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Proceedings Paper

MOEMS pressure sensors for geothermal well monitoring
Author(s): William Challener; Sabarni Palit; Roger Jones; Li Airey; Russell Craddock; Aaron Knobloch
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Paper Abstract

The technology for enhanced geothermal systems (EGS), in which fractures connecting deep underground wells are deliberately formed through high pressure stimulation for energy generation, is projected to enormously expand the available reserves of geothermal energy in the U.S. EGS could provide up to 100,000 MWe within the U.S. by the next 50 years. Pressure measurements, in particular, are important for determining the state of the fluid, i.e., liquid or steam, the fluid flow, and the effectiveness of the well stimulation. However, it has been especially difficult to accurately measure pressure at temperatures above ~200°C at a distance of 10 km below ground. MEMS technology has been employed for many years for extremely accurate pressure measurements through electrical readout of a MEMS fabricated resonator. By combining optical readout and drive at the end of a fiber optical cable with a MEMS resonator, it is possible to employ these highly accurate sensors within the harsh environment of a geothermal well. Sensor prototypes based on two beam and four beam resonator designs have been designed, fabricated and characterized for pressure response and accuracy. Resonant frequencies of the sensors vary between ~15 kHz and 90 kHz depending on sensor design, and laboratory measurements yielded sensitivities of frequency variation with external pressure of 0.9-2.2 Hz/psi. An opto-electronic feedback loop was designed and implemented for the field test. The sensors were packaged and deployed as part of a cable that was deployed at a geothermal well over the course of 2½ weeks. Error of the sensor versus the reference gage was 1.2% over the duration of the test. There is a high likelihood that this error is a result of hydrogen darkening of the fiber that is reducing the temperature of the resonator and, if corrected, could reduce the error to less than 0.01%.

Paper Details

Date Published: 13 March 2013
PDF: 12 pages
Proc. SPIE 8616, MOEMS and Miniaturized Systems XII, 861603 (13 March 2013); doi: 10.1117/12.2013141
Show Author Affiliations
William Challener, General Electric Global Research (United States)
Sabarni Palit, General Electric Global Research (United States)
Roger Jones, General Electric Measurement and Control (United Kingdom)
Li Airey, General Electric Measurement and Control (United Kingdom)
Russell Craddock, General Electric Measurement and Control (United Kingdom)
Aaron Knobloch, General Electric Global Research (United States)


Published in SPIE Proceedings Vol. 8616:
MOEMS and Miniaturized Systems XII
Wibool Piyawattanametha; Yong-Hwa Park, Editor(s)

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