Real-time computerized tomography (CT) experiments on sandstone damage evolution during triaxial compression with chemical corrosion

Feng, Xia‐Ting; Chen, Sili; Zhou, Hui

doi:10.1016/s1365-1609(03)00059-5

Cited by 207 publications

(60 citation statements)

References 11 publications

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“…In the past, in situ imaging of experiments based on CT technologies was applied to a wide range of studies including geomechanical behavior of fractures (Re and Scavia, 1999), evaluations of triaxial tests (Feng et al, 2004;Ge et al, 2001;Lenoir et al, 2007;Ren and Ge, 2004;Vinegar et al, 1991;Zhou et al, 2008), shear tests (Tatone and Grasselli, 2015), sand production experiments (Santos et al, 2010) as well as various single-/multi-phase core-flooding experiments in fractured and unfractured rocks (Huo and Benson, 2015;Krevor et al, 2012;Oh et al, 2013;Perrin and Benson, 2010;Pini and Benson, 2013;Pini et al, 2012;Rangel-German et al, 2006;Schembre and Kovscek, 2003;Shi et al, 2009;Watanabe et al, 2011). CT technology generally represents a 3-D non-destructive method to image material contrasts in high resolution and, therefore, is well suited to reproduce dynamic processes in situ and in "real time".…”

Section: Introductionmentioning

confidence: 99%

Simulating stress-dependent fluid flow in a fractured core sample using real-time X-ray CT data

et al. 2016

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Abstract. Various geoscientific applications require a fast prediction of fracture permeability for an optimal workflow. Hence, the objective of the current study is to introduce and validate a practical method to characterize and approximate single flow in fractures under different stress conditions by using a core-flooding apparatus, in situ X-ray computed tomography (CT) scans and a finite-volume method solving the Navier-Stokes-Brinkman equations. The permeability of the fractured sandstone sample was measured stepwise during a loading-unloading cycle (0.7 to 22.1 MPa and back) to validate the numerical results. Simultaneously, the pressurized core sample was imaged with a medical X-ray CT scanner with a voxel dimension of 0.5 × 0.5 × 1.0 mm 3 . Fracture geometries were obtained by CT images based on a modification of the simplified missing attenuation (MSMA) approach. Simulation results revealed both qualitative plausibility and a quantitative approximation of the experimentally derived permeabilities. The qualitative results indicate flow channeling along several preferential flow paths with less pronounced tortuosity. Significant changes in permeability can be assigned to temporal and permanent changes within the fracture due to applied stresses. The deviations of the quantitative results appear to be mainly caused by both local underestimation of hydraulic properties due to compositional matrix heterogeneities and the low CT resolution affecting the accurate capturing of sub-grid-scale features. Both affect the proper reproduction of the actual connectivity and therefore also the depiction of the expected permeability hysteresis. Furthermore, the threshold value CT mat (1862.6 HU) depicting the matrix material represents the most sensitive input parameter of the simulations. Small variations of CT mat can cause enormous changes in simulated permeability by up to a factor of 2.6 ± 0.1 and, thus, have to be defined with caution. Nevertheless, comparison with further CT-based flow simulations indicates that the proposed method represents a valuable method to approximate actual permeabilities, particularly for smooth fractures (< 35 µm). However, further systematic investigations concerning the applicability of the method are essential for future studies. Thus, some recommendations are compiled by also including suggestions of comparable studies.

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Section: Introductionmentioning

confidence: 99%

Simulating stress-dependent fluid flow in a fractured core sample using real-time X-ray CT data

et al. 2016

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“…Furthermore, they also analyzed the shear band using X-ray computerized tomography (CT) and scanning electron microscopy (SEM). Feng et al (2004) studied the damage evolution of sandstone under triaxial compression with chemical corrosion using real-time X-ray CT. They surmised that the CT value is the most important parameter describing the damage evolution process of rock.…”

Section: Introductionmentioning

confidence: 99%

Experimental Investigation on the Strength, Deformability, Failure Behavior and Acoustic Emission Locations of Red Sandstone Under Triaxial Compression

