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Scale Detection in Geothermal Systems The use of nuclear monitoring techniques

Scale Detection in Geothermal Systems The use of nuclear monitoring techniques E. Stamatakis a,b , T. Bjørnstad b , C. Chatzichristos b , J. Muller b and A. Stubos a a National Centre for Scientific Research Demokritos (NCSRD), Athens, Greece

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Scale Detection in Geothermal Systems The use of nuclear monitoring techniques

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  1. Scale Detection in Geothermal Systems The use of nuclear monitoring techniques E. Stamatakisa,b, T. Bjørnstadb, C. Chatzichristosb, J. Mullerb and A. Stubosa aNational Centre for Scientific Research Demokritos (NCSRD), Athens, Greece bInstitute for Energy Technology (IFE), Kjeller, Norway

  2. Outline • Nuclear experimental methods • Gamma transmission experiments • Method • Typical results • Gamma emission (tracer) experiments • Method • Typical radiotracer results

  3. Nuclear based methods • Gamma emission based on radioactive tracers added to the flowing and reacting system • Gamma transmission based on use of external gamma sources

  4. Principles of gamma transmission Absorption sample Gamma source Gamma detector Io Ix x Transmission of a mono-energetic beam of collimated photons through a simple absorption sample can be described by Lambert-Beer’s equation  is the linear mass absorption coefficient with dimension L-1 (cm-1), x the sample thickness

  5. Mass absorption coefficient A quantity more commonly found tabulated is the mass absorption coefficient/ with dimension cm2/g. In a composite sample the attenuation is additive according to XAl XCa Xl XCa XAl

  6. E (keV) Iabs(%) 80.998  0.008 34.0  0.3 276.397  0.012 7.16  0.07 302.851  0.015 18.3  0.1 356.005  0.017 62.0  0.8 383.851  0.020 8.9  0.1 133Ba The gamma source used in the present experiment is 133Ba due to suitable energies (see table below) and half-life (10.5 y). Main gamma-ray energies and intensities for 133Ba are:

  7. Experimental setup

  8. Close-up look of -ray source and detector arrangement

  9. 1 0.7 160 15 1 2 1.5 160 15 1 3-6 20 185 10 1 Preliminary lab. experiments Temp. C Pres. bar Flowr. ml/min SR RUN

  10. Results from “Run 1” Gamma attenuation measurements for calcite precipitation at the inlet of the tube at 160oC, 15 bars and SR=0.7 (run 1)

  11. Results from “Run 2” Gamma attenuation measurements for calcite precipitation at the inlet of the tube at 160oC, 15 bars and SR=1.5 (run 2)

  12. Results from “Runs 3-6” Gamma attenuation measurements for calcite precipitation in the presence and absence of a scale inhibitor 10cm from inlet of the tube at 185oC, 10 bars and SR=1.5 (runs 3-6)

  13. Calcite growth rate 0,275 0,250 Scaling rates (scale thickness as a function of time) of calcite precipitation at the inlet of the tube for run 2 - preliminary results 0,225 0,200 0,175 0,150 Scale thickness (cm) 0,125 0,100 0,075 0,050 0,025 0 0 5 10 15 20 25 Time (hour)

  14. Calcite distribution across the tube Scale thickness distribution across the tube at the end of run 3

  15. Discussion on -transmission • The 133Ba-source (30 mCi or 100 MBq) gives a typical counting rate of about 4500 cps (counts per second) in tube filled with water (ID = 10 mm) with a detector collimator opening of 4.5x4.5 mm.  • The brine-filled tube reduces the normalized incident intensity from 1.000 to 0.891when corrected for the Al-metal walls. • The increased mass thickness (g/cm2) due to scale obviously leads to an increased attenuation and to a reduction in contrast towards mass changes during the experiment. • Transmission experiments may be used to study calcite scaling in open tubes with the dimensions used here.

  16. Principles of the -emission method • CaCO3 scaling may be studied by radio-labeling of any of the chemical components involved. • However, for on-line, continuous and non-intrusive detection, gamma-ray emitters are required. • Neither O nor C have suitable gamma-ray emitting isotopes. • Ca has only one suitable radioactive isotope, namely 47Ca,with a half-life of 4.54 days.

  17. Chart of nuclides - How to produce 47Ca 21 Protons 20 19 24 25 26 27 28 29 30 Neutrons

  18. Tracer- experimental setup

  19. On-line detector setup • The main gamma energy of 47Ca is 1297 keV. However, by including also its Compton background and lower energies in the counting window, the sensitivity in the experiment may be increased. • It is necessary to avoid contribution from the 159 keV γ-quanta of the daughter radionuclide 47Sc. • The energy window for the detectors will therefore be chosen from 350 keV and upwards.

  20. Other measured parameters • Samples are also collected periodically at the exit end of the sandpack and the activity of 47Ca (1297 keV) in solution is determined in off-line high-resolution gamma-spectrometric measurements with a HpGe-detector coupled to a multichannel analyzer.  • Solution temperature Ts, differential pressure Δp, pH, absolute system pressure p and 47Ca2+ activity (counting rate R) from the two on-line detectors are logged by computer during the experiment.

  21. Typical tracer results (1) Add NaHCO3 scales 47Ca background tind Environmental background

  22. Typical tracer results (2) Typical results from a previous experiment with higher SR: 47Ca deposit growth at the inlet and Δp buildup along the tube vs. time 47Ca deposit growth in the presence and absence of a scale inhibitor

  23. Typical tracer results (3) 47Ca deposit distribution across the tube at different time-steps Final distribution of the deposits across the tube

  24. Discussion on -emission • The radiotracer 47Ca can be used to study CaCO3 precipitation in tube blocking tests providing the following unique information: • The induction time of CaCO3 scale deposition • Visualization of the spatial distribution (concentration versus position) of the CaCO3 scale deposition • All experiments with tracers showed that the tracer monitoring gives a shorter induction time than monitoring of the pressure drop • A novel technique for the determination of MIC, based on the γ-emission method, can be developed.

  25. Final Conclusions • Both methods are capable to visualize the distribution of the scale deposits, a result that is not readily obtained by methods commonly used in conventional dynamic scaling experiments. • The techniques are sensitive to scaling, resulting generally in shorter induction times compared to Δp-monitoring. • The methodologies can be easily used for the laboratory investigation of the scaling processes occurring in geological systems, including oilfield, geothermal and hydrology applications and for all kind of mineral scales. • Their results are meant to be applicable at the field scale; the quantification of the earlier occurrence of scale precipitation that those techniques attain can be directly implemented in large scale simulators.

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