Field System for Extended Range Continuous Monitoring of Near Surface CO2 Gas from Multiple Locations

A novel system was developed for continuous measurement of near surface carbon dioxide gas concentrations associated with the monitoring of carbon dioxide capture and storage in geologic formations. In the current configuration, the battery powered system allows for near surface CO2 gas collection (0-300,000 ppm) from seven (expandable) independently located steady state chambers. Each chamber has an associated pump and metering valve attached to a control manifold that either directs the flow to the analyzer (test chamber) or to exhaust (all others). The uniquely large concentration range in which the system is capable of operating is achieved by using an auto-control system that senses when the LiCor LI-7000 analyzer is approaching saturation and then dilutes the incoming sample using a metered flow of nitrogen gas from the reference gas supply. The dilution is carried out in stages and is capable of increasing or decreasing on the fly to keep the analyzer within range. By reading in the sample flow rate, the dilution gas flow rate, and the output flow it is possible to calculate a dilution scalar that acts as a multiplier for the LiCor analyzer concentration, allowing for immediate read and record of true sampler concentrations. This system was tested and validated during a week of continuous operation and field use, monitoring the seven chambers 24 hours/day with CO2 concentrations ranging from background to over 130,000 ppm.