**5. Conclusion**

*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 quasi-random lattice of nodes and springs.

The springs between the nodes break when their strength (in tension) is exceeded. Breaking of the springs corresponds to the formation of microcracks, and microcracks may link to form macrofractures. The SJM (smooth joint model) is used to represent pre-existing joints in the model. Thus, the SJM allows simulation of sliding of a pre-existing joint in the model, unaf‐ fected by the apparent surface roughness resulting from lattice resolution and random

Three-Dimensional Numerical Model of Hydraulic Fracturing in Fractured Rock Masses

http://dx.doi.org/10.5772/56313

829

The model is fully coupled hydro-mechanically. There are several ways in which fluid interacts with the rock matrix. First, fluid pressures may induce opening or sliding of the fractures. Second, mechanical deformation of fractures causes changes in joint pressures. Third, the mechanical deformation changes the permeability of the rock mass as the joint apertures

The new code is a promising tool for simulation and understanding of complex processes, including propagation of HF and its interaction with DFN, during stimulation of unconven‐

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

[1] Potyondy, D. O, & Cundall, P. A. A Bonded-Particle Model of Rock. Int. J. Rock

[2] Pierce, M. Mas Ivars D., Cundall P.A., Potyondy D.O. "A Synthetic Rock Mass Model for Jointed Rock," in Rock Mechanics: Meeting Society's Challenges and Demands (1st Canada-U.S. Rock Mechanics Symposium, Vancouver, May 2007), Fundamen‐ tals, New Technologies & New Ideas, E. Eberhardt et al., Eds. London: Taylor &

arrangement of lattice nodes.

change.

tional reservoirs.

HF Simulator.

**Author details**

**References**

B. Damjanac, C. Detournay, P.A. Cundall and Varun

Mech. & Min. Sci., (2004). , 41, 1329-1364.

Francis Group; (2007). , 1, 341-349.

Itasca Consulting Group, Inc., Minneapolis, Minnesota, USA

**Acknowledgements**

**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 springs between the nodes break when their strength (in tension) is exceeded. Breaking of the springs corresponds to the formation of microcracks, and microcracks may link to form macrofractures. The SJM (smooth joint model) is used to represent pre-existing joints in the model. Thus, the SJM allows simulation of sliding of a pre-existing joint in the model, unaf‐ fected by the apparent surface roughness resulting from lattice resolution and random arrangement of lattice nodes.

The model is fully coupled hydro-mechanically. There are several ways in which fluid interacts with the rock matrix. First, fluid pressures may induce opening or sliding of the fractures. Second, mechanical deformation of fractures causes changes in joint pressures. Third, the mechanical deformation changes the permeability of the rock mass as the joint apertures change.

The new code is a promising tool for simulation and understanding of complex processes, including propagation of HF and its interaction with DFN, during stimulation of unconven‐ tional reservoirs.
