In certain operations in petroleum industries, such as production, stimulation, and transport, there is some risk of scale deposition. Scaling can occur when a solution becomes supersaturated, which occurs mostly if the temperature changes in the course of injection operations.Also, if two chemicals that will form a precipitate are brought together, a scale is formed, for example, if a hydrogen fluoride solution meets calcium ions. From a thermodynamic perspective, there is a stable region, a metastable region, and an unstable region, which are separated by the binodal curve and the spinodale curve, respectively.Scales may consist of calcium carbonate, barium sulfate, gypsum, strontium sulfate, iron carbonate, iron oxides, iron sulfides, and magnesium salts [1]. In the literature some monographs, for example, Corrosion and Scale Handbook [2], as well as reviews [3] on scale depositions are available. Case studies have been presented for North Sea carbonate reservoirs [4, 5] and Gulf of Mexico [6]. A more recent work focuses on green systems [7].
SCALE PREDICTIONAn overview of scale prediction and control has been presented [8]. The challenges of scale prediction at high temperature, high pressure, and high total dissolved solids and an accurate model to predict pH, scale indices, density, and inhibitor needs at these conditions have been discussed and reviewed.
CLASSIFICATION AND MECHANISMThe problem is basically similar to preventing scale inhibition in washing machines. Therefore similar chemicals are used to prevent scale deposition. Scale inhibition can be achieved either by adding substances that react with potential scale forming substances so that from the view of thermodynamics the stable region is reached or by adding substances that suppress crystal growth.Petroleum Engineer's Guide to Oil Field Chemicals and Fluids. http://dx.