Investigating the Influence of Water Cut on Naphthenate Precipitation in Oil Production Facilities

Abstract

Naphthenic acids occur naturally in crude oils and can under certain conditions react with metal ions from produced water to form naphthenates. Precipitation of naphthenates can lead to serious problems in oil production facilities. Prediction of naphthenate precipitation is an important step toward early detection and resolution of their associated problems. Developing a method that will accurately predict precipitation of naphthenates in surface facilities and separators is of great value to the industry. In this paper, the principle of metal naphthenate formation is discussed. Experiments were conducted to investigate the effects of synthetic brine on naphthenic crude oil. The results were used to establish the relationship between produced water and the amount of naphthenate deposits. The experiments used a crude oil that has been classified as containing naphthenic acid and a laboratory-prepared synthetic brine. The pH of the brine was adjusted to suit the condition required for the experiment. Results show that increased water cut greatly influences the amount of precipitates. pH of subsequent mixtures increases as the volume of the brine is increased for each successive experiment. Precipitation of naphthenates occurs due to chemical reactions between the ions in both the brine and the naphthenic acid. It is established that as the produced water from reservoir increases, the amount of precipitates formed also increases since there are more ions made available for the chemical reaction. Maximum deposition of naphthenate precipitates occurred at 67 % water cut. The mass of precipitate measured at this water cut was 88 mg from 10 ml of crude oil and 136 mg from 20 ml of the same oil.