**6. Conclusions**

For the range of injection pressures equal to the hydraulic fracturing pressure:

**•** Greater injection rates result in a smaller shear stimulated surface area. The results indicate that once the HF is formed, the increase in the injection rates will not be favourable for shear

Total affected surface area

Shear stimulated surface area

HF Surface Area

(c)

(d)

(e)

**Figure 12.** Effect of elevated injection rates, history of quantitative indices.

Average HF Aperture

Average DFN Aperture

**•** Smaller injection rates result in a greater total affected surface area; and

(a)

(b)

stimulation.

284 Effective and Sustainable Hydraulic Fracturing

The response of pre-existing fracture networks, typically encountered in geothermal reservoirs and shale gas formations, to fluid injection, including potential HF propagation, has been studied numerically. This is the first in a proposed series of studies intended to obtain a better understanding of the complex processes involved in DFN stimulation and hydraulic fracturing by fluid injection.

The sensitivity of the models with respect to various in-situ and operational parameters has been evaluated. The results are summarized as follows:


### **Acknowledgements**

The authors acknowledge the financial support of Sandia National Laboratories for this project.
