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| 1 | Discrete element modeling on the crack evolution behavior of brittle sandstone containing three fissures under uniaxial compression显示文摘Based on experimental results of brittle, intact sandstone under uniaxial compression, the micro-parameters were firstly confirmed by adopting particle flow code(PFC2D). Then, the validation of the simulated models were cross checked with the experimental results of brittle sandstone containing three parallel fissures under uniaxial compression. The simulated results agreed very well with the experimental results, including the peak strength, peak axial strain, and ultimate failure mode. Using the same microparameters, the numerical models containing a new geometry of three fissures are constructed to investigate the fissure angle on the fracture mechanical behavior of brittle sandstone under uniaxial compression. The strength and deformation parameters of brittle sandstone containing new three fissures are dependent to the fissure angle. With the increase of the fissure angle, the elastic modulus, the crack damage threshold,and the peak strength of brittle sandstone containing three fissures firstly increase and secondly decrease. But the peak axial strain is nonlinearly related to the fissure angle. In the entire process of deformation, the crack initiation and propagation behavior of brittle sandstone containing three fissures under uniaxial compression are investigated with respect tothe fissure angle. Six different crack coalescence modes are identified for brittle sandstone containing three fissures under uniaxial compression. The influence of the fissure angle on the length of crack propagation and crack coalescence stress is evaluated. These investigated conclusions are very important for ensuring the stability and safety of rock engineering with intermittent structures. | Sheng-Qi Yang Yan-Hua Huang P.G.Ranjith Yu-Yong Jiao Jian Ji | 2015 | Acta Mechanica Sinica2015，31，6： | 11 |
| 2 | Crushing and embedment of proppant packs under cyclic loading: An insight to enhanced unconventional oil/gas recovery显示文摘Crushing and embedment are two critical downhole proppant degradation mechanisms that lead to a significant drop in production outputs in unconventional oil/gas stimulation projects. These persistent production drops due to the non-linear responses of proppants under reservoir conditions put the future utilization of such advanced stimulation techniques in unconventional energy extraction in doubt. The aim of this study is to address these issues by conducting a comprehensive experimental approach. According to the results, whatever the type of proppant, all proppant packs tend to undergo significant plastic deformation under the first loading cycle.Moreover, the utilization of ceramic proppants(which retain proppant pack porosity up to 75%), larger proppant sizes(which retain proppant pack porosity up to 15.2%) and higher proppant concentrations(which retain proppant pack porosity up to 29.5%) in the fracturing stimulations with higher in-situ stresses are recommended to de-escalate the critical consequences of crushing associated issues. Similarly, the selection of resin-coated proppants over ceramic and sand proppants may benefit in terms of obtaining reduced proppant embedment.In addition, selection of smaller proppant sizes and higher proppant concentrations are suggested for stimulation projects at depth with sedimentary formations and lower in-situ stresses where proppant embedment predominates. Furthermore, correlation between proppant embedment with repetitive loading cycles was studied.Importantly, microstructural analysis of the proppant-embedded siltstone rock samples revealed that the initiation of secondary induced fractures. Finally, the findings of this study can greatly contribute to accurately select optimum proppant properties(proppant type, size and concentration) depending on the oil/gas reservoir characteristics to minimize proppant crushing and embedment effects. | K.M.A.S.Bandara P.G.Ranjith T.D.Rathnaweera W.A.M.Wanniarachchi S.Q.Yang | 2021 | Geoscience Frontiers2021，12，6： | 2 |
| 3 | Evaluation on the anisotropic brittleness index of shale rock using geophysical logging显示文摘The brittleness index plays a significant role in the hydraulic fracturing design and wellbore stability analysis of shale reservoirs.Various brittleness indices have been proposed to characterize the brittleness of shale rocks,but almost all of them ignored the anisotropy of the brittleness index.Therefore,uniaxial compression testing integrated with geophysical logging was used to provide insights into the anisotropy of the brittleness index for Longmaxi shale,the presented method was utilized to assess brittleness index of Longmaxi shale formation for the interval of 3155e3175 m in CW-1 well.The results indicated that the brittleness index of Longmaxi shale showed a distinct anisotropy,and it achieved the minimum value at β=45°-60°.As the bedding angle increased,the observed