The observation and quantification of oil migration and binding in sediments using T2 magnetic resonance imaging

Magnetic resonance imaging (MRI) makes use of the interactions between atomic nuclei and an external, strong, magnetic field to image the distribution of these nuclei through a substance. In this study, proton MRI has been used to indicate the presence of oil in sediment. Using a multiecho spin-echo acquisition sequence, images of relative oil density, and hence concentration, and of the magnetic resonance relaxation rate, T2, were produced. T2, which is greatly influenced by molecular motion, was equated to binding between the oil and the sediment, thus, providing an almost real-time "description" of all aspects of the oil-sediment interaction including motion of the oil. The interactions among three sediments from the Tay Estuary (East Coast of Scotland) and three crude oils (Fulmar, Forties and Venezuelan) are discussed. Observation of changes in images of oil density and changes in T2, using spread sheets, allow both rates of diffusion of the oil into the sediment and changes in the binding of the oil to the sediment to be calculated. Both the Forties and Fulmar oils move more rapidly than the Venezuelan oil in all of the sediments examined, while the strength of binding is sediment dependent. Thus, the ability of MRI to distinguish between the rates of flow of the oils into the sediment and the strengths of interaction between the various sediments and oils is demonstrated.