Abstract
Pore gas has a significant influence on rock strength. This study performed triaxial compression tests of gas-infiltrated sandy shale samples to investigate the strength characteristics under gas pressures of 0 and 2 MPa. The effective stress coefficient was evaluated while considering the gas and solid coupling effect, and was found to decrease with increasing confining pressure. The calculated and different assumed coefficient values (0 and 1) were applied to obtain the effective principal stress. The experimental results would serve as fundamental strength data for fitting analysis in failure criterion work. The Mohr-Coulomb, Hoek-Brown, Drucker-Prager, linear Mogi, and non-linear Mogi criteria were modified based on the effective stress principle of porous rock. In addition, the RMSE, cohesion, and internal friction angle were utilized for a quantitative criterion comparison. The results showed that the Mohr-Coulomb, Drucker-Prager, and linear Mogi failure criteria led to higher errors, whereas the Hoek-Brown criterion gave an apparent distortion as a result of the empirical strength parameters. Moreover, the non-linear Mogi criterion showed a good fit. The predicted strength was overestimated when α = 0 and underestimated when α = 1, with a more accurate strength estimated when the effective stress coefficient was calculated using the effective stress principle.
Highlights
Shale gas is an important source of clean energy and has already attracted much attention.The permeability, deformation, and strength are of great importance in the development and utilization of shale gas
The Drucker-Prager failure criterion was established on the assumption that the yield of the rock is completely determined by the second invariant of the stress deviator tensor, and it took into consideration the effect of the intermediate principal stress on the rock strength [56]
The results showed that pore methane has a certain influence on the decrease of rock strength
Summary
Shale gas is an important source of clean energy and has already attracted much attention. Associating the effect of the confining pressure with the traditional Mohr-Coulomb failure criterion, a modified non-linear failure criterion was proposed for a fitting analysis of the triaxial and polyaxial strength of intact rock and jointed rock [15,16,17]. Performed tests on the mechanical properties of rock under true triaxial stress conditions, and the strength criterion was investigated on the basis of laboratory data for Westerly granite and KTB amphibolite [25]. Triaxial compression tests were conducted to understand the effect of the pore gas pressure on the strength property and failure behaviour of sandy shale specimens. Based on the effective stress principle of porous rock, the Mohr-Coulomb, Hoek-Brown, Drucker-Prager, linear Mogi, and non-linear Mogi criteria were modified, and the criteria application with the strength data was compared and analyzed
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