Calcium naphthenate deposition is among the mostchallenging obstacles to high production regularity foroilfields where acidic crude oils are produced. Until now it hasgenerally been acknowledged that the deposit is made up ofcalcium soaps of the naphthenic acids in the crude oil, thoughwith a slight overrepresentation of the lighter acids. In thispaper, however, we demonstrate that this is not the case.Through a combination of several analytical techniques – themost important being Potentiometric Titration, LC/MS, NMR,and VPO – the ARN acid has been identified as thedominating constituent of these deposits. The ARN acid is afamily of 4-protic carboxylic acids containing 4 - 8unsaturated sites (rings) in the hydrocarbon skeleton with moleweights in the range 1227 – 1235 g/mol. The mole weight ofthe homologous ARN acids series are 1227, 1229, 1231, 1233,1235 (basic structures) + n×14 (n = number of additional CH2-groups in hydrocarbon skeleton). The ARN acid with moleweight 1231 has C80H142O8 as empirical formula.The present paper describes the different analyticalmethods leading to the ARN acid discovery. Furthermore itdiscusses possible ARN structures and methods forquantitative ARN detection in crude oils. The ARN acid hasproved to be the main component in naphthenate deposit fromoilfields offshore Norway, Great Britain, China and WestAfrica. The implications of the discovery to current calciumnaphthenate treating strategies will be briefly discussed.
展开▼
