The Utility of Threshold Reactive Tracers for Characterizing Temperature Distributions in Geothermal Reservoirs
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The Utility of Threshold Reactive Tracers for Characterizing Temperature Distributions in Geothermal Reservoirs Morgan Ames · Kewen Li · Roland Horne
Received: 19 July 2013 / Accepted: 4 November 2013 © International Association for Mathematical Geosciences 2013
Abstract Reactive tracers have long been investigated as a means to measure geothermal temperature profiles and predict thermal breakthrough, but this method has only been used in practice to estimate an effective (or average) reservoir temperature. This means that spatial information about the temperature profile is lost, and a sequence of reactive tracer tests would need to be carried out at different times to track the thermal front. Advances in nanotechnology have made the use of nanoparticles as geothermal tracers feasible. Nanomaterials can be designed with a high degree of control over their response to temperature, which could enable them to provide more information than reactive solute tracers. Nanoreactors that prevent reaction of encapsulated reactants from occurring until a threshold temperature is reached are a promising candidate for use as geothermal temperature sensors. It is demonstrated through modeling that this could enable engineers to determine the location of temperature measurements to map the inter-well temperature profile at a given time. This could facilitate more accurate reservoir fracture geometry characterization and thermal breakthrough prediction. Keywords Tracers · Nanomaterials · Temperature threshold · Thermal breakthrough prediction
1 Introduction Thermal breakthrough prediction is a significant problem in geothermal reservoirs where reinjection is practiced. Reinjection of fluids is an inherent part of the Enhanced Geothermal Systems (EGS) concept because, by definition, these reservoirs
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M. Ames ( ) · K. Li · R. Horne Department of Energy Resources Engineering, Stanford University, 367 Panama Street, Green Earth Sciences 065, Stanford, CA 94305, USA e-mail: [email protected]
Math Geosci
do not have fluid in place. Reinjection is also practiced in most conventional hydrothermal reservoirs. The ability to predict thermal breakthrough accurately in advance would facilitate educated reservoir management decisions to alter injection and production strategies in order to increase profitability. A number of researchers have proposed the use of reactive solute tracers with temperature-dependent reaction rates to measure reservoir temperature (Robinson et al. 1984; Tester et al. 1986; Rose and Adams 1994). The basic idea is that the reaction rate increases exponentially with temperature, so a tracer test performed at the beginning of reservoir life would result in more conversion of the reactive tracer than a test performed after significant cooling. Thus, by comparing the return curves from the two reactive tracer tests, it would be possible to estimate the extent of reservoir cooling and hopefully predict thermal breakthrough far in advance. Behrens et al. (2009) reported that the return curves of reactive tracers w
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