The Discovery of High Molecular Weight Naphthenic Acids (ARN Acid) Responsible for Calcium Naphthenate Deposits. (2005)

The Discovery of High Molecular Weight Naphthenic Acids (ARN Acid) Responsible for Calcium Naphthenate Deposits. Heidi Mediaas; Heidi Mediaas Statoil ASA Search for other works by this author on: This Site Google Scholar Nick O. Wolf; Nick O. Wolf ConocoPhillips Co Search for other works by this author on: This Site Google Scholar Thomas David Baugh; Thomas David Baugh ConocoPhillips Search for other works by this author on: This Site Google Scholar Knut V. Grande; Knut V. Grande Statoil ASA Search for other works by this author on: This Site Google Scholar Jens Emil Vinstad Jens Emil Vinstad Statoil ASA Search for other works by this author on: This Site Google Scholar Paper presented at the SPE International Symposium on Oilfield Scale, Aberdeen, United Kingdom, May 2005. Paper Number: SPE-93011-MS https://doi.org/10.2118/93011-MS Published: May 11 2005 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Get Permissions Search Site Citation Mediaas, Heidi, Wolf, Nick O., Baugh, Thomas David, Grande, Knut V., and Jens Emil Vinstad. "The Discovery of High Molecular Weight Naphthenic Acids (ARN Acid) Responsible for Calcium Naphthenate Deposits.." Paper presented at the SPE International Symposium on Oilfield Scale, Aberdeen, United Kingdom, May 2005. doi: https://doi.org/10.2118/93011-MS Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex Search nav search search input Search input auto suggest search filter All ContentAll ProceedingsSociety of Petroleum Engineers (SPE)SPE International Oilfield Scale Conference and Exhibition Search Advanced Search AbstractCalcium naphthenate deposition is among the most challenging obstacles to high production regularity for oilfields where acidic crude oils are produced. Until now it has generally been acknowledged that the deposit is made up of calcium soaps of the naphthenic acids in the crude oil, though with a slight overrepresentation of the lighter acids. In this paper, however, we demonstrate that this is not the case. Through a combination of several analytical techniques - the most important being Potentiometric Titration, LC/MS, NMR, and VPO - the ARN acid has been identified as the dominating constituent of these deposits. The ARN acid is a family of 4-protic carboxylic acids containing 4 - 8 unsaturated sites (rings) in the hydrocarbon skeleton with mole weights in the range 1227–1235 g/mol. The mole weight of the homologous ARN acids series are 1227, 1229, 1231, 1233, 1235 (basic structures) + n×14 (n = number of additional CH[2]-groups in hydrocarbon skeleton).The ARN acid with mole weight 1231 has C[80]H[142]O[8] as empirical formula.The present paper describes the different analytical methods leading to the ARN acid discovery. Furthermore it discusses possible ARN structures and methods for quantitative ARN detection in crude oils. The ARN acid has proved to be the main component in naphthenate deposit from oilfields offshore Norway, Great Britain, China and West Africa.The implications of the discovery to current calcium naphthenate treating strategies will be briefly discussed.IntroductionAn increasing share of the oilfields found and developed around the world falls in the category "high-TAN crudes", i.e. contains significant amounts of carboxylic (mainly naphthenic) acids. Producing and refining high-TAN crude oils introduces a number of problems, among which calcium naphthenate deposition in process facilities is the most serious production issue.[1–4] The mechanistic understanding of calcium naphthenate deposition is still very limited, though. It is generally acknowledged that a reaction takes place between naphthenic acids in the oil and calcium ions in the water. The reaction product, calcium naphthenate, is basically insoluble in either of the phases and, hence, precipitates out and accumulates at the oil/water interface. Although this simple model describes the naphthenate deposition phenomenon nicely, it doesn't give any clue as to why the acids in the deposit do not resemble the acids in the crude oil (Mediaas et al.[5] have titrated acids isolated from a calcium naphthenate deposit sample and from the corresponding crude oil to show that the average mole weight of the former is significantly lower than that of the acids in the crude oil; 330 and 430 g/mol, respectively). Furthermore, in some cases, it takes only a few parts per million of a naphthenate inhibitor to suppress naphthenate deposition from oil and water containing 2 wt% naphthenic acids and 0.1 wt% calcium, respectively.[1] Together, these observations indicate that some rigid selection criteria direct which naphthenic acids are active in the naphthenate deposition process. These are nothing but field observations confirming laboratory experiments showing that high pH (~10 or higher) and high reactant concentrations are needed for detectable amounts of ordinary organic (including naphthenic) acids to deposit as calcium salts.[2]ConocoPhillips and Statoil have cooperated for several years to unravel the fundamental secrets of calcium naphthenate deposition. Our working hypothesis has been that the reason for the above described "discrepancies" between the model and field- and laboratory observations is that one or more specific structural elements need to be present in a naphthenic acid in order to render it receptive to deposition upon contact with calcium-containing water at pH ~6. The objective has been to identify structural keys that enable naphthenic acids to deposit as calcium naphthenate under production conditions. The first fruit of this cooperation - the identification of the ARN acid as a prerequisite for calcium naphthenate deposition - was presented at the ACS National Meeting in August 2004.[6] In this paper we will elaborate somewhat more on the ARN acid discovery before we present our present ideas regarding the structure of the ARN acid. Keywords: ester, spectrum, discovery, naphthenic acid, naphthenate deposition, calcium naphthenate deposition, acid group, acid, fragment, chromatography Subjects: Improved and Enhanced Recovery This content is only available via PDF. 2005. Society of Petroleum Engineers You can access this article if you purchase or spend a download.