Host: The Japan Society of Mechanical Engineers
Name : [in Japanese]
Date : September 26, 2022 - September 28, 2022
A cylindrical rock-core obtained by borehole drilling expands radially into a slightly elliptical shape along its transverse cross-section when the rock sample is relieved of its in-situ anisotropic stress by drilling. The magnitudes and orientation of in-situ stresses can, in principle, be estimated from the circumferential variation of core expansion. However, it is not possible to evaluate the expansion from a core collected in a conventional way, with a single drilling bit, since it will be in its expanded state when extracted and lacks information about its required pre-expansion dimensions. To overcome this problem, we propose an innovative way of core drilling referred to as Dual-bit Coring. This approach results in a single core that has two signature transverse cross-sections: the first has an elliptical shape resulting from core expansion and the second records the initial circular shape prior expansion. We simulated numerically the process of cutting a rock column out as a core by the Dual-bit Coring method and examined how the column deforms during core drilling.
