Naphthenate precipitation is encountered when the naphthenic acids, present in acidic crude oils, interact with calcium and, to a lesser extent, other metal ions that are present in connate waters. Precipitation is often associated with a rise in solution pH. It can cause severe problems during the separation of oil and water, forming very stable emulsions and/or insoluble deposits in separators or crude dehydration/desalting vessels.
Acetic acid injection is widely used to inhibit naphthenate precipitation and remove calcium from crude oils. This has significant implications for the integrity of the process pipework and vessels. The impact of acetic acid on the corrosion of carbon steels under typical oilfield conditions is discussed. Laboratory and field data are presented to demonstrate the impact of acetic acid on corrosion rates.
A variety of mitigation options are discussed, including the impact of acetic acid on corrosion inhibition. These include the use of novel surfactants to inhibit calcium naphthenate precipitation. This type of naphthenate inhibitor has been shown to provide effective naphthenate control in the absence of any pH reduction, eliminating the detrimental effect of acetic acid injection on process pipework and vessels.