**Appendix 2**

DAFSAM15 proposes to reduce significantly this limitation by conducting research in deep mines that are unique laboratories for full-scale analysis of seismogenic processes. The mines provide a 'missing link' that bridges between the failure of simple and small samples in laboratory experiments, and earthquakes along complex and large faults in the crust. There is no practical way to conduct such analyses in other environment. To unravel the complexity of earthquake processes, this project is designed as integrated multidisciplinary studies of specialists from seismology, structural geology, mining and rock engineering, geophysics, rock mechanics, geochemistry and geobiology. The scientific objectives of the project are the characterization of near-field behavior of active faults before, during and after earthquakes". 16See also http://www.iris.edu/hq/instrumentation\_meeting/files/pdfs/IRIS\_Johnston.pdf

Petroleum engineers can now reach depths in excess of 6 km and have developed advanced drilling control technologies that allow precise access to locations extending horizontally to

*Minimally invasive extraction*

These and related developments are stimulating interest in application of borehole technolo‐ gies to other areas of subsurface engineering, including the development of less-invasive mining technologies, i.e., borehole extraction of minerals. Some applications, e.g., where crystalline rocks are involved, are contingent on the development of significantly lower-cost drilling technologies. The critical dependence of society on reliable and economic subsurface

*Adapt petroleum technology – in harder rock. Drilling!*

> *Schematic of Directional Drilling from off-shore oil*

*The red borehole is guided remotely to stay within the center of a narrow (ca 4m) producing horizon for several* 

*platforms .* 

*kilometers*

more than 10-15 km from a single vertical hole (see Figure 2).

74 Effective and Sustainable Hydraulic Fracturing

**Figure A1-2.** Schematic illustration of directional drilling for petroleum production.

15 DAFSAM -Drilling Active Faults in South African Mines. 16 http://www.icdp-online.org/front\_content.php?idcat=460

#### **Effect of coring in pre-stressed rock**

The consequences of disturbing a pre-stressed rock medium are illustrated by examining the rock coring operation. Figure A2-1 shows the stress concentrations in a rock core in a brittle

**Figure A-2.1.** Tensile stress concentrations induced in a brittle rock during coring.

rock. If the in-situ stress normal to the axis of drilling is sufficiently high tensile cracks can develop in the core. Where lateral stresses are very high, then tensile 'spalling' may result, as shown in the photograph of the bottom right of Figure A2-1. Where the rock is more 'ductile' the core may undergo permanent deformation without fracturing. In both cases, the mechan‐ ical properties of these cores may differ significantly from those of the rock in situ from which the core was obtained.

[5] Calo, M, Dorbath, C, Cornet, F. H, & Cuenot, N. (2011). Large scale aseismic motion identified through 4D P-wave tomography; Geophys. J. Int. , 186, 1295-1314.

Fractures and Fracturing: Hydraulic Fracturing in Jointed Rock

http://dx.doi.org/10.5772/56366

77

[6] Cundall, P. A. (2008). An Approach to Rock Mass Modelling," in From Rock Mass to Rock Model-CD Workshop Presentations (15 September, 2008)- SHIRMS 2008 (Proc. 1st Southern Hemisphere International Rock Symposium, Perth, Western Australia, September 2008) Y. Potvin et al., Eds. Nedlands, Western Australia: Australian Cen‐

[7] Cladouhos, T. T, Clyne, M, Nichols, M, Petty, S, Osborn, W. L, & Nofziger, L. (2011). Newberry Volcano EGS Demonstration Stimulation Modeling" GRC Transactions, ,

[8] Cornet, F. H. (2012). The relationship between seismic and aseismic motions induced

[9] Cornet, F. H, & Röckel, T. (2012). Vertical stress profiles and the significance of

[10] Cundall, P. A, & Pierce, M. E. and D. Mas Ivars. ((2008). Quantifying the Size Effect

[11] Damjanac, B, & Fairhurst, C. (2010). Evidence for a Long-Term Strength Threshold in

[12] Damjanac, B, Detournay, C, & Cundall, P. A. and Varun, ((2013). Three-Dimensional Numerical Model of Hydraulic Fracturing in Fractured Rock Masses" Proc. HF The International Conference for Effective and Sustainable Hydraulic Fracturing, Bris‐

[13] Damjanac, B, & Fairhurst, C. Evidence for a Long-Term Strength Threshold in Crys‐ talline Rock,‖ Rock Mech. Rock Eng., 43, 513-531 ((2010). Duchane, D and D. Brown, (2002) "Hot Dry Rock (HDR) Geothermal Energy Research and Development at Fen‐ ton Hill, New Mexico" GHC (Geo-Heat Center) Bulletin, December. 2002 , 13-19. [14] Fairhurst, C, & Carranza-torres, C. (2002). Closing the Circle- Some Comments on Design Procedures for Tunnel Supports in Rock," in Proceedings of the University of Minnesota 50th Annual Geotechnical Conference (February 2002), J. F. Labuz and J. G. Bentler, Eds. Minneapolis: University of Minnesota, 2002. [available at www.itas‐

[15] Fairhurst, C. (1971). Fundamental Considerations Relating to the Strength of Rock. Colloquium on Rock Fracture, Ruhr University, Bochum, Germany, April 1971. (see http://www.itascacg.com/about/ff.php)Revised and published in Report of the Work‐ shop on Extreme Ground Motions at Yucca Mountain, August 23-25, 2004, U.S. Geo‐ logical Survey, USGS Open-File Report T. C. Hanks et al., Eds. Reston, Virginia:

by forced fluid injections." Hydrogeology Journal (2012) 20: 1463-1466

"stress decoupling". Tectonophysics , 581(2012), 193-205.

of Rock Mass Strength" in SHIRMS 2008 (op.cit.) , 2, 3-15.

cacg.comgo to 'About'and Fairhurst Files], 21-84.

Crystalline Rock,‖ Rock Mech. Rock Eng., 43, 513-531 (2010).

tre for Geomechanics.

bane, May 20-22, 2013, 2013.

USGS, 2006., 2006-1277.

35, 317-322.
