Paper: Scale Control Technology A Review

For years, all oilfield scales were called gyp, and gyp meant trouble. Times and methods may have changed, but gyp, or scale, still means trouble. Scale can be anything that precipitates from water. We have seen scale deposits that were pure rock salt and others that were much more exotic, such as zinc phosphates, sodium carbonate, and occasionally minute traces of gold and silver, but these are unusual. Everyday oilfield scales are calcium carbonate, calcium sulfate or gypsum, and barium sulfate. Strontium sulfate is occasionally found, usually in conjunction with barium sulfate. Corrosion products, too, can be found in scale-like deposits. Scale deposits are the result of water instabilities-supersaturated solutions are dropping out some of their burden of dissolved salts in order to approach equilibrium. Precipitation will continue until stability has been achieved. In a flowing system with continual replenishment of water, scale deposits can continue to grow, in some cases completely blocking the flow line (Fig. 1).