Experimental and Numerical Study on the Mechanical Evolution of Shizhu Shale under Water-rock Interaction
Abstract
To investigate the mechanical degradation characteristics and underlying mechanisms of Shizhu shale under water-rock interaction, this study combines laboratory experiments with numerical simulations. Shale specimens are immersed in field-produced water for 0, 1, 3, 7, 15, and 30 days, followed by X-ray diffraction (XRD) mineralogical analysis, Brazilian tensile tests, and triaxial compression tests. Based on the finite- discrete element method (FDEM), a numerical model incorporating mineralogical evolution is established to verify and analyze the influence mechanisms of mineral components on the mechanical behavior of shale. XRD results indicate that under flowback fluid immersion, carbonate minerals such as dolomite and calcite exhibit pronounced fluctuations characterized by a dynamic dissolution - precipitation process, whereas quartz shows strong chemical inertness and clay minerals (illite) display only minor variations. The mechanical properties ofshale show a pronounced time - dependent evolution. The Brazilian tensile strength exhibits a fluctuating trend of slight decrease - recovery - slight decrease, while the triaxial compressive strength evolves through three stages: strengthening (0 - 3 days), degradation (7 - 15 days), and restabilization (15 - 30 days). The peak compressive strength increasesfrom an initial value of 346.54 MPa to 402.99 MPa at 3 days, decreases to 164.27 MPa at 7 days, and finally stabilizes at 174. 22 MPa at 30 days. Failure patterns evolve with soaking time, which is closely coupled with mineralogical variation and microstructural reconstruction. The established FDEM model reproduces the mechanical responses and failure patterns of shale, confirming that the macroscopic mechanical behavior of shale results from a dynamic balance between the strengthening effects of hard minerals (dolomite and quartz) and the weakening effects of soft minerals (illite and calcite). This study can provide theoretical references for integrity assessment and risk control of underground oil and natural gasstorage.
Article type: Research article
Cited as:
Li B, Zhu YJ, Li YZ, et al. 2026. Experimental and Numerical Study on the Mechanical Evolution of Shizhu Shale under Water-rock Interaction. GeoStorage, 2(1), 78-97.
DOI:
https://doi.org/10.46690/gs.2026.01.06Keywords:
Shale, water-rock interaction, mechanical properties, mineral composition, fractal dimensionReferences
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