Abstract

Although the mechanical behaviors and flow aspects of sandstone have been previously investigated, studies of the effect of the intermediate principal stress (σ2) on the strength, deformation, and permeability of sandstone are lacking. In this work, the mechanical behaviors and permeability of sandstone under true triaxial stress conditions were investigated using a newly developed true triaxial geophysical apparatus. The experimental results showed that with increasing σ2, the peak strength, octahedral effective normal stress, and octahedral effective shear stress of the sandstone increased, and the rate of increase decreased. This is because a larger intermediate principal stress coefficient b has an inhibitory effect on rock strength. In our study, as the ratio of σ2/σ3 increased, the specimen entered compressive strain in the σ2 direction during the first stress drop. The stress and strain path deviations occur during rock failure. The amount of deviation increased as the σ2 increased before the peak stress. This phenomenon indicates that elastic mechanics are not suitable for understanding this sandstone rock during its failure. The permeability evolution of the sandstone under true triaxial stress conditions was measured and analyzed to investigate the effect of σ2. During the complete true triaxial stress-strain experiments, the variation we found in gas seepage velocity could be divided into two stages. Before the first pressure drop, the gas seepage velocity was mainly affected by volume strain. After the first pressure drop, the seepage velocity was affected by the deviator strain, which can change the seepage channels.

Highlights

  • Minerals and energy are often found in deep rock formations and are generally in a complex, high-stress state

  • The results showed that rock strength and deformation are highly dependent on the stress path

  • A new multi-functional true triaxial geophysical (TTG) apparatus was self-developed by Chongqing University

Read more

Summary

Introduction

Minerals and energy are often found in deep rock formations and are generally in a complex, high-stress state. Triaxial experiments have been widely conducted to investigate the geomechanical and fluid flow behaviors of rocks under different stress conditions, which are of vital importance in evaluating the performance and efficiency of energy exploitation. Traditional triaxial experiments have been generally conducted under conventional triaxial stress (σ2 = σ3 ) conditions, ignoring the effects of σ2 on the geomechanical properties and permeability of rocks. Mogi developed the first true triaxial apparatus for rock and proposed a complete true triaxial strength criterion based on his experimental data [9,10]. Yin et al used a self-developed true triaxial apparatus to investigate the rock failure mechanism along different stress paths [20]. This work presents strength, deformation, and permeability measurements of sandstone under true triaxial stress conditions using the newly-developed, multi-functional, true triaxial geophysical (TTG) apparatus [28]. The results were used to investigate the geomechanical and fluid flow behavior of the sandstone under true triaxial stress conditions

Experimental Apparatus
Experimental
Specimen
Effect
Relationship
Effect of Intermediate on the Transport
Conclusions
Full Text
Published version (Free)

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call