Taiyuan Ligong Daxue xuebao (Mar 2024)
Study on Shear Failure Characteristics of Oil Shale under High-temperature Steam Treatment
Abstract
Purposes In the process of in-situ steam-assisted oil shale extraction, the shear strength of oil shale plays a crucial role in the stability of injection and production wells as well as the mining gallery. Additionally, the shear strength of rock formation is influenced by temperature. The variations in the shear characteristics of oil shale under different temperatures and shear angles are investigated. Methods A steam generation apparatus was employed to heat the oil shale. In the experimental setup, steam temperatures were set at 100, 200, 300, 400, and 500 ℃, separately. Subsequently, the steam-treated oil shale was subjected to variable-angle shear experiments at shear angles of 45°, 55°, and 65°. According to the experiment results, the variable-angle shear parameters and peak shear strain of the oil shale were calculated. Furthermore, an analysis of the shear failure characteristics of the oil shale following exposure to different steam conditions was conducted. Findings The research findings can be summarized as follows: 1) At steam temperatures below 300 ℃, oil shale exhibits pronounced brittle failure characteristics, while at temperatures of 400 ℃ and 500 ℃, ductile failure characteristics becomes more evident; 2) The cohesion of oil shale first increases and then decreases with the increase of steam temperature. Similarly, the internal friction angle decreases initially with rising steam temperature, followed by an increase. The shear strength decreases as the shear angle increases; 3) The peak shear strain of the oil shale increases with steam temperature rising, and high shear angle has a significant impact on the peak shear strain of the rock; 4) The shear failure mode of the oil shale transitions from penetrating failure to combined failure with an increase in steam temperature, along with an increase in secondary cracks.
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