Taghipoor, S & Hosseini, N 2024, 'In situ principal stress measurement using minifrac testing and borehole breakout analysis in the south range rocks of the Sudbury Basin, Canada', in P Andrieux & D Cumming-Potvin (eds), Deep Mining 2024: Proceedings of the 10th International Conference on Deep and High Stress Mining, pp. 1207-1218, https://doi.org/10.36487/ACG_repo/2465_79
(https://papers.acg.uwa.edu.au/p/2465_79_Taghipoor/)
Abstract: KGHM’s Victoria project is in the south range of the Sudbury Basin in Ontario, Canada. The deposit includes mineralisation zones of nickel, copper and precious metals (platinum, palladium and gold).
As a part of geomechanical data collection for mine design, a series of minifrac tests were conducted in a vertical borehole (shaft’s pilot hole) at the Victoria project. The minifrac tests were conducted in the exploration’s shaft pilot hole at depths of between 350 to 750 m. The minifrac test results and the observed borehole breakouts at depth were used to estimate the magnitude and orientation of the in situ principal stresses and correlate them to depth. The magnitude and orientation of the minimum, intermediate and maximum principal stresses were estimated using the test data. It is shown in this paper how each of these principal stresses is spatially orientated and how their magnitudes vary with depth. 
The minimum principal stress is expected to be sub-vertical. The intermediate and the maximum principal stresses are expected to be sub-horizontal. The kH ratio is estimated to approach 2.8 at a depth of 350 m and to substantially vary with depth, approaching 1.5 at 700 m. Below 700 m, change in the kH ratio becomes minimal and remains constant at 1.45. The intermediate principal stress shows a similar trend with depth. The kh ratio starts at 1.94 at 350 m, approaches 1.02 at 700 m and reaches a plateau of 1 at a depth below that. The estimated magnitudes of the in situ principal stresses will also be compared with the previous measurements conducted by other mine operators in the Sudbury Basin.

Keywords: in situ stress measurement, minifrac testing, borehole breakout, Sudbury Basin