brittleness index(BI2_β)decreased firstly and increased then,it achieved the lowest value at β=40°-60°,and it is consistent with the uniaxial compression testing results.Compared to the isotropic brittleness index(β=0°),the deviation of the anisotropic brittleness index ranged from 10%to 66.7%,in other words,the anisotropy of brittleness index cannot be ignored for Longmaxi shale.Organic matter content is one of the main intrinsic causes of shale anisotropy,and the anisotropy degree of the brittleness index generally increases with the increase in organic matter content.The present work is valuable for the assessment of anisotropic brittleness for hydraulic fracturing design and wellbore stability analysis. | Junchuan Gui Jianchun Guo Yu Sang Yaxi Chen Tianshou Ma P.G.Ranjith | 2023 | Petroleum2023，9，4： | 0 |
| 4 | Direct Evidence of Coal Swelling and Shrinkage with Injecting CO_(2) and N_(2) Using in-situ Synchrotron X-ray Microtomography显示文摘Deep coal seams are one of the world’s most widespread deposits for carbon dioxide(C02)disposal and are generally located near large point sources of CO_(2)emissions.The injection of CO_(2)into coal seams has great potential to sequester CO_(2)while simultaneously enhancing coalbed methane(CO_(2)-ECBM)recovery.Pilot tests of CO_(2)-ECBM have been conducted in coal seams worldwide with favorable early results.However,one of the main technical barriers in coal seams needs to be resolved:Injecting CO_(2)reduces coal permeability and well injectivity.Here,using in situ synchrotron X-ray microtomography,we provide the first observational evidence that injecting nitrogen(N_(2))can reverse much of this lost permeability by reopening fractures that have closed due to coal swelling induced by CO_(2)adsorption.Our findings support the notion that injecting minimally treated flue gas-a mixture of mainly N_(2) and CO_(2)-is an attractive alternative for ECBM recovery instead of pure CO_(2)injection in deep coal seams.Firstly,flue gas produced by power plants could be directly injected after particulate removal,thus avoiding high CO_(2)-separation costs.Secondly,the presence of N_(2)makes it possible to maintain a sufficiently high level of coal permeability.These results suggest that flue-gas ECBM for deep coal seams may provide a promising path toward net-zero emissions from coal mines. | Guanglei Zhang P.G.Ranjith Herbert E.Huppert | 2022 | Engineering2022，，11： | 0 |
| 5 | Three-dimensional failure behavior and cracking mechanism of rectangular solid sandstone containing a single fissure under triaxial compression显示文摘In actual rock engineering,fissures play an important role in determining the mechanical parameters of rock mass,whereas it is very difficult to construct fissures in cylindrical specimens.Therefore,the pre-fissured rectangular rock specimens were constructed innovatively.Moreover,a series of triaxial compression experimental results on the failure mechanical behavior of rectangular solid sandstone specimens containing a single fissure were reported.The lateral strain in different directions was monitored and the experimental results show that elastic modulus and axial strain increase non-linearly with confining pressure,and the average Poisson’s ratio parallel to fissure(μ2)is larger than that vertical to fissure(μ3).The cohesion,Hoek-Brown parameters of peak strength show similar trends with that of crack damage threshold to the fissure angle(α),and the parameters of the peak strength are larger than those of crack damage threshold.However,the internal friction angles of the peak strength and crack damage threshold are almost equal.Based on the geometries and properties of cracks,ten typical crack types are identified.Cracks vertical to pre-existing fissures occur in specimens under uniaxial compression,whereas cracks parallel to pre-existing fissures occur under triaxial compression.Finally,X-ray micro-computed tomography(CT)observations are conducted to analyze the internal damage mechanism of sandstone specimens with respect to various fissure angles.Reconstructed 3-D CT images indicate obvious effects of confining pressure and fissure angle on the crack system of sandstone specimens.This research elucidates the fundamental nature of rock failure under triaxial compression. | Sheng-Qi Yang Wen-Ling Tian P.G.Ranjith Xiang-Ru Liu Miao Chen Wu Cai | 2022 | Rock Mechanics Bulletin2022，1，1： | 0 |
