Use of numerical modelling to determine optimum overcoring parameters in rock stress-strain state analysis

Abstract

Before a mineral deposit can be developed deeper, a geomechanical survey should be carried out to determine the stress tensor of the rock mass. The most common in situ stress measurement techniques include the methods of hydraulic fracturing and overcoring. Each of them has its advantages and its drawbacks. The authors of this paper propose to conduct two stages of numerical modelling in order to enhance the efficiency of measurements performed by overcoring method. The first stage involves building a model of drilling to determine the optimum drilling depth. At the second stage, a core drilling model is built. Absolute transverse strains have been determined in reference points of a pilot borehole at each stage of core drilling. The created simulation models help choose the drilling depth of coaxial boreholes, estimate the potential growth of plastic strains that cause core destruction, define the amount of overdrilling to be done to coaxial boreholes and determine the optimum location for the measurement tools. The developed models can also be used to determine stresses by inverse problem solving.