Comprehensive chemical characterization of the unresolved petrogenic components of produced water

Produced water from offshore oil production platforms represents the largest direct discharge of effluent into the offshore environment and is known to contain a complex mixture of heavy metals, dissolved organic compounds including hydrocarbons, phenols and organic acids, as well as the residues of oil production chemicals. The oil related components that are routinely monitored in produced water are BTX (benzene, toluene, xylene), alkylphenols, phenols, oil in water, selected organic acids and polycyclic aromatic hydrocarbons (PAHs). Some of the natural oil related produced water components are known to have the potential to harm the environment and affect the endocrine system with chromatographically unresolved complex mixtures of PAHs and naphthenic acids identified as the compounds responsible. There have been considerable advances over the last 5 years in analytical instrumentation and chemometric tools facilitated by the development and availability of affordable high-resolution mass spectrometric instrumentation coupled to comprehensive chromatographic techniques advanced data handling software. The project team has recently explored the chemical space of produce water via different extraction methods employing newly developed data processing approach. This exercise, at the same time, resulted in comprehensive extraction recovery assessment of produced water. As a consequence, we were able to validate the optimized extraction method for produced water. This step is of a crucial importance for future chemical characterization as well as risk assessment when dealing with produced water. Additionally, we were able to assign chemical formula to the unique features that appeared in the samples via the optimized extraction method. This was done through a validated identification workflow developed by the team. In the last year of the project a specific method for the extraction and analysis of polar and non-polar fractions of produced water was developed and validated. The method was further tested for the evaluation of naphthenic acids in produced water. Finally, in collaboration with Equinor, we measured the concentration of 180 naphthenic acids in the produced water from six different platforms from the Norwegian continental shelf. This project resulted in the first detailed concentration distribution of naphthenic acids in produced water from off-shore oil platforms.

This project enabled the first comprehensive characterization and quantification study of the NAs in PW samples. As of today, this is the most comprehensive study providing detailed chemical characterization and concentrations of NAs in the complex unresolved mixture of produced water. Our results showed a high level of diversity in the samples both in terms of detection and concentrations. The observed diversity warrants further and more comprehensive characterization of NAs in the produced water. Finally, the observed diversity also indicates the need for more investigations in order to identify a few isomer groups as markers of presence of NAs in the PW samples. Simple analytical methods and algorithms are developed and made available to the industry and the stakeholders for analysis of PW, particularly NAs.

Produced water from offshore oil production platforms represents the largest direct discharge of effluent into the offshore environment and is known to contain a complex mixture of heavy metals, dissolved organic compounds including hydrocarbons, phenols and organic acids, as well as the residues of oil production chemicals. The petrogenic components that are routinely monitored in produced water are BTX (benzene, toluene, xylene), alkylphenols (C1-9), phenols, oil in water, selected organic acids and polycyclic aromatic hydrocarbons (PAHs). Some of the natural petrogenic produced water components are known to have the potential to harm the environment and able to antagonize the estrogen (ER) and aryl hydrocarbon receptor (AhR) and antagonize the androgen receptor (AR) antagonists with chromatographically unresolved complex mixtures of PAHs and naphthenic acids identified as the responsible components. There have been considerable advances over the last 5 years in analytical instrumentation and chemometric tools facilitated by the development and availability of affordable high-resolution MS instrumentation coupled to comprehensive chromatographic techniques advanced data handling software. The project team has successfully used a number of the approaches to resolve unresolved components from various sources combined with multi-variate chemometrics statistical tools to relate the toxicity of oil isolates to specific components. Within the current proposal we have sought to focus on identifying the key toxic components of regulatory concern in produced water through the combined use of advanced analytical methods with standard toxicity tests and multivariate analytical approaches.