Stress is a critical consideration in any underground mine. Traditional techniques for measuring stress are so expensive and time consuming, many mines have extremely limited stress measurements. KORE's stress inversion technology extracts information about stress orientation and relative magnitude from borehole breakout data collected in multiple deviated boreholes using Acoustic Televiewer borehole logging technology. This means a borehole drilled for any reason (exploration, definition, geotechnical etc.) can be used to measure stress orientation, quickly and inexpensively.
An acoustic televiewer obtains a high resolution, oriented acoustic image of a borehole wall, transmitting ultrasonic pulses. These pulses reflect off the borehole wall and back to the receiver, where the amplitude of the returned signal and the travel time are recorded. Any fractures/joints or breakouts in the borehole increase the time for the pulse to travel back, reflected in the travel time log, and the relative amplitude of the pulse will be attenuated, reflected in the amplitude log.
The stress inversion is set up as a forward modelling optimization problem. Optimization is done to find the stress state that best matches the observations of borehole breakout and the forward modelling calculates the theoretical orientation of breakout given some stress state.
An extensive Monte Carlo uncertainty analysis is conducted to assess the final stress model. The result is a global stress model, important for mine planning. The stress model is easily updated as mining moves into new areas or as the stress state changes.