Sensitivity of Results of the Water Flow Problem in a Discrete Fracture Network with Large Coefficient Differences

This work deals with modelling of groundwater flow in compact rock with network of discrete fractures. The test problem is given by stochastically generated network of lines (fractures) with large variations of the aperture, conductivity, and discretisation element size which leads to the differences of the coefficients in the linear equations system up to ten orders of magnitude. We compare our own simulation code using mixed finite elements with commercial code NAPSAC using standard finite elements. Both codes produce consistent results, with differences in percents but unevenly distributed. Results from mixed finite elements have four orders of magnitude smaller error of mass balance than those from standard finite elements.