Recent developments in energy exploration at depths of 5000 to 25,000 feet have made it necessary to quickly and reliably determine the in-situ stresses acting on the wellbore.

Differential Strain Analysis (DSA) is being investigated as a technique applied to core samples to indirectly determine the in-situ stress state.

Testing is being pursued in three steps. First, field measurements of strain are made in-situ as the core is pulled out of the well. Second, the cores are brought to the lab and DSA is performed under in-situ hydrostatic conditions. Third, the rock is examined microscopically.

These tests have been performed on both oriented and non-oriented cores from Texas, Louisiana and Fennsylvania.

At this point in the investigation, it appears very favorable that a reasonably accurate estimate of the 3-dimensional stress state can be obtained using the strain curve analysis method. It has been demonstrated mathematically that not only the ratio of the stresses can be derived but also the orientation of the stresses in free space. The application of these equations to the data from the latest high quality runs yields result well within the reproducible tolerance of other methods.

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