A stress calculation model for the 3D borehole slotter

A stress calculation model is proposed for a new stress measurement device called the 3D borehole slotter. This instrument allows the calculation of the 3D in situ stress tensor in a single borehole without the need for a drill on the site at the time of the measurement and without bonding strain gauges at the borehole wall. The 3D borehole slotter requires cutting half moon shaped slots with different orientations at a borehole wall using a small diamond impregnated blade and monitoring the strains which are relieved normal to the slot. This paper shows that combining six slots cut on the borehole wall with one to three slots cut parallel to the borehole axis and five to three cut with a 45° angle, allows the calculation of the in situ stress tensor. The optimal slot combination is determined and 3D finite element analyses are used to evaluate the degree of stress relief normal to the slot at the strain sensor location and also to estimate the strains induced parallel to the slot by this local stress relief. The results obtained from these analyses are then used directly in the stress calculation model.