BOX 5.1
Oil and Gas Production

Optical systems are increasingly being used by the oil and gas industry as a means for monitoring wells, allowing increased production, and mitigating risks. Industry adoption of optics has been relatively recent, as the high pressure and temperature conditions in a well reduce the lifetime of conventional fiber optics to be substantially shorter than the 20 years over which most wells are expected to produce. Since 2000, fiber-based distributed temperature sensors have become common tools for monitoring the performance of wells, and have proven to be a robust source of information about the well performance.

Distributed temperature sensors rely on the fiber locally changing temperature and scattering light back up the fiber owing to the temperature change. Thus, when combined with a pulsed laser source, the backscattered light allows a temperature profile of the well to be determined. The temperature of the fiber is changed locally owing to fluids flowing into the well bore (Joule-Thomson effect). This information is combined with geothermal models to accurately locate and quantify fluid flows in the well.

More recently, fiber systems have been deployed for distributed acoustic sensing (DAS), to monitor well activity during several phases of well completion. DAS uses a principle similar to that for distributed temperature sensors, but uses acoustic waves generated from within the well to alter the refractive index of the fiber probe. The backscattered radiation from this index variation can be collected and processed to discriminate between various sources and depths. These systems offer reliable discrimination between perforation clusters that are active during the acid injection stage and those that are taking most of the proppant throughout the job. This technology also shows promise for many other functions, such as sand detection and gas breakthrough detection.

SOURCES: Algeroy, J., J. Lovell, G. Tirado, R. Meyyappan, G. Brown, R. Greenaway, M. Carney, J. Meyer, J. Davies, and I. Pinzon. 2010. Permanent monitoring: Taking it to the reservoir. Oilfield Review 22(1):34-41; Molenaar, M., D. Hill, P. Webster, E. Fidan, and B. Birch. 2011. “First Downhole Application of Distributed Acoustic Sensing (DAS) for Hydraulic Fracturing Monitoring and Diagnostics.” Society of Petroleum Engineers Hydraulic Fracturing Technology Conference, January 24-26, 2011, The Woodlands, Tex.

to non-concentrating systems. With CPV, higher-cost, and more efficient, solar cells can be used. The cost of the concentrators will be the main issue, as stated in the NAS-NAE-NRC report Overview and Summary of America’s Energy Future: Technology and Transformation published in 2010: “In general, nearly all of the costs involved in using renewable energy for power generation are associated with the manufacturing and installation of the equipment.”7 For high-concentration CPV, more concentrating options are available for larger electric plants, and so CPV may favor utility-scale plants over the smaller plants used by an individual. Photosynthesis is also briefly discussed below as another method of capturing light from the Sun and turning it into energy. However, it is clear that a successful deployment of

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7 NAS-NAE-NRC. 2010. Overview and Summary of America’s Energy Future, p. 22.



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