| 6 | Experimental investigations on effects of gas pressure on mechanical behaviors and failure characteristic of coals显示文摘The mechanical behavior of coal is the key factor affecting underground coal mining and coalbed methane extraction.In this study,triaxial compression and seepage tests were carried out on coal at different gas pressures.The mechanical properties and failure process of coal were studied,as well as the acoustic emission(AE)and strain energy.The influence of gas pressure on the mechanical parameters of this coal was analyzed.Based on the conventional energy calculation formula,the pore pressure was introduced through the effective stress formula,and each energy component of coal containing gas was refined innovatively.The contribution of gas pressure to the total energy input and dissipation during loading was quantitatively described.Finally,the influence of gas pressure on coal strength was theo-retically analyzed from the perspectives of MohreCoulomb criterion and fracture mechanics.The results show that the total absorbed energy comprises the absorbed energy in the axial pressure direction(positive)and in the confining pressure direction(negative),as well as that induced by the pore pressure(initially negative and then positive).The absorbed energy in the axial pressure direction accounts for the main proportion of the total energy absorbed by coal.The quiet period of AE in the initial stage shortens,and AE activity increases during the pre-peak stage under high gas pressure.The fractal characteristics of AE in three stages are studied using the correlation dimension.The AE process has different forms of self-similarity in various deformation stages. | Yi Xue P.G.Ranjith Feng Gao Zhizhen Zhang Songhe Wang | 2023 | Journal of Rock Mechanics and Geotechnical Engineering2023，15，2： | 0 |
| 7 | Performances of fissured red sandstone after thermal treatment with constant-amplitude and low-cycle impacts显示文摘In the engineering practices,it is increasingly common to encounter fractured rocks perturbed by temperatures and frequent dynamic loads.In this paper,the dynamic behaviors and fracture characteristics of red sandstone considering temperatures(25℃,200℃,400℃,600℃,and 800℃)and fissure angles(0°,30°,60°,and 90°)were evaluated under constant-amplitude and low-cycle(CALC)impacts actuated by a modified split Hopkinson pressure bar(SHPB)system.Subsequently,fracture morphology and second-order statistics within the grey-level co-occurrence matrix(GLCM)were examined using scanning electron microscopy(SEM).Meanwhile,the deep analysis and discussion of the mechanical response were conducted through the synchronous thermal analyzer(STA)test,numerical simulations,one-dimensional stress wave theory,and material structure.The multiple regression models between response variables and interactive effects of independent variables were established using the response surface method(RSM).The results demonstrate the fatigue strength and life diminish as temperatures rise and increase with increasing fissure angles,while the strain rate exhibits an inverse behavior.Furthermore,the peak stress intensification and strain rate softening observed during CALC impact exhibit greater prominence at increased fissure angles.The failure is dominated by tensile damage with concise evolution paths and intergranular cracks as well as the compressor-crushed zone which may affect the failure mode after 400℃.The second-order statistics of GLCM in SEM images exhibit a considerable dependence on the temperatures.Also,thermal damage dominated by thermal properties controls the material structure and wave impedance and eventually affects the incident wave intensity.The tensile wave reflected from the fissure surface is the inherent mechanism responsible for the angle effect exhibited by the fatigue strength and life.Ultimately,the peak stress intensification and strain rate softening during impact are determined by both the material structure and compaction governed by thermal damage and tensile wave. | Yongjun Chen Tubing Yin P.G.Ranjith Xibing Li Qiang Li Dengdeng Zhuang | 2024 | Journal of Rock Mechanics and Geotechnical Engineering2024，16，2： | 0 |
| 8 | Experimental study on the influence of hydrostatic stress on the Lode angle effect of porous rock显示文摘To investigate the deformation mechanisms of rock under hydrostatic stress, destructive experiments were conducted on sandstone under different levels of hydrostatic stress and stress Lode angles. The results reveal that the shape of the strength envelope on the π plane gradually changes from the shape of the Lade criterion to the shape of the Drucker-Prage criterion with an increase in hydrostatic stress.Normally, there exists a deviation between the strain and stress paths for porous rocks on the π plane,and the deviation decreases with an increase in stress Lode angle and hydrostatic stress. A rock failure hypothesis based on the rock porous structure was proposed to investigate the reasons for the abovementioned phenomena. It was found that the shear expansion in the minimum principal stress direction is the dominant factor affecting the Lode angle effect(LAE);the magnitude of the hydrostatic stress induces the variation of the porous structure and influences the shear expansion. Therefore, the hydrostatic stress state affects the LAE. The failure hypothesis proposed in this paper can clarify the hydrostatic stress effect, LAE, and the variation of the rock strength envelope shape. | Zhenlong Song Zhenguo Zhang P.G.Ranjith Wanchun Zhao Chao Liu | 2022 | International Journal of Mining Science and Technology2022，32，4： | 0 |
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