Monitoring Total Dissolved Hydrocarbons in Seawater around Offshore Oil and Gas Facilities

Abstract

Listen

Translate article

Abstract The oil and gas industry is committed to provide accurate impact assessment of its activity on the surrounding environment. To achieve this, extensive environmental monitoring needs to be performed on a regular basis around offshore installations. Many tools and techniques have been developed to meet that request. But monitoring trace hydrocarbons in seawater remains challenging. Standard methods require sampling of huge seawater volumes, are limited in terms of deployment flexibility and detection threshold for very low levels of contaminants. Due to variability over time, representativeness of spot sampling is also questioned. Passive samplers (already used to monitor specific substances in air) have been identified as a promising technique which could provide a number of analytical and practical advantages on standard techniques. However, challenges still remain to apply the technique to aquatic environment, especially in seawater. Additional research was therefore carried out to ensure validity of the tool for offshore use and total dissolved hydrocarbons monitoring. This paper presents the results of the work conducted to characterize passive sampler operating conditions and hydrocarbon uptake. Laboratory trials were conducted to experiment different types of passive samplers and to demonstrate the method robustness under conditions representative of field use. Practical aspects, including sampler preparation, analysis protocols and sample conservation, were also tested and assessed to ensure field applicability of the technique. It results that passive samplers do provide a highly sensitive measuring technique and have the potential to be usefully applied to monitor total dissolved hydrocarbons around offshore installations. Benefits include ease of use and ability to collect time-averaged samples over the time of immersion. It thereby allows detection of very low concentrations of substances and resolves issues arising from sampling variability. The technique also provides valuable indications on contaminant bioavailability and chronic exposure of ecosystems, which is key information for environmental risk assessment. As any technique, it presents constraints and limitations which will be presented. Nevertheless the tool offers a valuable complement to standard methods, especially for monitoring seawater in the vicinity of produced water discharges.