Earth Science Frontiers ›› 2020, Vol. 27 ›› Issue (1): 112-122.DOI: 10.13745/j.esf.2020.1.13

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The application of FixAl and isotopic methods in the study of flowback fluids from Enhanced Geothermal Systems (EGS)

TIAN Jiao1,2,3(), PANG Zhonghe1,2,3,*(), ZHANG Rui4   

  1. 1. Institute of Geology and Geophysics, Chinese Academy of Sciences; Key Laboratory of Shale Gas and Geoengineering, Chinese Academy of Science, Beijing 100029, China
    2. Institutions of Earth Science, Chinese Academy of Sciences, Beijing 100029, China
    3. University of Chinese Academy of Sciences, Beijing 100049, China
    4. Menaul School Qingdao, Qingdao 266000, China
  • Received:2019-03-29 Revised:2019-08-30 Online:2020-01-20 Published:2020-01-20
  • Contact: PANG Zhonghe

Abstract:

Enhanced Geothermal Systems (EGS) is an emerging technology for exploiting the geothermal resource in hot rocks with low permeability. The flowback fluid injected into the deep reservoir to extract heat, reflects not only the physico-chemical properties of the reservoir but also efficiency of the geothermal resource exploitation. FixAl method and oxygen isotope thermometry have been used widely in natural geothermal systems. In this study, we focused on the applicability of these two methods in EGS flowback experiment. Based on flowback fluids data collected from typical EGS around the world, we evaluated chemical equilibrium states of minerals and flowback fluids and calculated underground fluids thermal exchange temperatures using FixAl method. Using isotope model we verified the mixing and displacement processes of brine. Our studies validated the usefulness of these two methods in EGS research. Moreover, we showed that the chemical characteristics of flowback fluid can be useful in determining brine content of flowback fluids, identifying dissolution of magmatic volatiles and additive residues after reservoir renovation, and predicting scaling trend or corrosiveness of fluids. Future work should focus on in-depth studies of chemical properties of flowback fluids through experiments and modeling, so as to establish a scientific evaluation model for deep geothermal resource extraction.

Key words: hot dry rock, enhanced geothermal systems, flowback fluids, chemical characteristics

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