(772e) Development and Evaluation of an Iridium Oxide Based Chemical Sensor for Downhole CO2 Monitoring

Geological carbon sequestration represents a long-term storage of CO₂, in which large-scale CO₂ is injected into the subsurface geologic formations, such as the deep saline aquifers or depleted oil and gas reservoir. In the CO₂ sequestration process, the injected CO₂ is expected to remain in the reservoir and not to migrate to surface. To better understand the CO₂ movement undersurface and obtain real time information in carbon sequestration, a gas-permeable-membrane-based Severinghaus-type CO₂ chemical sensor was constructed and tested in this study. The CO₂ sensor was designed and constructed based on the intersection inspiration from electrochemistry inspiration. The principle of the CO₂ sensor design is dramatically based on the pH detection the electrolyte solution which generated by the hydrolysis process of CO₂.The developed CO₂ sensor includes a couple of Iridium-oxide electrodes (To meet this purpose, iridium oxide nanoparticles was electrodeposited on the surface of gold substrate), a thin gas-permeable silicone membrane, a porous metal supporting material, and the bicarbonate-based electrolyte solution. The sensor was tested in the solution with different concentrations of CO₂ and displayed very good CO₂ sensing performance under pressures of 1000, 2000,and 3000 psi. A linear relationship between the sensor response potential and the logarithm of the CO₂ concentration was obtained for the sensor under different pressures. Reproducibility of the sensor was examined and the results indicated that the sensor displayed excellent reproducibility. CO₂/brine coreflooding tests were carried out to evaluate the performance of the CO₂ sensor in simulate CO₂ storage process. The results indicated that the sensor could detect CO₂ movement in the tests. Further studies showed that the sensor could be reused by brine flooding after CO₂/brine flushed the core. The results of the core flooding tests demonstrated that the sensor had potential application for CO₂ monitoring in carbon storage.

Differed from the traditional sensor, this type of the CO₂ sensor used an iridium-oxide electrode instead of a glass electrode to improve the resistant ability for the harsh downhole environments encountered. To fabricate the pH sensor, the as-prepared working electrode is electrochemically deposited with iridium oxide nanoparticles as the deposition solutions. This creative and simple composition method was successfully reduced the preparation time for the electrodes and stabilized the performance of the sensor Up to date, this Severinghaus-type sensor will be the first downhole, chemical CO₂ sensor for monitoring CO₂ movement under simulated reservoir conditions. And that will generate an invaluable effect for large-scale storage of CO₂. Distinct from all other monitoring methods, this small size chemical sensor is easy to handle and could provide the monitoring data continuously, timely and accurately.