Practical considerations for the complete 3D in situ stress estimation from convergence data using the D3 method

It is essential to understand the in situ stresses underground for engineering design and ground stability control in mining, geotechnical and petroleum engineering. Determination of the complete 3D stresses is particularly difficult due to the complex conditions underground. Overcoring and some other methods have been used in the past. They are either very expensive to implement or are based on some pre-assumptions. A recently developed alternative method is based on differential-direction drilling (D3 method). By this method, the complete 3D in situ stresses can be estimated through measurements of diametrical borehole deformation in multiple non-parallel planes. The D3 method has overcome the theoretical hurdle of using 2D data to find a 3D solution to the in situ stresses. It has five mathematical models to fit the anticipated field conditions. This paper, as a follow-up, considers practical applications of the D3 method and analyzes a few key factors which may affect its application. The minimum space angle between measurement planes and the minimum number of measurement directions in each plane (or around a borehole) are determined. The effects of measurement errors and selection of a proper model for a specific site condition are also analyzed. A statistical approach is applied to help detect erroneous measurement data and search for the best-fit solution. Practical drilling patterns in mining and petroleum engineering are also suggested.