Operator-based Linearization for Modeling of Low-enthalpy Geothermal Processes

Simulation of geothermal processes is based on the solution of strongly nonlinear governing equations describing flow of mass and energy in the subsurface. The solution of this problem requires a linearization of governing equations. Recently, a new approach based on the operator-based multi-linear representation of conservation equations was proposed for an isothermal flow and transport. The discretized version of conservation equations was transformed to the operator form where each term of the equation was represented as a product of two operators: one dependent on physical properties of fluids (e.g. density or viscosity) and another dependent on properties, altered in space (e.g. porosity or permeability). The first type of operators was parametrized in the physical space of the simulation problem at the pre-processing stage, or adaptively during the course of simulation. Next, multi-linear interpolation was applied for physics-based operators when the linearization of the second type of operators was performed in a conventional manner. In this work, the approach has been extended for the thermal processes. The operator-based parametrization was performed using temperature, pressure and composition. The performance and robustness of the method was tested against the conventional approach on low enthalpy models of geothermal reservoirs of practical interest.