Downhole Sensors for Monitoring CO2 Migration

Ensuring safety and public acceptance of Geologic Carbon Sequestration (GCS), a preferred means of mitigating CO2 emissions from fossil-fueled plants, requires novel cost-effective tools and methods for monitoring, verifying, and accounting (MVA) to detect any CO2 leakage from sequestration reservoirs. A complementary need exists for the ability to monitor the progress of the injected CO2 plume and its preferred migration paths. Requisite tools include reliable long-term sensitive, autonomous and cost- effective measurements to detect, locate, and quantify the presence of migrating or escaping CO2. We are developing a laser-based sensor for permanently-installed, downhole CO2 measurements at GCS sites. This sensor is small and robust and versatile enough to be deployed in injection, monitor, and microhole wells (~1-3 dia.) to several thousand meters depth. The system employs a tunable laser beam transmitted via optical fiber to interrogate reservoir fluid in situ via a remote probe sensor head suspended downhole. The novel technology will supplement PSIs ground-level laser-based sensor prototype, demonstrated at the Midwest Geological Sequestration Consortiums (MGSC) Validation Field Project Site in Decatur, IL. In the Phase I program, proof of principle was established for overcoming the spectroscopic challenges of laser-based absorption measurements in the extremes of the downhole environment. Laboratory measurements of high pressure and temperature CO2 and brine supported the predicted CO2 detection capabilities. Discussions with industry helped provide a greater understanding of the application needs, as well as important engineering details for downhole sensor deployment. A top level design concept was also generated as a starting point for a Phase II prototype. The proposed Phase II project entails the sequential design and construction of an Alpha and Beta prototype sensor, the former to be tested in a high pressure, high temperature laboratory chamber, and the latter to be deployed down a monitor well at a GCS research site. These efforts will be supplemented by an analysis and testing of the sensor capability on enhanced oil recovery (EOR) downhole fluids. Finally, a final design and market strategy for a commercial prototype sensor will be designed. This network of downhole sensors will provide (1) improved understanding of CO2 storage and transport processes, (2) continuous monitoring of migration of stored CO2, and (3) assurance of storage reservoir stability, including protection of neighboring property and aquifers. Commercial sensor sales are envisioned worldwide for geologic sequestration programs and research, oil and gas industry, deep seawater inorganic carbon characterization, and in monitoring supercritical carbon dioxide applications (solvent, refrigerant, sterilizer, reagent).