UNC-CH Physics and Astronomy Colloquium

Mark Conradi, Washington University

“Earth’s Field NMR to Detect Spilled Oil Trapped under Arctic Ice”

Oil production from wells in the arctic sea must face the possibility of leakage.  Spilled oil would try to rise to the surface, but would be blocked by the 1-2 meters of ice coverage.  ExxonMobil wants a detection method in-place before drilling or production begins.

Nuclear magnetic resonance can detect the abundant hydrogen nuclear spins of oil (and, unfortunately, water).  The device uses a detection coil large enough to reach through the ice, 6 meters in diameter.  The apparatus is flown by helicopter and then set onto the ice for detection.

Three physics issues arose in implementing the NMR solution.  (1) Pre-polarization is used to align the nuclear spins to a greater extent than the earth’s field can. This field must be intense and the stored energy must be removed rapidly, leading to innovative switching circuitry.  (2) The resonant pulses are frequency swept and must be adiabatic.  Pulses were designed that avoid interference from the counter-rotating field component.  (3) The signal of the oil must be distinguished from the much greater signal from sea water; this relies on the differences in the oil relaxation times compared to water.