied to investigate the potential scale precipitation in Iranian oilfields, either in onshore or offshore fields where water injection is being performed for desalting units' water disposal purpose or as a method of secondary recovery or reservoir pressure maintenance.
Scale formation in surface and subsurface oil and gas production equipment has been recognised to be a major operational problem. It has been also recognised as a major causes of formation damage either in injection or producing wells. Scale contributes to equipment wear and corrosion and flow restriction, thus resulting in a decrease in oil and gas production. Experience in the oil industry has indicated that many oil wells have suffered flow restriction because of scale deposition within the oil -producing formation matrix and the downhole equipment, generally in primary, secondary and tertiary oil recovery operation as well as scale deposits in the surface production equipment.
Oil field scales costs are high because of drastic oil and gas production decline, frequently pulling of downhole equipment for replacement, reperforation of the producing intervals, reaming redrilling of the plugged oil wells, stimulation of the plugged oil-bearing formation, and other remedial workovers. As scale deposits around the wellbore, the porous media of formation becomes plugged and may be rendered impermeable to any fluids.
Many case histories [14,15,21,23–26,28,29,32,34–41,44–47] of oil well scaling by calcium carbonate, calcium sulphate, strontium sulphate and barium sulphate have been reported. Problems pertaining to oil well scaling in North Sea fields have been reported  and are similar to cases in the Russia where scale has severely plugged wells. Oilfields scale problems have occurred as a result of water flooding in Algeria, Indonesia in south Sumatra oilfields, Saudi oil fields and Egypt in El-Morgan oilfield  where calcium and strontium sulphate scales have been found in surface and subsurface production equipment. This study investigated scale formation and deposition in Iranian oilfields.