Detachment of authigenic reservoir fines by breakage with consequent migration in rock, straining, and permeability decline has been widely reported for several technological and natural processes. This phenomenon particularly calls for strong attention due to decline in well production and injection rates. This paper presents laboratory corefloods performed in a wide range of flow rates with monitoring of breakthrough fines concentrations and pressure drops across the overall core and its first section. The corefloods are accompanied by X-ray diffraction (XRD) analysis and optical microscopy imaging. The data are tuned with a mathematical model for fines migration, resulting in the quantification of particle detachment across the range of studied velocities. The variation of particle detachment over velocity shows two distinct regions of detachment supporting the hypothesis of two mechanisms of fines detachment by: (i) breakage due to particle deformation and induced stresses and (ii) viscous drag that exceeds the attaching electrostatic forces. This allows determining the attached concentrations separately for authigenic and detrital fines. The results have important implications for understanding the susceptibility of natural rocks to formation damage by fines migration as well as in designing prevention and remediation strategies.
Microwave-assisted rock breaking has attracted increasing attention because of its potential to weaken hard rock and facilitate mechanical excavation. However, damage accumulation and fracture evolution in hard rock subjected to repeated microwave heating and water quenching remain insufficiently understood. In this study, granite specimens were subjected to cyclic microwave heating–quenching (MHQ). Ultrasonic testing, uniaxial compression tests, acoustic emission (AE) monitoring, and scanning electron microscopy (SEM) were combined to investigate the deterioration of physical and mechanical properties and the evolution of fracture behavior. The results showed that cyclic MHQ treatment promoted crack development and reduced structural integrity, as reflected in increasingly distorted ultrasonic waveforms, a shift in dominant frequency toward lower frequencies, and progressive decreases in P-wave velocity and mechanical properties. After nine cycles, the P-wave velocity, uniaxial compressive strength, and elastic modulus decreased by 58.49
Preconditioning rock masses with high–low temperature cycles can enhance the rock-breaking efficiency of Tunnel Boring Machines (TBM) in extremely hard rocks. To determine an optimal temperature scheme, granite samples were subjected to varying heating temperatures and cycle counts, followed by strength and punch penetration tests. The effects of thermally induced cracks on failure modes and boreability were analyzed, and an Energy-Adjusted Boreability Index (EABI) was proposed to evaluate performance considering both boreability and energy consumption. Results show that intergranular cracks develop with increasing temperature, while intragranular cracks appear in feldspar above 500 °C and in quartz above 600 °C. At 800 °C, feldspar spalling forms surface micro-pits. Thermal cycling has limited influence on crack density but promotes crack widening. With increasing temperature, the uniaxial compressive strength decreases, exhibiting a transition from slow to accelerated degradation at approximately 300 °C. In contrast, the Brazilian tensile strength shows a shift from rapid to gradual reduction, with a transition at about 600 °C. The influence of cyclic heating on UCS degradation becomes particularly pronounced at 600 °C. And 600 °C is the onset of the brittle-to-plastic transition. A single thermal cycle at 600 °C achieves the minimum EABI and reduces the MLI by 32.9
The average fragment size is a key indicator for characterizing rock fragmentation and is strongly influenced by both the strain rate and sample size. Existing studies have focused primarily on the influence of the strain rate on the average fragment size. Research on the coupling effect of the strain rate and sample size has been largely experimental, whereas theoretical investigations into this coupling remain limited. Therefore, the coupling effect of the strain rate and sample size on the average fragment size of rock is investigated theoretically in this work. On the basis of the Weibull activation law for rock defects and the shortest time criterion for crack coalescence at different scale levels, the YTGC model is revised to incorporate sample size effects, thereby establishing a coupling model that simultaneously accounts for the influences of the strain rate and sample size on the average fragment size. The effects of the strain rate and sample size on the average fragment size are analyzed. The underlying mechanisms governing the effects of the strain rate and sample size on the average fragment size are revealed. The results show that the average fragment size decreases with increasing strain rate in a negative power law, i.e., dε̇^ - 2 / . -0pt 3 , which is consistent with existing theoretical models. Moreover, increasing the sample size also results in a decrease in the average fragment size, indicating a pronounced negative correlation. At low Weibull modulus, the strain rate effect is dominant, whereas with increasing Weibull modulus, the sample size effect becomes progressively more significant. A comparison between the model predictions and available experimental data shows good agreement, thereby validating the rationality of the proposed model. The proposed model provides a theoretical basis for the design and optimization of fragmentation parameters in engineering applications such as rock blasting.
