1. Date of download: 6/26/2016 Copyright © ASME. All rights reserved. From: Numerical Simulation of Complex Fracture Network Development by Hydraulic Fracturing in Naturally Fractured Ultratight Formations J. Energy Resour. Technol. 2014;136(4):042905-042905-9. doi:10.1115/1.4028690 Overview of the main parameters and processes involved in the hydraulic fracturing simulations (graphics taken from Refs. [1–3]) Figure Legend:

2. Date of download: 6/26/2016 Copyright © ASME. All rights reserved. From: Numerical Simulation of Complex Fracture Network Development by Hydraulic Fracturing in Naturally Fractured Ultratight Formations J. Energy Resour. Technol. 2014;136(4):042905-042905-9. doi:10.1115/1.4028690 Critical stress for fracture propagation [17] Figure Legend:

3. Date of download: 6/26/2016 Copyright © ASME. All rights reserved. From: Numerical Simulation of Complex Fracture Network Development by Hydraulic Fracturing in Naturally Fractured Ultratight Formations J. Energy Resour. Technol. 2014;136(4):042905-042905-9. doi:10.1115/1.4028690 Schematic top view of the base case scenario (two fracture sets, σ h = σ H, and 25 m fracture spacing). The primary vertical fracture set is parallel to σ H. The secondary vertical fracture set is perpendicular to the primary fracture set. Figure Legend:

4. Date of download: 6/26/2016 Copyright © ASME. All rights reserved. From: Numerical Simulation of Complex Fracture Network Development by Hydraulic Fracturing in Naturally Fractured Ultratight Formations J. Energy Resour. Technol. 2014;136(4):042905-042905-9. doi:10.1115/1.4028690 The influence of the stress variation with depth for a 2.5 km deep shale and a 5 km deep granite (1: constant stress, 2: linear stress increase, 3: stepwise stress increase, and 4: low stress formation) Figure Legend:

5. Date of download: 6/26/2016 Copyright © ASME. All rights reserved. From: Numerical Simulation of Complex Fracture Network Development by Hydraulic Fracturing in Naturally Fractured Ultratight Formations J. Energy Resour. Technol. 2014;136(4):042905-042905-9. doi:10.1115/1.4028690 Influence of the distance between injection point and the lower stress barrier on the minimum stress contrast needed for confinement and the minimum formation height (if no upper stress barrier is present) Figure Legend:

6. Date of download: 6/26/2016 Copyright © ASME. All rights reserved. From: Numerical Simulation of Complex Fracture Network Development by Hydraulic Fracturing in Naturally Fractured Ultratight Formations J. Energy Resour. Technol. 2014;136(4):042905-042905-9. doi:10.1115/1.4028690 Minimum stress contrast needed to confine fracture height growth for different fracture spacings, fracture sets, and rock types Figure Legend:

7. Date of download: 6/26/2016 Copyright © ASME. All rights reserved. From: Numerical Simulation of Complex Fracture Network Development by Hydraulic Fracturing in Naturally Fractured Ultratight Formations J. Energy Resour. Technol. 2014;136(4):042905-042905-9. doi:10.1115/1.4028690 Influence of the differences between vertical and minimum horizontal stress and between maximum and minimum horizontal stress on the minimum stress contrast required to confine fracture height growth Figure Legend:

8. Date of download: 6/26/2016 Copyright © ASME. All rights reserved. From: Numerical Simulation of Complex Fracture Network Development by Hydraulic Fracturing in Naturally Fractured Ultratight Formations J. Energy Resour. Technol. 2014;136(4):042905-042905-9. doi:10.1115/1.4028690 Influence of the fracture spacing on the maximum net pressure observed during stimulation for different rock types and fracture sets Figure Legend:

9. Date of download: 6/26/2016 Copyright © ASME. All rights reserved. From: Numerical Simulation of Complex Fracture Network Development by Hydraulic Fracturing in Naturally Fractured Ultratight Formations J. Energy Resour. Technol. 2014;136(4):042905-042905-9. doi:10.1115/1.4028690 Influence of the differences between the three principle stresses on the maximum net pressure observed during stimulation for different rock types and fracture sets Figure Legend:

10. Date of download: 6/26/2016 Copyright © ASME. All rights reserved. From: Numerical Simulation of Complex Fracture Network Development by Hydraulic Fracturing in Naturally Fractured Ultratight Formations J. Energy Resour. Technol. 2014;136(4):042905-042905-9. doi:10.1115/1.4028690 Influence of fracture spacing on the total area of the DFN for different rock types and fracture sets Figure Legend:

11. Date of download: 6/26/2016 Copyright © ASME. All rights reserved. From: Numerical Simulation of Complex Fracture Network Development by Hydraulic Fracturing in Naturally Fractured Ultratight Formations J. Energy Resour. Technol. 2014;136(4):042905-042905-9. doi:10.1115/1.4028690 Influence of the differences between the three principle stresses on the total area of the DFN for different rock types and fracture sets Figure Legend:

12. Date of download: 6/26/2016 Copyright © ASME. All rights reserved. From: Numerical Simulation of Complex Fracture Network Development by Hydraulic Fracturing in Naturally Fractured Ultratight Formations J. Energy Resour. Technol. 2014;136(4):042905-042905-9. doi:10.1115/1.4028690 Influence of the differences between the three principle stresses on the aspect ratio of the fracture system for different rock types and fracture sets Figure Legend: