Downhole Sensor Network for Monitoring CO2 Migration

Geologic carbon sequestration (GCS) is advancing as a preferred means of mitigating CO2 emissions from fossil-fueled plants. For understanding sequestration processes and verifying GCS success at its intended function of retaining CO2 within reservoir bounds, it is essential to track and monitor the fate of liquid CO2 stored deeply at high pressure. Tools are needed for continuous monitoring over large areas the underground migration of the sequestered CO2. The proposed project will develop a laser-based sensor technology for inclusion in a network of permanently-installed, continuously operating CO2 sensors that can be deployed several thousand feet below ground via 1 diameter downholes. The system employs a tunable laser beam transmitted via optical fiber to interrogate reservoir fluid via a remote probe sensor head suspended downhole by the optical fiber cable. The novel technology will supplement PSIs ground-level laser-based sensor prototypes, operating at the Midwest Geological Sequestration Consortiums (MGSC) Validation Field Project Site in Decatur, IL, that continuously and autonomously monitor surface CO2 to detect leaks. In the proposed Phase I program, PSI will demonstrate the proof of principle that supercritical CO2 can be monitored at sequestration pressure and temperature conditions. We will extend near-infrared tunable diode laser absorption spectroscopy (TDLAS) to the challenge of mixtures of broad spectral absorbers (H2O and CO2). We will show that temperature tuning over the pressure-broadened spectra will provide the capability to determine the presence of CO2 at concentrations below 1%. We will construct an optically-accessible, high pressure and temperature test apparatus for making the necessary measurements. Finally, we will develop a top-level design for the Phase II prototype to be constructed and field tested in Phase II. Commercial Applications and Other Benefits: This network of MVA sensors will provide (1) improved understanding of CO2 storage and transport processes, (2) a system for continuous monitoring of migration of stored CO2, and (3) assurance of storage reservoir efficiency and stability, including protection of neighboring property and aquifers. Commercial sensor sales are envisioned worldwide for GCS programs and research, oil and gas industry, deep seawater inorganic carbon characterization, and in monitoring supercritical carbon dioxide applications (solvent, refrigerant, sterilizer, reagent).