| Abstract |
In geothermal process, the fluid is often boiling or near boiling, and the flow may be either a two phase flow with a varying liquid saturation or a near boiling liquid which flashes to steam. This presents a substantial potential for geothermal hazards including steam kick or blowout in geothermal drilling and hydrothermal outburst in mining. However, previous works focus on the simulation of long-term geothermal process with phase change, the fast water-steam transient is less understood due to its high nonlinearity. In this paper, based on pressure and enthalpy, the governing equations in the form of coupled nonlinear partial differential equations are formulated for describing multiphase flow in porous media. The IAPWS Industry Formulation 1997 formulation is used here to calculate water-steam thermodynamic properties and its derivatives in terms of pressure and enthalpy. A Newton-Raphson based nonlinear finite element technique is applied to solve the coupled highly nonlinear equations. Sudden changes of pressure and temperature in the geothermal process is simulated to address how water-steam transient is initiated. In addition, several important parameters, such as intrinsic permeability, porosity, rock density and rock heat capacity, which influence two phase fluid and heat flow in porous media are analyzed. The pressure, temperature, enthalpy and water saturation profiles are compared to figure out the controlling factor of fast water-steam transient behavior. Results from this numerical simulation work are helpful to understand the water-steam transient behavior in geothermal process, and it also has guiding significance for geothermal hazards prediction. |