Suffusion refers to a special form of internal erosion characterized by the selective erosion of the finest particles of a soil under the action of an internal fluid flow. In this work, the microscopic mechanism of particle detachment in binary mixtures subjected to suffusion under different flow directions is analyzed. We use the coupled lattice Boltzmann method (LBM) and discrete element method (DEM) to simulate the suffusion process in a granular sample subjected to an anisotropic stress state. When the macro flow direction is aligned with the principal direction of compression, it is found that the fluid flow is more intense, which increases erosion.The stress anisotropy also influences the detachment direction that is not necessarily correlated with the macroscopic flow direction. The sample's anisotropic stress state is responsible for directional variations in microstructural properties during the suffusion under different flow directions. From a micro scale point of view, a contact sliding index P and a particle detachment index Δ are defined to demonstrate that fluid-induced sliding dominates for particles about to detach.

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The dynamic effect in capillary pressure during the displacement process in ultra-low permeability sandstone reservoirs.

The multiphase fluid flow in the tight rocks can be affected by the existence of the dynamic effect, boundary slip, and boundary layer. In this work, a fractal bundle of the capillary tube model is proposed to incorporate the above-mentioned factors into the two-phase fluid flow characterization in tight porous media. The model has been successfully validated by the experimental data from core-flooding tests, demonstrating its effectiveness to describe the production behavior in tight reservoirs. In addition, sensitivity analysis is conducted to quantify the effects of the dynamic effect, boundary slip, boundary layer, and injection pressure on the oil recovery of the tight formations. Results indicate that the dynamic effect and boundary layer should be taken into consideration when predicting the production behavior, while the boundary slip can be neglected. The predicted recovery can be as high as 23% higher than its actual value if neglecting the dynamic effect while the existence of the boundary layer can decrease the oil recovery by up to 7%.

Unlike embankments, earth dams, and other man-made structures, most landslide dams are formed by rapid accumulation of rock or debris rather than mechanical compaction; thus, they are loose and pose a great risk of seepage failure. Landslide materials usually have complex pore structures with randomly distributed pores of various sizes, making the flow and transport processes very complex. Aiming at these challenges, we have studied the influences of pore structure on the micro-and macroscale flow characteristics of landslide materials. First, landslide materials are simplified as spherical granular packings with wide grain size distributions. Then, we use finite difference method (FDM) and lattice Boltzmann method (LBM) to simulate the fluid flow through granular packings and calculate their permeability. We find that both the correlation between pore-scale velocity and throat diameters and the correlation between macroscopic permeability and average throat diameters follow a power-law scaling with an exponent close to 2, in agreement with the Hagen-Poiseuille equation for laminar flow in pipes, suggesting that the relationships in complex pore structures are conformed with the simple theory. Moreover, we propose a new method by combining pore networks and complex networks to characterize the pore structure. The network analysis illustrates that granular packings with different permeability display distinctive distributions of pore throat size and pore connectivity and their correlations. Compared with disassortative pore networks, assortative ones generally have higher permeability. Furthermore, pores with larger closeness centrality have higher flow efficiency that results in higher macroscopic permeability.

Objective: Fat loss theory under various oxygen conditions has been disputed, and relevant systematic review studies are limited. This study is a systematic review and meta-analysis to assess whether hypoxic exercise training (HET) leads to superior fat-reducing compared with normoxic exercise training (NET).Methods: We searched PubMed, Web of Science, CNKI, ProQuest, Google Scholar, Cochrane Library, and EBSCOhost from inception to June 2022 for articles comparing the effects of hypoxic and normoxic exercise on body composition indicators, glycometabolism, and lipometabolism indicators in obese and overweight adults. Only randomized controlled trials (RCTs) were included. The effect sizes were expressed as standardized mean difference (SMD) and 95% confidence intervals (CI). Between-study heterogeneity was examined using the I2 test and evaluated publication bias via Egger’s regression test. The risk of bias assessment was performed for each included trial using Cochrane Evaluation Tool second generation. The meta-analysis was performed by using R 4.1.3 and RevMan 5.3 analytic tools.Results: A total of 19 RCTs with 444 subjects were analyzed according to the inclusion and exclusion criteria. Among them, there were 14 English literature and five Chinese literature. No significant difference in body composition (SMD -0.10, 95% CI -0.20 to -0.01), glycometabolism and lipid metabolism (SMD -0.01, 95% CI -0.13 to -0.10) has been observed when comparing the HET and NET groups. We only found low heterogeneity among trials assessing glycometabolism and lipometabolism (I2 = 20%, p = 0.09), and no publication bias was detected.Conclusion: The effects of HET and NET on fat loss in overweight or obese people are the same. The application and promotion of HET for fat reduction need further exploration.

Fine grains play an important role in mechanical properties of granular materials as they control how plastic strain may develop, which has a noticeable impact on mechanical stability. In this work, we use numerical simulations based on a discrete element method (DEM) to analyze the stress contribution of fine grains to the total stress. Different from usual DEM simulations, the analysis is conducted directly at the mesoscopic scale by considering an idealized grain assembly. The results show how fine grains get progressively jammed and increasingly participate to stress transmission. Fine contribution to contact stress is shown to be non-isotropic. The principal anisotropy direction coincides with the principal direction of contraction and the anisotropy ratio (i.e. the ratio between the largest and the smallest eigenvalues of the fine stress) is shown to be limited (𝜎 𝑚𝑎𝑥 𝜎 𝑚𝑖𝑛 ⁄ ≃ 2). By performing strain controlled directional analyses, an analytical model is proposed to account for the stress contribution of fine grains along various loading paths. Its simple form will help to enrich advanced micro-mechanically-based constitutive formulations, and better account for the constitutive behavior of widely graded granular materials.

Low salinity water flooding is a low-cost enhanced oil recovery (EOR) technology. The mechanism of EOR in a sandstone reservoir is still controversial, and there are many influencing factors. In this study, the effects of salinity (2000, 4000, 8000, and 100,000 ppm), pH (5.5 acidic, 7.0 neutral, and 8.0 alkaline), cation type (Na+ and Ca2+), and clay content (A rock 6.04%, B rock 11.94%) on zeta potential and recovery related to clay swelling were studied. The results showed that the absolute value of zeta potential increased with the decrease of salinity, cation changes from divalent to monovalent, and an increase of the pH value or clay content. The results of the SEM test before and after displacement and the continuous increase of displacement pressure after low salinity water injection show that low salinity water will cause clay swelling and the absolute value of zeta potential increased. The extreme value of recovery appears in the rocks with a high clay content: In neutral and alkaline NaCl solutions, RI and PEOR of rock B first increase and then decrease with the decrease of salinity. When the salinity is 4000 ppm, RI and PEOR were 8.16 and 34.13% in the neutral state, and 8.50 and 25.00% in the alkaline state, respectively. RI and PEOR of other experimental groups increased with the decrease of salinity. The study showed that the displacement pressure increases with the decrease of salinity, which indicates that the proper expansion of clay can improve the recovery of a sandstone reservoir, while the excessive expansion of clay will damage the reservoir and reduce the recovery. Based on the experimental results, the factors and indexes involved in the experiment were analyzed by multiple variance analysis. The result showed that the salinity, cationic type, and pH value have a significant effect on the zeta potential. All factors in the experiment have a significant effect on RI , salinity, and cationic type, and the clay content have a significant effect on PEOR. The conclusion of this study could guide the design of low-salinity water flooding technology in oil fields.