This project positively detected oil trapped in and under ice with two completely independent technologies, both of which have potential for further development and large-scale field testing. In many respects (limited size of spills, lack of natural cracks and fractures in the ice), the design of this test program represents a worst-case scenario, compared with the expected characteristics of a real spill under sea ice. In this context, the results reported here represent a significant breakthrough, especially when viewed against decades of previous work, resulting in few if any practical solutions to the oil-in-ice detection problem.
There is a worldwide need to develop a practical remote sensing system to detect and map oil in ice. Such systems will facilitate leak detection and improve spill response capabilities for oil and gas operations in Arctic regions. This project presents results from tests in November 2004 on a 35 cm (14 in) thick sea ice sheet grown at the Cold Regions Research and Engineering Laboratory (CRREL) in Hanover, NH. Two independent technologies were evaluated: high-frequency pulsed Ground Penetrating Radar (GPR), and an ethane gas sensor. The objective was to establish whether off-the-shelf technologies and sensors could detect oil under solid ice.
Fresh South Louisiana crude was injected inside six plastic skirts frozen into the smooth ice. Spill volumes ranged from 49 to 188 liters (13 to 50 gal), representing nominal oil film thickness from 8 to 30 mm (0.3 to 1.2 in). The six spills included an equal mix of trapped oil within the ice sheet and free oil under the ice sheet. A seventh spill was made in rubble ice with a rough undersurface. Analysis of the saturated headspace vapor for the oils used indicated that the ethane concentration ranged from 5000 ppmv before the test to only about 3000 ppmv at the conclusion of the field test.
The radar group completed a series of 2D and 3D experiments, utilizing two radar systems, each with three antenna configurations, ranging from 450 MHz to 1200 MHz. Radar results show a clear reflection from the ice/water interface in both the smooth ice and rough ice areas over the full range of antenna frequencies (including airborne runs up to three meters above the ice surface). At frequencies above 800 MHz, researchers observed clear, well defined frequency, phase, and amplitude anomalies where oil was known to be present at the ice/water interface and trapped within the ice. The agreement of experimental results with initial modeling indicates the potential to accurately predict GPR response to a variety of arctic spill scenarios and radar parameters. Overall, the results clearly demonstrate the potential for detecting oil under sea ice with GPR.
The LightTouch™ ethane gas sensor uses a Tuneable Diode Laser Spectrometer (TDLS), that can measure real-time concentrations to an accuracy of ~50 parts per trillion, approximately 200 times better than gas chromatographic measurements. Results show measurable, but very low, levels of ethane flux being transmitted through the ice sheet within the oiled areas. These measurements were made 2-3 days after the last four spills (under the maximum ice thickness) and 9-13 days following the initial three spills (under thinner ice). Although the ethane flux from oil trapped under these artificial, test-tank conditions was extremely small, the ice coring data demonstrated that the oil and light gases, such as ethane, had penetrated nearly to the surface of the ice within the 14 day program duration (initial spill to final day of testing). Given longer times and natural conditions, where tectonic forces would provide additional migration pathways, it appears likely that an airborne LightTouch™ detection system would be capable of detecting ethane emissions associated with a real oil spill.
Completed.