Constraining the state of stress from stress-induced borehole failure and drill core samples

Purpose and goal

The pre-study aims at: 1. Constraining the state of stress using stress-induced features (SIFs) and laboratory core data from 1.0-1.8 km depth in the LKAB mine in Malmberget; a depth interval where employment of traditional stress measurement techniques are starting to be are hampered. 2. Study of geological features in the rock mass and geochemistry to understand how these features affect the strength properties of the rock. 3. If possible, initiate a full-scale innovation project for estimation of the state of stress using SIFs and core data.

Expected results and effects

One objective within the project is to implement and further develop a cost-effective method to estimate the state of stress at larger depths using televiewer, core, and geochemical data. Interestingly, the proposed methodology predict a stress field in quite good agreement with the hydraulic stress data. However, one outcome of the analysis proved that the methodology is sensitive to a series of parameters. A sensitivity analysis is required to increase reliability and more field data would significantly reduce the uncertainty of the methodology (primarily in situ pore pressure).

Planned approach and implementation

The pre-study has ben undertaken by C. Wanhainen, M. Ask, D. Ask, and T. Bauer. We have completed three stages: 1.Literature study 2.Interpretation of stress-induced fetures using existing acoustic televiewer, core data and have made additional geochemical laboratory tests. 3.An existing theory for interpretation of borehole breakouts and drilling-induced fractures have been employed, allowing estimates of the state of stress. We will in the near future discuss our findings with LKAB, at first hand, and propose a full scale project.