The desirable and undesirable effects on stress reconstruction using the deformation rate analysis (DRA).

The Deformation Rate Analysis (DRA) utilizes the stress-strain curves obtained from uniaxial tests on rock samples to reconstruct the in-situ stress the rock was subjected to. The approach to this test is to measure the strain difference between two completed load-unload cycles under uniaxial compression. The method has been used since 2002 to undertake in situ stress tensor determinations. In general, the method uses oriented diamond drill core obtained for exploration purposes. The strain difference can be as small as a few microstrains, hence an imperfect lest environment could easily vary the reading of strain and as a consequence the result can be difficult to interpret or is misleading. Another potential issue associated with the DRA method can be attributed to the rock properties. Because the sample was originally in a confined environment (underground), it expands after the core has been extracted. The amount of expansion (open/movement of pre-existing cracks, interfaces, and grain boundaries) in a core is likely to be nonuniform along whole core. When applying a load to the sample, “crushing of asperities at crack inner surface“ occurs during the process of crack closure and it creates unwanted inelastic strain which can mask the indicator of the in situ stress. This compaction effect can be observed using acoustic sensors and observation of the stress-strain curve, and it is less pronounced in the lateral strain difference.

In this paper we addressed some of the issues with undertaking the tests and completing the interpretation of the results. A suggested method of conducting a test for DRA analysis is presented in an appendix. We provide some simple solutions to improve the test condition and examine the reliability of test. Examples of the compaction effect are shown and the suggested approach when dealing with this type of result is demonstrated. The “bad“ result is discussed and compared with “good“ result. The aim is to improve or reject the result which is unsatisfactory for stress reconstruction purposes.