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EOS7Energy Efficiency Calculation

I want to perform cyclic injection and extraction to obtain energy efficiency. I have set the energy efficiency using the following calculation formula. However, when I set MOP(5) greater than 0, the enthalpy values of all units also appear, which are different from the ENTHALPY given in the output. Which enthalpy value should I use as the basis for calculating energy efficiency? Below are the attached result files for injection and extraction. I hope to receive assistance and greatly appreciate it.
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3 replies

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    • Reservoir Engineer
    • Alfredo_b
    • 11 days ago
    • Reported - view

    You have to use the enthalpy printed in the output file related to the sinks and sources contributing to the cyclic injection and extraction process ypu want to monitor.

    The enthalpy printed using MOP(5) is that of the phases present in each element of the discretization grid  (see pag. 13 of TOUGH2 user's guide), not the enthalpy of fluid produced or injected.

    Regards,

    Alfredo

      • bronze_rose
      • 10 days ago
      • Reported - view

       Thank you for your response. I performed injection followed by extraction with equal injection and extraction volumes. For each well grid, there was 12 hours of injection at 0.9 kg/s and two extraction phases of 3 hours each at 1.8 kg/s. In theory, the energy efficiency for the first cycle should be above 90%. However, based on the output files from the extraction phase, the extracted heat is significantly less than the injected heat, only around 70%. Additionally, as the cycles continue, my energy efficiency actually increases. Could there be an issue with my TOUGH2 configuration? This problem has been troubling me for a long time, and I hope to receive your advice. I have attached my input and output files, along with some screenshots of the output files for your review.  
      Wishing you good health and happiness.imageimage

      injection.out extraction1.out extraction2.out INCON INFILE MESH
    • Reservoir Engineer
    • Alfredo_b
    • 10 days ago
    • Reported - view

    Sorry, but I have no time to run your input file. I can just make some comments looking at the shared files.

    - you sent separate output files for the daily air injection step and the two daily extraction steps. I would have expected a single input file to simulate many daily cycles with injection and extraction history given through a table under GENER.

    - during extraction, the brine phase mass fraction amounts to 2-6 %, while I guess it would be better to have just the extraction of (wet) air with the brine phase at irreducible saturation around the wells. Looking at some published papers about CAES (Compressed Air Energy Storage), at the beginning air is injected to create an air bubble around the injection wells with water at irreducible saturation in such a way that subsequent cycling injection/extraction does not produce liquid brine (apart for possible condensation of water vapor).

    - you mention CAES in your TOUGH2 files. In Compressed Air Energy Storage in aquifers (CAESA) the energy of compressed air is recovered by expanding the compressed air in a turbine. Thus, the evaluation of energy storage efficiency is a bit more complex than just an enthalpy balance. You may have a look at:  Oldenburg and Pan (2013). Porous Media Compressed Air Energy Storage (PM-CAES): Theory and Simulation of the Coupled Wellbore-Reservoir System. TPM volume 97, p. 201–221.

    - whitout an initial gas bubble, I guess the energy efficiency of CAES cannot be constant even with constant extraction/injection flow rates as it will be affected by evolving conditions in the reservoir volume affected by air injection with evolving spatial distibution of T and saturations.  

    - you should consider that in EOS7 the internal energy of gaseous air is evaluated assuming an ideal gas approach. So, JT effects upon compression and decompression of air are not simulated. Depending on P changes, these effects may not be completely negligible. Other thermophysical properties in EOS7 are computed with an approximated approach whose accuracy depend on P, T and salinity ranges.

    Others, with specific experience on CAES modeling, may give you further and more useful advices.

    Regards,

    Alfredo

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