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Computer Modelling of Gas and Liquid Tracers in Geothermal Reservoirs

Computer Modelling of Gas and Liquid Tracers in Geothermal Reservoirs. Mark Trew Colin Harvey. Michael O’Sullivan Errol Anderson. Karsten Pruess. Introduction. Scope and aim of research Gas and liquid tracers Partitioning models

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Computer Modelling of Gas and Liquid Tracers in Geothermal Reservoirs

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  1. Computer Modelling of Gas and Liquid Tracers in Geothermal Reservoirs Mark Trew Colin Harvey Michael O’Sullivan Errol Anderson Karsten Pruess

  2. 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. A partitioning model for gas tracers Liquid mass fraction (Henry’s Law): independent variable Harvey empirical correlation of Henry’s constant Vapor mass fraction: calculated assuming ideal gas behavior: calculated from a standard empirical correlation

  4. 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. A partitioning model for gas tracers - application Linear least-squares fit of Harvey function to gas distribution coefficient regression data SF6 R-12 R-123

  6. A partitioning model for liquid tracers Liquid mass fraction: independent variable mass fractionmole fraction Vapor mole fraction: calculated from a standard empirical correlation activity coefficient; calculated from the Wilson model

  7. 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. A partitioning model for liquid tracers - Wilson’s model Activity coefficients for a multi-component mixture (using binary interaction parameters):

  9. A partitioning model for liquid tracers - application methanol Wilson models of the molar excess Gibbs free energy n-propanol

  10. Compressed liquid Superheated vapor Two-phase mixture Implementing partitioning models in TOUGH2 Sequence of calculations in the TOUGH2 equation of state (EOS): 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 Calculate thermodynamic properties of components Determine phase state Independent variables for each phase state:

  11. 200ºC Qualitative results - test problem • Isotropic reservoir: 1 km3, f = 0.1, k = 10-14 m2 • Two-phase convective fluid flow • 3374 computational blocks • 100 kg of each tracer injected for 20 minutes into central region Steady-state solution 10% vapor saturation

  12. Qualitative results - gas tracers SF6 R-12 R-123 Following injection 100 days

  13. Qualitative results - liquid tracers Tritiated water Methanol n-Propanol Following injection 100 days

  14. 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. Acknowledgements • Mike Adams (EGI Utah) • JAPEX Geoscience Institute

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