 Chemical compounds (corrosion inhibitors) are added to acids and other fluids to minimise corrosion of the metal in a well. These corrosion inhibitors are a crucial component of the acidising blends and, being primarily cationic in nature, they form a protective film on the tubing. In general they are sensitive to surfactants and to temperature. After a certain time depending on the type of steel, temperature and acid composition, they usually suddenly lose their effectiveness resulting in corrosion. When a large concentration of inhibitor is used, the risk exists that a large portion of the inhibitor does not adhere to the steel and enters the porous media. For a sandstone formation this will result in an unwanted change in wettability to an oil-wet state, thereby possibly reducing the production after the treatment. Effective corrosion inhibitors for highly reactive acids and higher temperatures are difficult to formulate. The combination of the trend towards deeper wells with higher temperatures and the increasing environmental restrictions are important issues. In the past, effective acid corrosion inhibitors were often based on the use of arsenic, copper or antimony. Substances like these are no longer allowed in several major production areas, for example the North Sea. Organic acids, which are often used for higher temperature applications, require different types of corrosion inhibitors. |
| Corrosion tests can be conducted at temperatures of up to about 175°C and pressures of up to 100 bar using static corrosion autoclaves prepared from hastelloy alloy B-2. Standard test coupons from commercially available field grade tubular are available. |
| The impact of acid and inhibitors on downhole elastomers can be evaluated by visual observation and changes in weight, dimensions and hardness of the exposed elastomers. |
 PanTerra Geoconsultants can independently assist in corrosion inhibitor optimisation studies or corrosion evaluation and recommendation. |
