Robust Split Laser Sensor for Harsh Environment Sensing Applications

For long-term CO2 sequestration monitoring, it is important to detect elevated levels of metal contaminants such as Ca, K, Sr, etc., in soil and water as they can provide an early indication of CO2 leakage from geologic carbon storage sites. Technologies are needed for direct and in situ measurements of greenhouse gases, CO2 and CH4 for environmental monitoring. For in situ and real-time measurements, we employed a DOE-patented split laser measurement technology (SLMT) for laser-induced breakdown spectroscopy (LIBS) to measure elemental species (Na, Ca and Sr) and Raman spectroscopy to measure CO2 and CH4 under harsh environmental conditions. A significant part of the effort was devoted towards the development and testing of rugged sensors by incorporating innovative packaging and sealing of the sensor head to withstand the harsh subsurface conditions anticipated during underwater and downhole sensing applications at the various CO2 injection sites and wells. We successfully built several versions of compact and sealed prototype sensors that delivered high-energy laser pulses and were able to perform LIBS experiments for species detection of Na, Ca, Sr, Eu, and Yb and obtain limits of detection on the level of 10~25 parts per million (ppm) in aqueous solutions. The Raman spectroscopy sensor, using a cavity enhancement arrangement, was also built and successfully tested to detect CO2 in nitrogen buffer gas with a limit of detection of 3500 ppm. Based on the promising results obtained during Phase I and II, we will refine the split laser measurement technology (SLMT) to further enhance its performance and build several versions of rugged LIBS sensors for in situ, standoff monitoring of trace metals, and near-infrared (NIR) cavity-enhanced Raman spectroscopy (CERS) sensors for dissolved greenhouse gases in water and to validate its performance using laboratory experiments and field tests at CO2 injection sites and wells. The validation of these sensors using field deployment will lead to the development of robust sensors that are capable of measurements in harsh subsurface conditions, and further gain maturation for commercialization. These sensor systems will support laser induced breakdown spectroscopy (LIBS) and Raman scattering measurements of gases, liquids, and solids. There is a great need to provide inexpensive and compact measurement devices that are suitable for real-time assessment of air, water, and soil quality, which is highly important to oil and gas exploration companies, landowners, regulatory agencies, municipalities, and any organization that measures emissions and pollutants.