Stress shadowing effects during hydraulic fracturing in block caving operations

Authors: Mejia, C; Azad, E; Roehl, D; Vallejos, JA; Rojas, E

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DOI https://doi.org/10.36487/ACG_repo/2205_84

Cite As:
Mejia, C, Azad, E, Roehl, D, Vallejos, JA & Rojas, E 2022, 'Stress shadowing effects during hydraulic fracturing in block caving operations', in Y Potvin (ed.), Caving 2022: Proceedings of the Fifth International Conference on Block and Sublevel Caving, Australian Centre for Geomechanics, Perth, pp. 1211-1226, https://doi.org/10.36487/ACG_repo/2205_84

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Abstract:
The hydraulic fracturing (HF) technique is mainly used to precondition the orebody before mining in the block caving extraction method. Weakening the rock mass to enhance its caveability, reduce seismic risks and reduce fragment sizes are the primary objectives of HF in mining. HF is used mainly in large-scale deep underground mines with low-grade metal orebodies. In this paper, hydraulic fracturing simulation is conducted based on the finite element method to study the effect of simultaneous and sequential multiple hydraulic fracturing schemes. The input and in situ data used for this simulation come from the El Teniente porphyry Cu-Mo mine. The fracture propagation is modelled with the cohesive elements using a traction-separation law. Comparing 3D and axisymmetric analysis, the similarity between fracture propagation shape and crack length prompted us to adopt axisymmetric analyses with reduced computational cost. Scenarios of simultaneous and sequential operations were analysed to consider the stress shadow effect, an understandable consequence of deformation during hydraulic fracturing. This comparison determined the fracture aperture, pore pressure, stress, and crack length. Due to the stress shadowing effect, different fracture lengths are observed. In addition, sequential injections have a subtler effect than simultaneous injections.

Keywords: hydraulic fracturing, stress shadowing effect, cohesive element, hydro-mechanical coupling, block caving

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