Compensating for temperature variations in time-lapse electrical resistivity difference imaging

Variations in temperature during time-lapse electrical resistivity imaging (ERI) surveys introduce changes in electrical conductivity (EC). When the goal of the time-lapse ERI survey is to image changes in EC due to changes in saturation or pore water salinity, compensation must be made for the effect of temperature variations. A temperature-compensation method can approximate time-lapse ERI data with the effect of temperature variations removed. First uncompensated ERI data are inverted. The inversion model then is adjusted to a standard temperature image. Forward simulations are performed using the uncompensated inversion and the standard temperature equivalent model. The temperature-compensated simulated resistance data are subtracted from the uncompensated simulated resistance data, forming data correction terms. The data correction terms then are subtracted from the measured data to yield temperature-compensated data. Using the temperature-compensated data, inversions have been carried out on two synthetic data sets and a field example. Differencing two temperature-compensated data inversions is found to be superior to differencing two postinversion standard temperature equivalent images. Temperature compensation on the data allows temperature corrections to be applied to time-lapse difference inversion schemes and hydrogeophysical inversion where postinversion temperature-correction methods are not easily applied.