Abstract
The performance of electrical resistivity tomography (ERT) in boreholes is studied numerically regarding changes induced by CO2sequestration in deep saline reservoirs. The new optimization approach is applied to generate an optimized data set of only 4% of the comprehensive set but of almost similar best possible resolution. Diverse electrode configurations (mainly tripotentialαandβ) are investigated with current flows and potential measurements in different directions. An extensive 2.5D modeling (>100,000 models) is conducted systematically as a function of multiparameters related to hydrogeology, CO2plume, data acquisition and methodology. ERT techniques generally are capable to resolve storage targets (CO2plume, saline host reservoir, and impermeable cap rock), however with the common smearing effects and artefacts. Reconstructed tomograms show that the optimized and multiply oriented configurations have a better-spatial resolution than the lateral arrays with splitting of potential and current electrode pairs between boreholes. The later arrays are also more susceptible to telluric noise but have a lower level of measurement errors. The resolution advance of optimized and multiply oriented configurations is confirmed by lower values for ROI (region of index) and residual (relative model difference). The technique acceptably resolves targets with an aspect ratio down to 0.5.
Highlights
The need to manage the global CO2 emissions for mitigating the greenhouse effect has led to a world wide research to reduce atmospheric CO2
The overall average rms-error for all inverted data sets approaches 0.9% with a nearly similar distribution between tomograms inverted by the robust L1 norm and their corresponding models of the L2 norm
Electrical resistivity tomography (ERT) techniques in boreholes are powerful in monitoring intrinsic property changes for storing the resistive CO2 in conductive saline reservoirs
Summary
The need to manage the global CO2 emissions for mitigating the greenhouse effect has led to a world wide research to reduce atmospheric CO2. Extensive, systematic numerical ERT 2.5D modeling is carried out, and the results are analyzed for different virtual scenarios of injected wedge-like CO2 plumes (dimensions, SCO2 or ρ) as a function of electrode configuration, burial depth, AR, data noise, and setup parameters of modeling constraints (mainly regularization parameters, see sections). The technique’s robustness in the field is tested by adding three different random errors to data sets These studies aim to test the capability of (non-)standard and optimized ERT techniques (partly developed here) to resolve the subsurface CO2 storage targets as a function of diverse parameters related to hydro-/geologic and geochemical subsurface properties (mainly of saline reservoir and cap rock), αvc (CPPC). They are contained in Hagrey [2, 14, 15] and Hagrey and Petersen [21]
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