Anisotropic elastic, strength, and fracture properties of Marcellus shale

Abstract

Shale, a fine-grained sedimentary rock, is the key source rock for many of the world's most important oil and natural gas deposits. A deep understanding of the mechanical properties of shale is of vital importance in various geotechnical applications, including oil and gas exploitation. In this work, deformability, strength, and fracturing properties of Marcellus shale were investigated through an experimental study. Firstly, uniaxial compression, direct tension, and Brazilian tests were performed on the Marcellus shale specimens in various bedding plane orientations with respect to loading directions to measure the static mechanical properties and their anisotropy. Furthermore, the deformability of Marcellus shale was also studied through seismic velocity measurements for comparison with the static measurements. The experimental results revealed that the transversely isotropic model is applicable for describing the elastic behaviors of Marcellus shale in pure tension and compression. The elastic properties measured from these two experiments, however, were not exactly the same. Strength results showed that differences exist between splitting (Brazilian) and direct tensile strengths, both of which varied with bedding plane orientations and loading directions and were associated with different failure modes. Finally, a series of threepoint-bending tests were conducted on specimens of increasing size in three different principal notch orientations to investigate the fracture properties of the material. It was found that there exists a significant size effect on the fracture properties calculated from the measured peak loads and by using the Linear Elastic Fracture Mechanics (LEFM) theory. The fracture properties can be uniquely identified, however, by using Bažant's Size Effect Law and they were found to be anisotropic.

Experimental Study on the Difference of Shale Mechanical Properties

“…Wang et al [18] concluded that the maximum shear strength of shale is 60°based on the experimental data. rough the Brazilian split test and threepoint bending test, Jin et al [19] discussed the anisotropy of shale fracture behavior. Tang and Wu [20] gave the anisotropic crack evolution characteristics of shale and mudstone in laboratory experiments.…”

Micro- and Macroscale Consequences of Interactions between CO2 and Shale Rocks

“…Shales show two types of anisotropy: intrinsic (lithological anisotropy, developed from the preferred orientation of platy clay minerals and the development of thin lamination) and stress-induced anisotropy (anisotropy developed with an increase in stress). There are many articles in the literature discussing strength anisotropy (e.g., Jin et al [73], Fjaer and Nes [74]), where the variation of the strength of the rocks with the angle creates problems, especially in inclined wells (e.g., borehole stability). Few researchers have discussed the effects of stiffness, strength, acoustic velocity, and even fracture anisotropy on CO 2 storage or seal integrity.…”

Geomaterials Evaluation: A New Application of Ashby Plots

“…Different kinds of rocks are plotted in the chart with each kind of rock in a group. The data of 146 specimens used in the chart are all from the literature [19][20][21][22][23][24][25], in which the Young's modulus and the tensile strength are derived from laboratory experiments. Rocks towards the top right have a high value of strength and elasticity and therefore can sustain a higher value of stress.…”