Geophysical monitoring of vegetable oil emulsion biostimulation using cross-hole radar methods

Application of cross-hole radar tomographic methods for geophysical imaging and monitoring of field-scale vegetable oil emulsion (VOE) biostimulation in saturated unconsolidated sediments is investigated through a combination of petrophysical modeling, laboratory-scale experiments, synthetic forward and inverse modeling, and field demonstration at a VOE biostimulation site at Fridley, Minnesota.; The complex refractive index model (CRIM) model and petrophysical relationships between electromagnetic (EM) wave attenuation, Archie's law, and pore-fluid specific conductance were used to (1) predict VOE dielectric permittivity as a function of emulsion vegetable-oil fraction; (2) predict bulk dielectric permittivity changes resulting from VOE injection into saturated sand; and (3) develop methods to predict VOE saturation and changes in ground water total-dissolved-solids (TDS) based on measurement of radar slowness- and attenuation-differences.; The results illustrate pixel-based tomographic inversion limitations including (1) poor target resolution; (2) overestimation of target horizontal extent; (3) anomaly blurring and streaking; and (4) a general underestimation of anomaly magnitude. In contrast, using OBI, the vertical and horizontal extent and shape of the target anomalies were accurately reproduced and anomaly magnitude errors were small, consistent with the data error. In geologic environments where VOE injection is controlled by horizontally stratified sediments, OBI slowness-difference tomograms can be analyzed to estimate VOE saturation and interpreted with greater confidence than pixel-based tomograms.; Results of cross-hole radar monitoring of VOE injection demonstrate for the first time that radar-imaging methods can be used as a field scale remote sensing method for imaging and monitoring VOE biostimulation. Further more, the field study results indicate application of an appropriate inversion approach such as OBI can produce tomograms that (1) delineate VOE injectate and (2) provide a means to assess the magnitude of VOE pore-fluid displacement though estimation of VOE saturation. (Abstract shortened by UMI.)...