Concentration and Distribution of Naphthenic Acids in the Produced Water from Offshore Norwegian North Sea Oilfields

Abstract

Naphthenic acids (NAs) constitute one of the toxic components of the produced water (PW) from offshore oil platforms discharged into the marine environment. We employed liquid chromatography (LC) coupled to high-resolution mass spectrometry with electrospray ionization (ESI) in negative mode for the comprehensive chemical characterization and quantification of NAs in PW samples from six different Norwegian offshore oil platforms. In total, we detected 55 unique NA isomer groups, out of the 181 screened homologous groups, across all tested samples. The frequency of detected NAs in the samples varied between 14 and 44 isomer groups. Principal component analysis (PCA) indicated a clear distinction of the PW from the tested platforms based on the distribution of NAs in these samples. The averaged total concentration of NAs varied between 6 and 56 mg L–1, among the tested platforms, whereas the concentrations of the individual NA isomer groups ranged between 0.2 and 44 mg L–1. Based on both the distribution and the concentration of NAs in the samples, the C8H14O2 isomer group appeared to be a reasonable indicator of the presence and the total concentration of NAs in the samples with a Pearson correlation coefficient of 0.89.

Comparison of Substance‐Based and Whole‐Effluent Toxicity of Produced Water Discharges from Norwegian Offshore Oil and Gas Installations

“…Extracts of naphthenic acid from produced water were shown to have an EC50 of 23 mg/L for S. costatum and 6.4 mg/L for A. tonsa (Frost et al, 2003). Assuming that naphthenic acid concentrations in the present study are in the same range as those measured in the past (Bertheussen et al, 2021; Mediaas et al, 2003; Samanipour et al, 2020), they could have contributed to the toxicity observed in the present WET tests. Recently, a standardized method for routine chemical characterization of the total concentration of naphthenic acids (as a group) in produced water effluents was developed (Bertheussen et al, 2021) and is currently implemented in the biannual analysis of produced water effluents on the Norwegian continental shelf.…”

“…In the past, naphthenic acids have been isolated from the effluent of installation Heidrun and were measured at concentrations of roughly 50 mg/L (Mediaas et al, 2003). Similar levels have been found in produced water more recently as well (Bertheussen et al, 2021;Samanipour et al, 2020). Toxicity to aquatic species justified considering naphthenic acids as a produced water constituent of concern (Jones et al, 2011;Thomas et al, 2009).…”

Analytics Driving Kinetics: Advanced Mass Spectrometric Characterization of Petroleum Products

“…Vanadium compounds; 296 Non-polar aromatic compounds; 297 thiols; [298][299][300] Sulfides; 301,302 N-, S-, and O-containing species; 129,198,205,207,212,214,221,224,236,244, Porphyrins; [348][349][350][351][352] Molecular structure of Asphaltenes; 185,216,353,354 naphthenic acids; 284,285,[355][356][357][358][359][360] petroleum sulfonates; [361][362][363][364] acidic compounds; 213,215,216,323,362,[365][366][367][368][369][370][371]…”

Naphthenic Acids: Formation, Role in Emulsion Stability, and Recent Advances in Mass Spectrometry-Based Analytical Methods

“…Another study detected 55 unique NAs isomer groups in PW samples from different Norwegian offshore oil platforms with carbon number ranging from 8 to 26 and Z values of 0 to −18. Based on NAs distribution and the concentration in the samples, the C 8 H 14 O 2 isomer group appeared to be an indicator of the presence of NAs in the samples [142].…”