Scale formation is the deposition of sparingly soluble inorganic salts from aqueous solutions.1 There is another type of scale containing metal ions in which the anions are organic carboxylates or naphthenates. This is discussed in Chapter 7. Scale can deposit on almost any surface so that once a scale layer is first formed it will continue to get thicker unless treated (Figure 3.1).2 Scales can block pore throats in the near-well bore region or in the well itself causing formation damage and loss of well productivity. They can deposit on equipment in the well, such as electric submersible pumps or sliding sleeves, causing them to malfunction. Scale can occur anywhere along the production conduit narrowing the internal diameter and blocking flow and, finally, scale can form in the processing facilities. Next to corrosion and gas hydrates, scale is probably one of the three biggest water-related production problems and needs to be anticipated in advance to determine the best treatment strategy. For some fields, scale control can be the single biggest operational cost.3