1. University of Auckland New Zealand Geothermal Group Department of Engineering Science Computer Modelling of Gas and Liquid Tracers in Geothermal Reservoirs Mark Trew Colin Harvey Michael O’Sullivan Errol Anderson Karsten Pruess

2. University of Auckland New Zealand Geothermal Group Department of Engineering Science Introduction Scope and aim of research Gas and liquid tracers Partitioning models –Gas tracers: Henry’s Law and the Harvey (1996) correlation for Henry’s constants –Liquid tracers: Wilson’s model of the molar excess Gibbs energy Implementation in TOUGH2 Test problem

3. University of Auckland New Zealand Geothermal Group Department of Engineering Science A partitioning model for gas tracers independent variable Harvey empirical correlation of Henry’s constant calculated assuming ideal gas behavior: calculated from a standard empirical correlation Liquid mass fraction (Henry’s Law): Vapor mass fraction:

4. University of Auckland New Zealand Geothermal Group Department of Engineering Science A partitioning model for gas tracers - Harvey correlation Harvey (1996) empirical correlation of Henry’s constant for the entire temperature range: Sample data from gas distribution coefficient: regression of gas distribution coefficient

5. University of Auckland New Zealand Geothermal Group Department of Engineering Science A partitioning model for gas tracers - application SF 6 R-12R-123 Linear least-squares fit of Harvey function to gas distribution coefficient regression data

6. University of Auckland New Zealand Geothermal Group Department of Engineering Science A partitioning model for liquid tracers independent variable calculated from a standard empirical correlation Liquid mass fraction: Vapor mole fraction: activity coefficient; calculated from the Wilson model mass fraction  mole fraction

7. University of Auckland New Zealand Geothermal Group Department of Engineering Science A partitioning model for liquid tracers - Wilson’s model Molar excess Gibbs free energy: Wilson’s binary mixture two-parameter model: binary interaction parameters

8. University of Auckland New Zealand Geothermal Group Department of Engineering Science A partitioning model for liquid tracers - Wilson’s model Activity coefficients for a multi-component mixture (using binary interaction parameters):

9. University of Auckland New Zealand Geothermal Group Department of Engineering Science A partitioning model for liquid tracers - application Wilson models of the molar excess Gibbs free energy n-propanol methanol

10. University of Auckland New Zealand Geothermal Group Department of Engineering Science Implementing partitioning models in TOUGH2 Mass fraction calculations: (1) gas tracers in liquid phase (2) gas tracers in vapor phase (3) water in liquid phase (4) water/liquid tracers in vapor phase Compressed liquidSuperheated vaporTwo-phase mixture Determine phase state Calculate thermodynamic properties of components Sequence of calculations in the TOUGH2 equation of state (EOS): Independent variables for each phase state:

11. University of Auckland New Zealand Geothermal Group Department of Engineering Science Qualitative results - test problem Isotropic reservoir: 1 km 3,  = 0.1, k = 10 -14 m 2 Two-phase convective fluid flow 200ºC 10% vapor saturation 3374 computational blocks 100 kg of each tracer injected for 20 minutes into central region Steady-state solution

12. University of Auckland New Zealand Geothermal Group Department of Engineering Science Qualitative results - gas tracers SF 6 R-12 Following injection 100 days R-123

13. University of Auckland New Zealand Geothermal Group Department of Engineering Science Qualitative results - liquid tracers Tritiated waterMethanol Following injection 100 days n-Propanol

14. University of Auckland New Zealand Geothermal Group Department of Engineering Science Summary and conclusions Partitioning models have been developed for gas and liquid tracers The models have been implemented in a TOUGH2 equation of state Qualitative test results show the predictive and interpretative value of the models Further work: –determine mixture values for more tracers –continue to test models by matching recorded tracer returns

15. University of Auckland New Zealand Geothermal Group Department of Engineering Science Acknowledgements Mike Adams (EGI Utah) JAPEX Geoscience Institute