Narrow Results

The coupled flow deformation behavior in the porous media has drawn tremendous attention in various scientific and engineering fields. It is reported that the porous media will be compressed and relative permeability in porous media will be changed as the effective stress increases. However, previous studies provided contradictory evidence for the stress-dependent irreducible water saturation and stress-dependent relative permeability. Until now, appropriate stress-dependent relative permeability curve for two-phase flow through porous media remains unclear. The goal of this work was to theoretically and experimentally study the stress-dependent relative permeability. Laboratory sample flooding tests were conducted to measure two-phase relative permeability in porous media under changing effective stress, and a corresponding theoretical model of stress-dependent relative permeability was derived to interpret the experimental results. The predictions from the proposed analytical model exhibited similar variation trends as the experimental data, which verified the theoretical model. Though the results for the stress-dependent relative permeability from previous studies are different, or even opposite, our proposed model with different conditions can provide explanations to these different results. This work provides a comprehensive experimental and theoretical study of stress-dependent relative permeability in porous media, which is beneficial to accurate performance forecasts for the coupled flow deformation behavior in porous media.

Relative permeability (RP) plays a critical role in fluid flow and transport in fracture systems, with considerable advances in theoretical and computational methods over the last few decades. Nevertheless, there is no standard procedure for measuring RP in fractures, and the essential controls on RP in rough fractures are not yet definitive. In this study, we developed a theoretical model to investigate the RP in inclined rough fractures under stress dependence based on fractal theory. The topography of the rough fracture surfaces is well addressed by fractal theory and lubrication theory, and thin bending theory is used to characterize permeability evolution characteristics of fractures under stress conditions. The model accounts for multiple key factors, including the microstructure of the rough fractures (e.g. the fractal dimension, the area ratio, the length ratio, and the maximum and minimum base radii), rock lithology (e.g. elastic modulus and Poisson’s ratio), gravity and effective stress. The predicted results agree well with the available experimental data. It is inferred that the effect of gravity on RP decreases as pressure gradient increases. In general, the theoretical fractal model reveals the coupled flow-deformation mechanisms in fractures, and tends to improve the efficacy of reservoir development strategies. With this new analytical solution, it can help to reduce the uncertainty in flow through fractures and obtain data with high accuracy.

The effect of the coal seam water infusion to reduce dust is directly related to the development degree of the coal structure under the action of the effective stress. Therefore, this paper first summarizes several basic effective-stress models and proposes the effective-stress model considering the capillary force. Thereafter, the nuclear magnetic resonance (NMR) experiment system high-voltage seepage module is used to achieve the saturation coal sample T${}_{2c}$ and water infusion coal sample T₂ test under different mechanical environments. And the fractal dimension was calculated based on the results of porosity and pore size test. Finally, the parameters were sequentially substituted into effective-stress models. The calculation results were compared and analyzed. The results show that the saturation levels of the irreducible fluid of Sample DLT and Sample XLZ are 92.93% and 93.66%, respectively, indicating that these samples are dense porous media structures. Meanwhile, the porosity test shows the overall porosity with the water infusion pressure and confining pressure changes being consistent with the conventional law; the partial porosity caused a slight fluctuation due to different sensitivities of different pores to stress. The effective stresses of the capillary force and the calculated effective stress of the body are closest to the fractal effective stress, so the difference between the two values is negligible due to the small capillary force, which indicates that during the high-pressure water infusion, the capillary force in the meso-structure hardly affects the mechanical environment. Based on the theoretical research results, this paper can provide a theoretical reference for the determination of water infusion parameters under different on-site mechanical environment during the process of coal seam water infusion, which is conducive to the popularization and application of this technology, thus, providing the scientific basis for safe mining of the deep coal seam and ensuring the safe and efficient production of mines.

With the increasing demand for energy, heat and mass transfer through porous media has been widely studied. To achieve accuracy in studying the behavior of heat transfer, a good knowledge of the effective thermal conductivity (ETC) of porous materials is needed. Because pore structure dominates the ETC of porous materials and effective stress leads to a change in pore structure, effective stress is one of the key influencing factors affecting ETC. In this study, considering the structure of surface roughness and pore size, based on fractal theory, a novel analytical solution at the pore scale for ETC of porous materials under stress conditions is proposed. Furthermore, in this model, capillaries in porous materials saturated with multiple phases have sinusoidal periodically constricted boundaries. The derived ETC model is validated against available experimental data. Moreover, the influences of the effective stress, initial effective porosity, roughness structure characterization, and wetting phase saturation on the ETC are analyzed. Compared with previous models, the rough surfaces of porous materials and the coupling of heat conduction and mechanics are taken into consideration to make the model more reasonable. As a result, this ETC model can better reveal the mechanism of heat conduction in porous media under stress conditions.

This study employs swelling deformation test for estimating the fractal dimension of salt-modified bentonite soil by measuring the void ratio of montmorillonite ($e_m$) and the effective stress ($p_e$). For the compacted Tsukinuno bentonite, a typical Na-montmorillonite, the fractal dimension is tested by the swelling deformation test conducted in sodium chloride solutions with different concentrations. According to the results, the fractal dimension of the specimens is essentially constant irrespective of the concentration of inundating NaCl solution. The strong correlation of the results from the swelling deformation test with those from the nitrogen adsorption test indicates that the swelling deformation test is an effective laboratory method for testing the fractal dimension of compacted bentonite in salt solution.

Development of a diagnostic tool for predicting the behavior of cerebral aneurysms was the inspiration of many research groups in recent years. In the present study a fluid–solid-growth (FSG) model for the early development of a cerebral aneurysm was presented in a 3D model of the internal carotid artery (ICA). This model is the result of two parallel mechanisms: first, defining arterial wall as a living tissue with the ability of degradation, growth and remodeling and second, full coupling of the wall and the blood flow. Taking into account the shear dependent nature of elastin degradation and mural-cell-mediated destructive activities, here, the degradation process has been linked to high effective stress of the vascular wall. The evolving properties of the elastinous and collagenous constituents have been predicted during the early development of the aneurysm and the code is applicable to more complicated aneurismal growth models.

A bow thruster mounted in the bow of a vessel is generally used to improve its maneuverability in ports. When a bow thruster is used near a berth, a jet generated from the bow thruster can cause sediment transport, resulting in local scouring of the seabed in front of quay walls. Countermeasures against such scouring are essential to ensure the stability of the quay walls. In recent years, new protective units called filter units have been used to protect seawalls and river dikes. However, it remains to be determined whether filter units covering the seabed in front of quay walls are effective in preventing jet-induced local scouring. In this study, jet-induced local scouring in front of a quay wall and its countermeasure using filter units are investigated using a three-dimensional two-way coupled fluid-sediment interaction model. The predictive capability of the three-dimensional coupled model is verified against experimental data in terms of average jet flow velocity, pore-water pressure, and the final seabed profile. The results show that the filter units covering the seabed prevent negative effective stress fluctuations on the surface layer of the seabed, and demonstrate the effectiveness of the countermeasure using the filter units.