Petroleum-based downhole geophysical methods for subsurface characterisation: a case study from Cadia East mine

Authors: Galybin, KA; Viegas, G; Tennant, D; Lewis, D

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DOI https://doi.org/10.36487/ACG_repo/2205_87

Cite As:
Galybin, KA, Viegas, G, Tennant, D & Lewis, D 2022, 'Petroleum-based downhole geophysical methods for subsurface characterisation: a case study from Cadia East mine', in Y Potvin (ed.), Caving 2022: Proceedings of the Fifth International Conference on Block and Sublevel Caving, Australian Centre for Geomechanics, Perth, pp. 1255-1264, https://doi.org/10.36487/ACG_repo/2205_87

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Abstract:
Subsurface characterisation in underground mining is often limited to interpretation of drillhole cored data and surface geophysical data, later aided by geological mapping of limited underground development. Due to the large volume and increasing depth of orebodies in block cave mining, subsurface characterisation is increasingly reliant on 3D modelling from spatial sampled core data. This paper presents a case study from the Cadia East block cave mine, where a series of petroleum-inspired techniques were used to: (i) enhance subsurface characterisation with continuous imaging at depth; and (ii) to decrease the risks associated with interpretation of sparse geophysical data. A comprehensive suite of wireline logging was acquired in one drillhole and included full bore formation micro-imager, sonic logging and vertical seismic profiling (VSP). The formation micro-imager data were used to identify the fault and fractures that cross the wellbore. These data were also used in conjunction with sonic data to generate a 1D Mechanical Earth Model (MEM) as well as a high resolution Unconfined Compressive Strength (UCS) profile. In addition to the drillhole-centric characterisation, VSP measurements extended the characterisation away from the wellbore. The VSP acquisition comprised two source locations allowing measurement of compressional, shear velocities and attenuation as well as seismic imaging of the eastern end of the orebody. The short VSP-derived 2D seismic line showed presence of several geological structures, further validated with the integration of the micro-imager data. This added a significant amount of confidence to the structural/geotechnical model. It is envisaged that through the application of petroleum-based geophysical methods, additional information can be obtained such that geotechnical hazards are incorporated into long-term mine planning as early as possible.

Keywords: Cadia East Mine, vertical seismic profiling, formation micro-imager

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