ABSTRACT
About 50% of all oil reservoirs worldwide are based on carbonate minerals (limestone/chalk/dolomite) and about 50% are sandstone (quartz, feldspar, etc.), although they can also contain a small percentage carbonate minerals. Acid stimulation is used to increase permeability both in production and injector wells, carbonate or sandstone, by dissolving various acid-soluble solids naturally present in the rock matrix or as formation damage. There are many types of formation damage only some of which can be treated with acids; for example, organic deposits such as wax and asphaltenes cannot be treated. This section on acidizing should also be read together with the section on scale dissolvers in Chapter 3 on scale control since low-pH acidizing will also remove carbonate and sulde scale deposits. To chemically remove sulfate scale, high pH chelates such as salts of polyaminocarboxylic acids are used.
