Time Lapse Electrical Imaging of Salt Affected Soil and Groundwater

This research was conducted to test the hypothesis that time-lapse electrical resistivity imaging (ERI) could be used as an effective tool for monitoring remediation of salt affected soil and groundwater. A time-lapse 3D ERI survey conducted over the span of 3 years was used to observe changes in an oilfield brine plume undergoing remediation using a tile drainage network.;ERI inversion parameters were selected to produce a model with the best agreement with collocated push tool conductivity logs, and the strongest correlation with core salinity measurements. The ERI models were transformed into salinity estimates in order to produce salt concentration maps and salt removal estimates.;A temperature correction method was developed that acted on the collected electrical resistivity data, rather than on the inversion model. A data correction was sought in order to remove the effect of inversion smoothing from the temperature correction and to compensate for temperature prior to inversion opening the possibility of using time-lapse inversion techniques. First the data were inverted to produce a model, and then the model was converted to a standard temperature equivalent model using the previously developed EC temperature relationship. The difference between synthetic datasets produced using the inversion model and the standard temperature equivalent model was used as a data temperature correction factor and applied to the collected data.;A simultaneous time-lapse inversion method was developed and compared to previously published methods. The simultaneous approach consisted of inverting the time-lapse datasets together and adding constraints, updated at each iteration, that changes between the resulting models be smooth and close to a reference difference model. Application of the data temperature correction and simultaneous time-lapse inversion produced a simple easily interpretable time-lapse image. The observed EC decreases were consistent with the concept of depression focused recharge enhancing infiltration and remediation under a slight topography low.;A theoretical model was modified to incorporate the results of an electrical conductivity (EC) temperature laboratory experiment and a linear EC temperature relationship was calibrated for the 0--25°C range. Using the linear approximation and theoretical model observed temperature and saturation variations could be accounted for in bulk EC measurements.