Electrical resistivity tomography as a tool for monitoring CO2 injection: Demonstration of leakage detection during bench-scale experiments
Abstract
Field-scale studies have shown Electrical Resistivity Tomography (ERT) to be an effective tool for imaging resistivity anomalies and monitoring infiltration events in the near subsurface. ERT also shows potential for monitoring CO2 injections, despite deployment challenges in the deep subsurface. We present results from analog bench-scale experiments aimed at evaluating the ability of ERT to quantify the volume and spatial distribution of a gas injected into a brine-saturated porous medium. We injected measured volumes of gas into translucent chambers filled with quartz sand, lined with electrodes, and saturated with a low resistivity salt solution. Between injections, a CCD camera captured high-resolution images, and an ERT data acquisition system scanned the chamber. Using the CCD images, quantitative visualization techniques resulted in high-resolution measurements of the spatial distribution and saturation of the injected gas. Direct comparison to inverted resistivity fields then provided a quantitative measure of the ability of ERT to estimate the total volume of injected gas and its spatial distribution within the chamber. We present results from two experiments designed to represent different injection scenarios: (A) low injection rate and strong capillary barrier, and (B) high injection rate and weaker capillary barrier. Results show that ERT provides good estimates of the shape, size and location of the primary gas plume, but underestimates gas content and does not detect thin pathways of gas from the injection port or within the overlying capillary barrier. However, ERT measurements did detect a change in saturation within the primary plume caused by leakage through the capillary barrier in (B), demonstrating the potential utility of ERT as a leakage-monitoring tool. Repeated ERT scans during our experiments led to degradation in data quality that corresponded with an increase in measured contact resistance. Decreased data quality over time is clearly a concern for ERT implementation as a long-term monitoring strategy and deserves further study to quantify the mechanisms responsible for the loss of data quality.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFMGC51A0922B
- Keywords:
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- 0594 COMPUTATIONAL GEOPHYSICS / Instruments and techniques;
- 1694 GLOBAL CHANGE / Instruments and techniques;
- 1835 HYDROLOGY / Hydrogeophysics;
- 1848 HYDROLOGY / Monitoring networks