SBIR/STTR Award attributes
Geologic carbon sequestration is a key element of any carbon emissions mitigation strategy. A critical element in geologic carbon sequestration is monitoring, validation and accounting for the injected CO2 volume during and after injection. Controlled Source Electro-Magnetics (CSEM) is a geophysical technique that uses variations in electrical properties of reservoir rocks to map their fluid variations. Applied to oil and gas exploration, differences in resistivity between oil- or gas-filled reservoirs and brine-filled reservoirs can enable CSEM to image potential prospects. The reservoirs targeted for CO2 sequestration are typically brine-filled sandstone reservoirs, at depths greater than 4,500 ft. The free chloride ions contained in these reservoirs enable electric current to move with comparatively less resistance – the rocks are relatively conductive. The injection of CO2 into a brine-filled reservoir results in a solution of H2O, CO2, and chlorides (e.g., NaCl, KCl, or CaCl2) with substantially reduced conductivity (Boerner et al., 2015). The increase in resistivity is a consequence of the substantial reduction in free chloride ions present in solution, caused by the free ions binding to CO2 molecules. The change in resistivity can be an order of magnitude or more depending on the salinity of the brine, which presents a significant opportunity for measuring the extent of the CO2 brine solution plume. We have demonstrated that this can be measured in a pilot study within the DOE’s CarbonSAFE program (Brajas-Olalde et al., 2021; Strack et al., 2022a).The CSEM monitoring service would help ensure the safe and compliant operation of industrial scale CO2 storage facilities. Specifically, the CSEM system would enable operators of CCS facilities to make better judgements about the state and integrity of the storage formation, and prudent decisions on the safe operation of the facility. Additionally, the CSEM system can measure the extent of the CO2 brine plume, helping to ensure the safe operation of any storage facility, which is critical to the long-term effectiveness of carbon sequestration. The intent of the CSEM monitoring system is to complement active and passive seismic monitoring systems, to address the potential inability of seismic monitoring systems to image the extent of the CO2 brine plume. Passive and active seismic are proven imaging technologies for monitoring reservoir and caprock integrity, however there are legitimate concerns whether active seismic imaging can accurately measure the extent of the plume. CSEM imaging technology takes advantage of the large resistivity contrast between brine-filled reservoir rocks and reservoir rocks filled with a CO2 brine solution, compared to the relatively small difference in acoustic impedance between brine-filled reservoir rocks and reservoir rocks filled with a CO2 brine solution; thus, both technologies are complementary to each other.
