The Effect of Quantity and Spacings of Notches on Hydraulic Fracturing at Different Stress Regimes

Abstract

ABSTRACT Due to the increased understanding of mining techniques previously uneconomical larger orebodies are becoming viable and block caves are increasingly common. One such technological advance is the use of Hydraulic Fracturing. With the majority of research for hydraulic fracturing being focused on reservoir development, a need to better understand how this translates into mining is required. Exploring how fractures initiate, grow, and the influence of notch spacings and density, more knowledge is gained around prescribing fractures to the mining industry and environments needs. By using multiple perforations, due to coalescing of fractures, more complex fracturing could be through the change in localized stresses. To understand the influence of fracture density, lab work was undertaken looking at how density of notches and notch spacing influence the fracture growth, breakdown pressure, and propagation pressures in Adelaide Black Granite under two different stress regimes. The results show that location of notches has minimal impact on pressures but create changes in the fracture direction. This work confirms that with multiple notches this technique can be used to change fracture propagation. providing solid foundation for designing campaigns with multiple simultaneous injections, and fractures density within the mining industry. INTRODUCTION Block caving is gaining traction as a viable method of mining within hard rock mining environments. As easy shallow depth orebodies are becoming rare and scarcer, then methods to extract deeper orebodies safely has become a need of the industry. Block caving has an initially high outlay of costs and slow turn around in producing tons relative to Sub Level Caving methods, but in the long term requires less active development and low running costs alongside the ability to design footprints to meet the needs of the stresses, structures and environments, it equates to an economically sound, customizable, and relatively simple mining method. The challenges faced with the block cave mining method, and future caves that are established at depths are mostly related to the higher stress environment and cave propagation and stalling. A way to mitigate these risks is through the use of hydraulic fracturing. By inducing fractures in a favorable manner into the environment stress can be redistributed, highly stressed zones can be activated, and competent rocks weakened for the promotion of cave growth