Fiber Optic O2/CO2 Sensor to Monitor Atmospheric Leakage at CO2 Injection Sites

The storage of industrially generated carbon dioxide (CO2) in deep geologic formations is being seriously evaluated as a method for reducing carbon dioxide emissions to the atmosphere, and CO2 injection is being used for enhanced oil recovery, leaving two thirds of the CO2 stored underground. Reliable and cost-effective monitoring is required to demonstrate that the geologic storage is safe and effective. However, continuous monitoring of CO2 to detect leakage to the atmosphere is still a challenge. Desirable analytical systems will cover large areas, monitor continuously, operate for years with little or no maintenance, be cost effective, and differentiate between CO2 variations due to natural processes and those due to leaks of exogenous gas. Intelligent Optical Systems proposes to develop fully distributed fiber optic sensors for the simultaneous monitoring of CO2 and oxygen (O2) near the surface, to detect and unequivocally identify gas leaks at CO2 injection sites. Near-surface sensor deployment will enable us to detect CO2 leaking into the atmosphere, and at the same time the ratio between the two gases will unequivocally differentiate background processes such as biota metabolism and methane oxidation from reservoir leakage.[1] Furthermore, this combined monitoring will eliminate the need for baseline monitoring prior to injection, simplifying system installation in ongoing injections sites, resulting in a significant market advantage. In the proposed system, the entire length of an optical fiber (hundreds or thousands of meters) is the sensor. Thus, a single unit can cover the large areas important for CCUS applications, providing a huge cost reduction compared with the large numbers of single-point sensors that provide the only alternative to distributed monitoring The proposed sensor technology consists of an innovative cable that contains multiple optical fibers, each of which is responsive to a target gas. Carbon capture and sequestration may ultimately contribute to up to 20% of carbon dioxide-emission reductions over the coming century. Worldwide, annual carbon dioxide emissions from human activity are accounted to be more than 33 billion tons. Over 60% of CO2 emissions come from sources that are potentially amenable to carbon dioxide capture. Estimated costs for monitoring geologic storage over the full life-cycle of a project range up to $0.10 per ton of CO2, which gives an idea of the important market opportunity for monitoring technology. Injection of CO2 for Enhanced Oil Recovery extends the potential market for the proposed technology.