A pressure-enthalpy finite element model for simulating hydrothermal reservoirs

A numerical model is presented for simulating single or two-phase flow and energy transport in hydrothermal reservoirs. The model is formulated via two non-linear equations for fluid pressure and enthalpy. Both equations are solved simultaneously using a new finite element technique which employs asymmetric weighting functions to overcome numerical oscillation. Non-linearity is treated by a modified Newton-Raphson scheme which takes into account derivative discontinuities in the non-linear coefficients. This scheme also treats unknown flux boundary conditions inplicitly, thus allowing larger time steps to be taken without inducing instability. The proposed model is applied to two test examples involving one-dimensional flow in both hot water and steam dominated reservoirs. Results indicate that the numerical technique presented is efficient and the model can be used to simulate both types of reservoirs.