Testing Ground Penetrating Radar and Ethane Gas Sensing to Detect Oil in and Under Ice

摘要

There is a worldwide need to develop practical remote sensing systems to detect and map oil in and under ice. Such systems would facilitate leak detection and greatly improve spill response capabilities in ice-covered waters. This paper presents results from November 2004 tests with oil spilled under an ice sheet grown from urea-doped water at the Cold Regions Research and Engineering Laboratory (CRREL) in Hanover, NH. Two independent technologies were evaluated: high-frequency pulsed Ground Penetrating Radar (GPR) incorporating measurements of changes in amplitude with increasing offset (AVO analysis), and a highly sensitive ethane gas sensor. The objective was to establish whether currently available sensors and software associated with both systems could detect oil encapsulated within and trapped under solid ice.rnBoth systems tested at CRREL detected the presence of oil trapped in and under ice. In many respects, this test program represents a more severe case than a real spill under more variable, thicker sea ice, which would potentially involve larger, thicker oil pools and natural cracks and fractures. The promising results reported here represent a significant development in developing practical solutions to the oil-in-ice detection problem.rnFresh South Louisiana crude was injected inside plastic skirts frozen into the ice. Spill volumes ranged from 49 to 188 litres, representing a range of nominal oil thickness from 8 to 30 mm. Six spills in smooth ice included three sites with trapped oil within the ice sheet and three sites with free oil under the ice sheet. A seventh spill was made in rubble ice of variable thickness with a rough undersurface.rnA series of 2D and 3D experiments were completed 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.