The Achilles' Heel of geothermal reservoir simulators

The simulation of geothermal reservoirs involves the solution of the equations describing multiphase, non-isothermal flow in porous media. These equations are highly nonlinear, particularly as the solution encounters the boundary of the two-phase region. There are essentially as many ways of accommodating this nonlinearity as there are numerical models of geothermal reservoirs. However, there is no universally accepted method for establishing the relative accuracy of these techniques. Well-established methodologies such as Fourier analysis and comparison against analytical solutions are simply not applicable to nonlinear systems. A necessary but not sufficient condition for convergence is the conservation of mass energy and momentum. This information is generally provided as an integral part of the numerical solution