Fiber Optic Distributed Chemical Sensors for Environmental Impact Monitoring in Carbon Sequestration

Technical and economical assessments suggest that over the next century the capture and storage of carbon dioxide in deep reservoirs (CCS) may contribute up to 20% of CO2-emission reductions. Reliable and cost-effective monitoring is required to demonstrate that CCS is safe, does not create adverse environmental impacts, and is an effective technology to control CO2 emissions. To meet this goal, a wide variety of monitoring techniques, including vadose zone and atmospheric gas measurements, and the laboratory analysis of groundwater quality, have been proposed and are being evaluated. Current methods of the direct analysis of groundwater, and gas leakage detection in the vadose zone using point sensors, are not cost-effective for large areas and long-term monitoring. Intelligent Optical Systems (IOS) proposes to develop robust distributed fiber optic sensors that will eliminate the need for point sensors for groundwater protection and vadose zone monitoring. In the proposed system, the entire length of an optical fiber will be a sensor that is capable of covering a large area and a range of depth (100s of meters). Carbon dioxide, and other acid chemical, present in the injection gas leaking from a deep storage reservoir are likely to intercept groundwater resources, resulting in a decrease of pH and an increment in water salinity. As a result of pH change, a secondary effect on metal ion concentrations, depending on the soil composition, will also take place. Our unique system will be use for the in situ determination and profiling of the pH and the dissolved CO2 concentration, in aquifers. The capability of the proposed sensors to operate only in water, but also in gaseous phase, will also allow gas leakage in the vadose zone to be rapidly detected. The system will incorporate sensors to detect CO2 and the leakage of H2S, a toxic gas that may be present in the CO2 injected. This will provide that sensor system with a unique characteristic for CCS monitoring. Commercial distributed fiber optic sensors for subsurface pressure and temperature monitoring are gaining market share in oil and gas extraction. The excellent acceptance of these systems, and the know-how gained by oil companies in the use of fiber optic sensors in this field, will facilitate the entrance of IOS’s proposed technology to the worldwide CCS market. IOS leadership in distributed chemical sensor products put us in a privileged position to develop the proposed multi-parametric system based on fiber optic sensors.