A 2-D numerical method for tracking a moving water table

Abstract

A new numerical method has been incorporated into the existing TOUGH2 framework to allow for more accurate tracking of a moving water table in a non-isothermal system. The method is based on the calculation of the mass flow into or out of the top surface of the model (the water table surface). The correct position of the water table is one where fluid is no longer moving into or out of the top surface of the water table block. This paper describes a numerical scheme for accurately tracking the movement of the water table. It is implemented through python scripting without interfering with the TOUGH2 code. To demonstrate the method a 2-D non-isothermal model representing a shallow reservoir with constant fluid production is considered. For comparison, an equivalent air/water EOS model was run using standard TOUGH2. The results demonstrate the improvement the new method holds over current approaches of either using a fixed water table or using an air/water model and moving the water table block by block. Further development and extension of the method will be explored in order to extend water table tracking to boiling flow and to include the vadose zone.