Using autonomous underwater gliders for geochemical exploration surveys

Abstract

Offshore exploration commonly uses geochemical sniffer technologies to detect hydrocarbon seepage. Advancements in sniffer technology have seen the development of submersible in-situ methane sensors. By integrating a Franatech laser methane sensor onto an autonomous underwater glider platform, geochemical survey durations can be increased, and associated exploration costs reduced. This paper analyses the effectiveness of methane detection using the integrated system and assesses its practical application to offshore hydrocarbon seep detection methods. Blue Ocean Monitoring surveyed the Yampi Shelf, an area with known oil and gas accumulations, and observed hydrocarbon seeps on the North West Shelf of Australia. Results from the survey showed a background dissolved methane concentration of 3 to 4 volumes per million (vpm). A distinct plume of methane between 30 to 84 vpm measured over 24 km2 was detected early in the survey. Three smaller plumes were also identified. Within a small plume, the highest concentration of methane was detected at 160 vpm. Methane above background levels was observed within 8 km of previously identified seeps; however, these seeps were unable to be pinpointed. Comparisons with data from previous surveys suggest similar oceanographic influences on the behaviour of the seeps, including tidal variations and the position of the thermocline. The results demonstrated that the integrated system may be used to effectively ground truth remote sensing interpretations and survey areas of interest over long durations, providing methane presence or absence results. To this effect, the integrated system may be implemented as a supporting technology for assessing the risks of further funding hydrocarbon detection surveys and focusing the area of interest before the deployment of vessel-based surveys.