A two-phase geothermal wellbore simulator to model THC behavior using Elmer-PHREEQC

Abstract

The thermohydraulic-chemical (THC) behavior of a deep geothermal wellbore can be seriously affected by two-phase flow effect. In geothermal wellbore with high non-condensable gas content applications, this situation may lead to inaccurate pressure, temperature, and mineral saturation index calculation. However, due to the complexity of describing this effect, it is normally not considered in the modeling process. A method for calculating the transport and (de)pressurization with a thermal load of a two-phase multi-component geothermal fluid is presented. The thermodynamical and transport properties for an H2O - salt (NaCl, CaCl2, KCl, MgCl2, NaHCO3) - gas (CO2, N2, CH4, H2S) mixture are calculated using the fugacity-activity, three-zone Equation of State. The fluid flow is described by a heterogeneous drift-flux model, which is solved using the Elmer FEM. An operator splitting algorithm is applied to couple PHREEQC for calculating chemical reaction. Numerical results are shown, illustrating the effect of mixture composition and the feasibility of the approach.