Gipronikel Institute LLC, Saint Petersburg, Russia:

A. V. Trofimov, Head of the Centre, Candidate of Technical Sciences, e-mail: trofimovav@nornik.ru
A. P. Kirkin, Junior Researcher, e-mail: alexkirkin2011@gmail.com
A. E. Rumyantsev, Lead Researcher, Candidate of Technical Sciences, e-mail: rumyantsevae@nornik.ru

Gipronikel Institute LLC, Saint Petersburg, Russia¹ ; Peter the Great Saint Petersburg Polytechnic University, Saint Petersburg, Russia²:
A. V. Yavarov, Lead Researcher¹, Assistant Professor², Candidate of Technical Sciences, e-mail: yavarovav@nornik.ru

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.

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