Fluctuation Enhanced Sensing for Monitoring CO2 Storage
Carbon-capture-and sequestration (CCS) is one way to address an increase in the global temperature caused by increased levels of greenhouse gases like CO2. Carbon-capture technologies are reaching commercial maturity, and there is now an increased focus on the sequestration side of CCS. Of three different approaches to sequestration – terrestrial, geologic or mineralization – geologic carbon sequestration is the most capable of providing immediate benefit on the scale needed to make a noticeable reduction in the amount of CO2 in the atmosphere. In geological carbon sequestration, supercritical CO2 is injected far beneath the surface into saline aquifers or depleted oil fields. Of utmost importance to this process is confirmation that injected CO2 remains in the deep geological features, and continues to do so over time so that sequestered CO2 does not find its way back into the atmosphere. The geological sequestration sites may be several thousand feet beneath the surface, which is a high pressure (~2500-4000 psi) and high temperature (~190 F) environment. In order to monitor the CO2 sequestration sites, TDA has developed an inexpensive CO2 sensor with an incredibly large measurement dynamic range which can be deployed at any point from the CO2 injection site up to the surface using existing boreholes. The sensor captures the electrical signal from interaction of CO2 with a specially designed sorbent material. Because the measurement requires no optical components, it is extremely rugged and can be deployed at high pressures and great depths in the same way as deep-sea oxygen sensors. In the Phase I we developed our sensor, based on the well characterized interaction between a metal-organic-framework (MOF) specially designed for high CO2 selectivity and absorption in the presence of N2 and water vapor. We first showed that deposition of a small film of SIFSIX-Cu-2-i MOF in polyvinyl butyral polymer (PVB) was responsive to CO2 concentrations from 5% - 100% under ambient total pressure (12 psi total pressure, pCO2 0.6 – 12 psi) with high reproducibility. We constructed a calibration curve of CO2 concentration vs. sensor response with a R2 = 0.9951. While we aimed at capturing the widest range in Phase I, we fully expect we can lower the detection range into the ppm in Phase II, which will give our sensor the widest dynamic range of any CO2 sensor. We constructed a special stainless steel pressure rig rated up to 4000 psi, and were able to record sensor signal response vs. CO2 up to 400 psi (pCO2 range 0.6 – 400 psi) ; the only reason we didn’t go higher was that we reached the end of the Phase I period of performance. Our new CO2 sensor has a number of attractive features: 1) the components are inexpensive and lightweight 2) the sensor’s simple design mean it can be used at the high pressures and high temperatures needed for the 3D monitoring of CO2 sequestration wells at multiple depths 3) the polymer film encasing the CO2 sensitive MOF material is already hydrophobic which helps depress signal interference from water. In this Phase I project we have demonstrated it is possible to design and build a MOF based sensor with much higher sensitivity and dynamic range than anything else reported in the current literature. The Phase I technology’s success provides a springboard for Phase II work which will result in a rugged, economically viable CO2 monitoring solution to monitor the CCS sited needed to reverse the effects of global warming. Our novel CO2 sensor is based on changes to the MOF substrate induced by reversable binding of CO2. By connecting this MOF film to an electrode, the CO2 binding is translated into an electrical signal we can ready out with inexpensive electronics. Furthermore, we have included in our design a resonant impedance matching circuit (also called a tank circuit) which further enhances our sensitivity to CO2/MOF interactions. In the Phase I we were able to measure the change in resonance frequency as a function of CO2 partial pressures (pCO2) from 0.6 to 400 psi (5% - 100% CO2, from 12-400 psi total pressure). Importantly, as soon as the CO2 flow ceased, the sensor response began returning to baseline. This measurement was reproducible and different for each concentration, and is important for a sensor which must tell how much CO2 is present but also whether the stimulus is still there in real time. We also designed and constructed a special pressure rig to assess the sensor response at higher pressures, and measured CO2 sensing ability up to 400 psi (27.2 atm) by the end of the Phase I period of performance. Using knowledge gained in the Phase I we have proposed a preliminary engineering design of the CO2 sensor and high-pressure casing, which serves as a starting point for Phase II. By deploying inexpensive CO2 sensors around CO2 sequestration sites both radially and at different depths, we can determine in real time whether the sequestered CO2 is staying where it has been injected. At each deployment location the frequency shift of the sensor can be readout to determine concentration of CO2 at that unique location. The frequency shift is presented in the form of a simple voltage differential which is easily interfaced with commercially available environmental control and monitoring units (ECU) which transmit data by cell tower or WiFi to a webpage for continuous monitoring. The sensor design is applicable to any sub-surface need, be it 7 ft or 7,000 feet below the surface. Our successful proof-of-concept work in the Phase I project provides us with a strong foundation for the Phase II project where we will continue to improve the range, durability and ease of application for the sensor for high pressure and high temperature use. The overall goals of the Phase II project include 1) evaluating sensor performance up to 4000 psi and 200 F 2) demonstration of the Phase II prototype functionality down bore-hole 3) completing construction of the chip-sized automatic frequency adjustment deployed at the sensor to maximize sensitivity and 4) continue to engage key stakeholders for input to transition this technology into wide use to drive widespread carbon sequestration.
- Research Organization:
- TDA Research, Inc.
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- SC0021501
- OSTI ID:
- 1834024
- Type / Phase:
- SBIR (Phase I)
- Report Number(s):
- TDA-R-2101-032-PhIFinal; TDA R-2101-032
- Country of Publication:
- United States
- Language:
- English
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