Technical Committee Reservoir Engineering

Numerical Investigations of Frac-Propagation in Tight Gas Reservoirs by use of FDM-Program FLAC3D

In the framework of DGMK research project 680-1, the FDM-Program FLAC3D which is common in scientific field of Rock Mechanics was used for the simulation of Fracpropagation in a real geo-model, based on data of a North German Rotliegend tight gas reservoir. This reservoir was treated hydraulically by a massive fracturing in 1983. The results regarding the fracture propagation were compared to those of the analytical P3D simulator FracPro.

It was noticed that the original code FLAC3D, based on the Continuum Mechanics, was unsuitable for field applications. In further investigations, an own developed algorithm with a changing boundary condition on the basis of Discontinuum Mechanics was implemented in FLAC3D. The results showed a relative good agreement with those of FracPro.

The advantages of this new computing algorithm are above all the ability to optimize multifracs as well as to simulate realistically a flexible and irregular fracture front, which in turn reflects the stress states in multi-layers and their different rock mechanical properties. The performed sensibility analysis showed that the fracture geometry is strongly dependent on the viscosity of fracturing fluid, while the injection rate and the tensile strength of rock mass have a much lower influence.