Development of a CO₂ Chemical Sensor for Downhole CO₂ Monitoring in Carbon Sequestration

Technical Report · Mon Dec 12 00:00:00 EST 2016

OSTI ID:1345290

Liu, Ning ^[1]

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1. New Mexico Inst. of Mining and Technology, Socorro, NM (United States). Petroleum Recovery Research Center; Univ. of Louisiana, Lafayette, LA (United States). Petroleum Engineering Dept.

Geologic storage of carbon dioxide (CO₂) has been proposed as a viable means for reducing anthropogenic CO₂ emissions. The means for geological sequestration of CO₂ is injection of supercritical CO₂ underground, which requires the CO₂ to remain either supercritical, or in solution in the water/brine present in the underground formation. However, there are aspects of geologic sequestration that need further study, particularly in regards to safety. To date, none of the geologic sequestration locations have been tested for storage integrity under the changing stress conditions that apply to the sequestration of very large amounts of CO₂. Establishing environmental safety and addressing public concerns require widespread monitoring of the process in the deep subsurface. In addition, studies of subsurface carbon sequestration such as flow simulations, models of underground reactions and transports require a comprehensive monitoring process to accurately characterize and understand the storage process. Real-time information about underground CO₂ movement and concentration change is highly helpful for: (1) better understanding the uncertainties present in CO₂ geologic storage; (2) improvement of simulation models; and (3) evaluation of the feasibility of geologic CO₂ storage. Current methods to monitor underground CO₂ storage include seismic, geoelectric, isotope and tracer methods, and fluid sampling analysis. However, these methods commonly resulted low resolution, high cost, and the inability to monitor continuously over the long time scales of the CO₂ storage process. A preferred way of monitoring in-situ underground CO₂ migration is to continuous measure CO₂ concentration change in brine during the carbon storage process. An approach to obtain the real time information on CO₂ concentration change in formation solution is highly demanded in carbon storage to understand the CO₂ migration subsurface and to answer the public safety problem. The objective of the study is to develop a downhole CO₂ sensor that can in-situ, continuously monitor CO₂ concentration change in deep saline. The sensor is a Severinghaus-type CO₂ sensor with small size, which renders it can be embedded in monitoring well casing or integrated with pressure/temperature transducers, enabling the development of “smart” wells. The studies included: (1) prepare and characterize metal-oxide electrodes. Test the electrodes response to pH change. Investigate different ions and brine concentration effects on the electrode’s performance. Study the stability of the electrode in brine solution; (2) fabricate a downhole CO₂ sensor with the metal-oxide electrodes prepared in the laboratory. Test the performance of the CO₂ sensor in brine solutions. Study high pressure effects on the performance of the sensor; (3) design and conduct CO₂/brine coreflooding experiments with the CO2 sensor. Monitor CO₂ movement along the core and test the performance of the sensor in coreflooding tests. Develop a data acquisition system that can digitize the sensor’s output voltage. Our completed research has resulted in deep understanding of downhole CO₂ sensor development and CO₂ monitoring in CO₂ storage process. The developed downhole CO₂ sensor included a metal-oxide electrode, a gas-permeable membrane, a porous steel cup, and a bicarbonate-based internal electrolyte solution. Iridium oxide-based electrode was prepared and used for preparation the CO₂ sensor. The prepared iridium oxide-based electrode displayed a linearly response to pH change. Different factors such as different ions and ions concentration, temperature, and pressure effects on the electrode performance on pH response were investigated. The results indicated that the electrode exhibited a good performance even in high salt concentration of produced water. To improve the electrode performance under high pressure, IrO₂ nanoparticles with the particle size in the range of 1-2 nm were prepared and electrodeposited on stainless steel substrate by cyclic voltammetry. It was observed that the thin film of iridium oxide was formed on the substrate surface and such iridium oxide-based electrode displayed excellent performance under high pressure for longer term. A downhole CO₂ sensor with the iridium oxide-based electrode was prepared. The working principle of the CO₂ sensor is based on the measurement of the pH change of the internal electrolyte solution caused by the hydrolysis of CO₂ and then determination of the CO₂ concentration in water. The prepared downhole CO₂ sensor had the size of diameter of 0.7 in. and length of 1.5 in. The sensor was tested under the pressures of 500 psi, 2,000 psi, and 3,000 psi. A linear correlation was observed between the sensor potential change and dissolved CO₂ concentration in water. The response time of the CO₂ sensor was in the range of 60-100 minutes. Further tests indicated that the CO₂ sensor exhibited good reproducibility under high pressure. A CO₂/brine coreflooding system was constructed to simulate the real-world CO₂ storage process. The prepared downhole CO₂ sensor was loaded in the system to monitor CO₂ movement during CO₂/brine coreflooding test. The results indicated that the sensor could detect CO₂ movement in the tests. Further studies showed that the sensor could be recovered by brine flooding after CO₂/brine flushed the core. The results of the coreflooding tests demonstrated that the sensor had potential application for CO₂ monitoring in carbon sequestration. A data acquisition system for the downhoe CO₂ sensor was developed and coded. The system converted the sensor output signal into digital data and transported the data from downhole to wellhead surface. The data acquisition system was tested and evaluated in the laboratory with the prepared sensor for data collection.

• Research Organization: New Mexico Inst. of Mining and Technology, Socorro, NM (United States)
• Sponsoring Organization: USDOE Office of Fossil Energy (FE)
• DOE Contract Number: FE0009878
• OSTI ID: 1345290
• Report Number(s): DOE-NMT-Final-FE0009878
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
54 ENVIRONMENTAL SCIENCES
CO2 Monitoring
CO2 Storage
Downhole CO2 sensor
CO2/brine coreflooding