PSI - Issue 6

A. Martemyanov et al. / Procedia Structural Integrity 6 (2017) 292–300 Martemyanov Andrey et al// Structural Integrity Procedia 00 (2017) 000 – 000

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a high content of organic carbon, which weight content in some intervals reaches 20%. Macroscopic lithological description of core samples, analysis of petrographic sections and data of scanning electron microscopy demonstrate that rocks in the anisotropy intervals have pronounced layering at various scales. Figure 2 has an example of calcareous-siliceous strongly carbonaceous rock from the upper part of the Bajen formation. At the macroscopic level, stratification along the axis of the sample drilled parallel to the bedding is visible. According to the petrographic analysis of the section, together with mineralogy data, the rock is a kerogen carbonate-siliceous rhythm with a thin horizontal schist microstructure. Mechanical tests carried out on core samples made it possible to determine the values of 5 elastic moduli (namely: Young's moduli parallel and perpendicular to the bedding, Poisson's coefficients parallel and perpendicular to the bedding, and the shear modulus perpendicular to the bedding [5]) needed to describe the transversely isotropic medium. These elastic modules were determined from series of hydrostatic loading, zero-radial strain loading, and pseudotrexial compression tests on samples drilled parallel, perpendicular, and at an angle of 45 degrees to bedding. This results showed that for rocks from the anisotropic interval of the Bajen horizon, the ratio of dynamic and static Young's moduli parallel and perpendicular to the bedding lies in the range 1.3-2.5. Note that a similar relationship between stratification and anisotropy of elastic properties is also noted for shale rocks in North America [6].

Figure 2. Left: core sample after a multi-stage pseudo-triaxial compression test. In the center: petrographic section, made of the same sample. Right: an appropriate photo of SEM.

Simultaneously, a series of carried out tests made it possible to establish anisotropy of strength characteristics within a given interval. Following the work [9], the dependence of the UCS on the bedding stratum of the rock was obtained.

Figure 3. Compressive strength measurements for samples made at different angles

As a result of Sonic Scanner data interpretation curves of horizontal and vertical dynamic Young's modulus and Poisson's ratio were obtained. Transition from dynamic elastic properties to static made with the help of correlation