**Acknowledgements**

**5. Conclusion**

828 Effective and Sustainable Hydraulic Fracturing

quasi-random lattice of nodes and springs.

*HF Simulator* is a powerful 3D simulator for hydraulic fracturing in jointed rock mass that allows the main mechanisms (nonlinear mechanical response, fluid flow in joints and coupled fluid-mechanical interaction) to be reproduced. The formulation of *HF Simulator* is based on a

**Figure 7.** Hydraulic fractures generated in a homogeneous medium (dark blue disks are microcracks)

**Figure 8.** Hydraulic fractures generated in a medium with three pre-existing joints (blue disks are microcracks)

The development of the numerical code described in this paper was funded by BP America. The authors would like to thank BP America for their support. Matt Purvance, Jim Hazzard and Maurilio Torres of Itasca Consulting Group, Inc. are thanked for their valuable work on HF Simulator.
