**Abstract**

Last year, a joint Mining and Oil & Gas industry consortium was established in Canada to conduct hydraulic fracturing (HF) tests accompanied by a mine-back of fractured regions to assess HF models and microseismic monitoring data during controlled experiments. Details about the displacement field, fracture aperture and extent, and micro-seismic parameters could then be verified and used as calibration data for modeling of HF processes in igneous and dense sedimentary rocks.

Various injection experiments are planned and they will include pre-fracturing rock mass characterisation using best available current techniques, dense arrays of multi-parameter wall and borehole-mounted instruments, and the treated volume will be mined through to assess fracturing effectiveness, existing fractures and new fracture interactions, and to deter‐ mine if pathways can be identified for improving currently available numerical and fracture network modeling tools.

In this paper we present the results of the experimental design and planning phase, outlin‐ ing objectives and justifications for planned experimental layouts. Preliminary plans for a first mine-through trial at Newcrest Mining's Cadia East mine in New South Wales, Austral‐ ia are described. The hypotheses advanced in this experimental design, supported by evi‐ dence from the literature, are that activation and development of a fracture network by hydraulic stimulation is possible if the injection procedure is designed such that injection pressures and rates are maintained within an optimal window, thereby producing condi‐ tions under which effective stress management for risk mitigation in deep mining can best

© 2013 Kaiser et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

be achieved. The evaluation of these hypotheses is the focus of the current high level experi‐ mental plan presented in the paper.

based on experiments permitting near-field monitoring followed by investigation of the

Hydraulic Fracturing Mine Back Trials — Design Rationale and Project Status

http://dx.doi.org/10.5772/56260

879

Various hydraulic fracturing (HF) experiments have been undertaken in mines, some with mine-through experiments (e.g. [6]) for various purposes: to better understand fracture propagation, fracture interaction with natural joints, fragmentation changes, penetration of proppants, etc. Successes have been reported with respect to the use of HF for rock mass preconditioning, for rock fragmentation and cave initiation (e.g. [2]) but unanswered questions remain about its effectiveness in affecting stress redistribution and in controlling energy release from critically stressed rock mass structures. There are much anecdotal but little scientifically proven evidence that HF can help manage stresses, or not. The authors suggest that it may be the methodology of fracturing that may be the source of the apparent contra‐ dictions reported in the literature. As mines progress to greater depth stress management for the control of seismically releasable energy becomes of strategic importance. Furthermore, with the introduction of mechanized excavation techniques for rapid mine development (e.g., by Rio Tinto, AngloGold Ashanti, and others), new risks related to strain-bursting are

introduced because of the less-damaging nature of these excavation techniques.

For the mining sector the motivations are to broaden the application of hydraulic fracturing and rock mass stimulation beyond cave initiation, propagation and fragmentation manage‐ ment by introducing methodologies for hydraulic stress and rock mass stiffness management that will eventually find introduction for risk mitigation in deep and high stress mining operations. In particular, the problem of fault-slip rockbursting is perplexing and, it is thought, can possibly be addressed through the creation of "damage zones" around potentially unstable structures, thereby reducing the energy emission levels and rates and improving constructa‐

It is hypothesised that current hydraulic injection techniques deployed in cave mine applica‐ tions are predominantly propagating hydraulic fractures and that shear dilation is a secondary process. Indeed, opening Mode I fractures develop within a narrow (almost planar) zone normal to σ3, and their irregular nature promotes asperity locking resulting in little final net shear strength or stiffness reduction. It is recognised that as fluids are lost in the rock mass surrounding the hydraulic fracture some distributed shearing of critically oriented natural fractures will also occur (e.g. [3]), however in order to enable stress management, one must promote volumetrically distributed irreversible changes to the rock mass and the development of injection techniques that achieve this objective is at the core of the planned research. Section 3 presents the output of a review of current injection practices for various applications and their effect on the rock mass. It served as background for the development of the experimental

treated volume via mapping and monitoring during mine-through.

**2.1. Mining perspective**

bility in highly stressed ground.

approach presented in Section 4.

**Keywords** stress management, stiffness modification, shale gas analogue, mine-back experi‐ ments, model calibration, hydraulic fracture, naturally fractured rocks