2012

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Conventional triaxial compression and ''reducing confining pressure'' experiments were carried out for red sandstone by an MTS815 Flex Test GT rock mechanics experimental system. Our results show that the post-peak axial deformation characteristics of red sandstone changed as the confining pressure was increased from 5 to 65 MPa. Young's modulus of red sandstone increased nonlinearly with increasing confining pressure, but Poisson's ratio remained unaffected. Using our new data, the compactive and dilatant behavior, strength and failure characteristics of sandstone under triaxial compression are further discussed. For our data, the nonlinear Hoek-Brown criterion better reflects the peak strength properties than the linear MohrCoulomb criterion. However, the residual strength shows a clear linear relationship with confining pressure, which can be best described using the linear Mohr-Coulomb criterion. The peak and residual strengths were not directly related to the two different loading paths. The onset of dilatancy (C 0 ), the switch from compaction-dominated to dilatant-dominated behavior (D 0 ) and the stress at zero volumetric strain all increased linearly with the confining pressure. In our conventional triaxial compression experiments, the failure mode changed from mixed tension and shear fracture (single shear fracture) to shear fracture with double slippage planes with increasing confining pressure. However, the failure mode in our ''reducing confining pressure'' experiments was more complicated and results mainly from the unstable failure characteristics of the rock during the reduction in confining pressure. Finally, based on our acoustic emission (AE) locations, at a confining pressure of 35 MPa, a detailed analysis of the evolutionary process of internal cracks is presented for the entire loading process.

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“…However, it is interesting to note that the average Young's modulus of the 25% brine saturated samples is about the same as that of 5% brine saturated samples, which indicates that the variation of Young's modulus under brine saturation may follow a parabolic fashion with the increase of NaCl concentration. This is due to the chemical corrosive nature of brine solutions as indicated by Feng et al [37]. The corrosive effect of the NaCl ions may improve the plasticization of the coal during the interaction between the ions and the coal mass and this corrosive effect is more significant when samples are soaked with high NaCl concentration solutions.…”

Section: Moisture Content Effect On Young's Modulusmentioning

confidence: 98%

Effects of Water and Brine Saturation on Mechanical Property Alterations of Brown Coal

et al. 2018

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Abstract:The adsorption of moisture or brine into coal causes the coal mass mechanical properties to be significantly altered, which can greatly affect the coal mining and coal seam gas extraction process. A study was therefore initiated to investigate the influence of moisture and brine saturations (5-25%) on brown coals' strength through a series of unconfined compressive strength tests, with the aid of acoustic emission, optical 3-D deformation analysis and scanning electron microscopy. According to the results, the coal mass is weakened by up to 26% upon the adsorption of moisture and water saturated samples show no crack propagation, whereas brine saturation enhances coal strength by up to 21% and delays crack propagation due to the crystallization of sodium chloride. Besides, a high brine concentration (25%) greatly improves coal mass strength but impairs the increase of Young's modulus due to its corrosive nature, which is consistent with the values of maximum strain at failure of the tested samples (3.9%, 3.1% and 3.6% for 5%, 15% and 25% brine saturated samples, respectively). In addition, because of the precipitation of sodium chloride in coal and the increase of conductivity of pore fluid, more acoustic emission signals are detected for brine saturated samples, while water saturated samples exhibit mush less acoustic release compared to the unsaturated samples.

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Real-time computerized tomography (CT) experiments on sandstone damage evolution during triaxial compression with chemical corrosion

Cited by 207 publications

References 11 publications

Simulating stress-dependent fluid flow in a fractured core sample using real-time X-ray CT data

Simulating stress-dependent fluid flow in a fractured core sample using real-time X-ray CT data

Experimental Investigation on the Strength, Deformability, Failure Behavior and Acoustic Emission Locations of Red Sandstone Under Triaxial Compression

Effects of Water and Brine Saturation on Mechanical Property Alterations of Brown Coal

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