Shale gas transport in nanopores with mobile water films and water bridge

Gas flow properties in nanopores are significantly determined by the flow patterns. Slug flow pattern is a potential water–gas two phase flow pattern, in which gas molecules flow in form of gas slugs and water molecules separate gas slugs. Considering water slippage, a portion of water molecules accumulates at the wall with lower mobility, while the remaining water molecules take the shape of a water bridge. Adopting foam apparent viscosity model to represent slug rheological behavior, how water bridge disturbs on gas flow capacity is estimated. The results are compared with the water–gas two phase flow model that assumes annular flow pattern as well as the single gas flow model without the consideration of water. The comparison illustrates that gas molecular movement is significantly hindered by flow space reduction and loss of gas slippage. The impact from water phase of slug flow pattern is more significant than that of annular flow pattern on gas flow capacity. It is discovered that larger nanopores improve gas flow capacity while maintaining bulk water layer thickness and increasing water bridge thickness tend to reduce gas transport ability. A better understanding of the structure and transport of water and gas molecules is conducive to figure out the specific gas–water flow behavior and predict shale gas production.

A micro-investigation on water bridge effects for unsaturated granular materials with constant water content by discrete element method

The most common state of surface soil is unsaturated.Changes in water content will substantially impact its strength,leading to geological and engineering catastrophes.This paper used LIGGGHTS software to simulate the water bridge effect of unsaturated granular materials with constant water content and verify the rationality of the simplification of the stress-force-fabric(SFF)relationship.The results showed that the capillary force was not isotropic,which was different from the previous study,thus it cannot be overlooked in the simplification of the SFF relationship.Moreover,the influence of water content on the macroscopic mechanical behavior of unsaturated granular materials was interpreted through the evolutions of coordination number,interparticle force,fabric and force anisotropy,and other microscopic parameters.Compared to the literature,we found that different water bridge models would not change the characteristics of the solid skeleton.

Energy stored in nanoscale water capillary bridges formed between chemically heterogeneous surfaces with circular patches

The formation of nanoscale water capillary bridges(WCBs) between chemically heterogeneous(patchy) surfaces plays an important role in different scientific and engineering applications, including nanolithography, colloidal aggregation, and bioinspired adhesion. However, the properties of WCB of nanoscale dimensions remain unclear. Using molecular dynamics simulations, we investigate the geometrical and thermodynamic properties of WCB confined between chemically heterogeneous surfaces composed of circular hydrophilic patches on a hydrophobic background. We find that macroscopic capillary theory provides a good description of the WCB geometry and forces induced by the WCB on the confining surfaces even in the case of surface patches with diameters of only 4 nm. Upon stretching, the WCB contact angle changes from hydrophobic-like values(θ > 90°) to hydrophilic-like values(θ < 90°) until it finally breaks down into two droplets at wall separations of ~9–10 nm. We also show that the studied nanoscale WCB can be used to store relevant amounts of energy EPand explore how the walls patch geometry can be improved in order to maximize EP. Our findings show that nanoscale WCB can, in principle, be exploited for the design of clean energy storage devices as well as actuators that respond to changes in relative humidity. The present results can also be of crucial importance for the understanding of water transport in nanoporous media and nanoscale engineering systems.

BRIDGE OVER TROUBLED WATER

Guideline sets foundation for China and ASEAN to resolve the South China Sea dispute China and ASEAN countries have reached an agreement on a guideline for implementing the Declaration on the Conduct of Parties in the South China Sea(DOC),which lays a solid foundation for their practical cooperati on and will be helpful for the settlement of disputes in the area,said Chinese officials and scholars.

Bridge Over Troubled Water

Iraqi President Jalal Talabani’s first state visit to China paves the way for a new era in bilateral