Geomechanical Characterization of Marcellus Shale

Understanding the reservoir conditions and material properties that govern the geomechanical behavior of shale formations under in situ conditions is of vital importance for many geomechanical applications. The development of new numerical codes and advanced multi-physical (thermo-hydro-chemo-mechanical) constitutive models has led to an increasing demand for fundamental material property data. Previous studies have shown that deformational rock properties are not single-value, well-defined, linear parameters. This paper reports on an experimental program that explores geomechanical properties of Marcellus Shale through a series of isotropic compression (i.e. σ ₁ = σ ₂ = σ ₃) and triaxial (i.e. σ ₁ > σ ₂ = σ ₃) experiments. Deformational and failure response of these rocks, as well as anisotropy evolution, were studied under different stress and temperature conditions using single- and multi-stage triaxial tests. Laboratory results revealed significant nonlinear and pressure-dependent mechanical response as a consequence of the rock fabric and the occurrence of microcracks in these shales. Moreover, multi-stage triaxial tests proved to be useful tools for obtaining failure envelopes using a single specimen. Furthermore, the anisotropic nature of Marcellus Shale was successfully characterized using a three-parameter coupled model.