Phenomenon of methane driven caused by hydraulic fracturing in methane-bearing coal seams

The methane concentration of the return current will always be enhanced to a certain degree when hydraulic fracturing with bedding drilling is implemented to a gassy coal seam in an underground coal mine. The methane in coal seam is driven out by hydraulic fracturing. Thus, the phenomenon is named as methane driven effect of hydraulic fracturing. After deep-hole hydraulic fracturing at the tunneling face of the gassy coal seam, the coal methane content exhibits a ‘‘low-high-low" distribution along excavation direction in the following advancing process, verifying the existence of methane driven caused by hydraulic fracturing in methane-bearing coal seam. Hydraulic fracturing causes the change of pore-water and methane pressure in surrounding coal. The uneven distribution of the pore pressure forms a pore pressure gradient. The free methane migrates from the position of high pore(methane) pressure to the position of low pore(methane) pressure. The methane pressure gradient is the fundamental driving force for methane-driven coal seam hydraulic fracturing. The uneven hydraulic crack propagation and the effect of time(as some processes need time to complete and are not completed instantaneously) will result in uneven methane driven. Therefore, an even hydraulic fracturing technique should be used to avoid the negative effects of methane driven; on the other hand, by taking fully advantage of methane driven, two technologies are presented.

3D-printed controllable gradient pore superwetting structures for high temperature efficient oil-water separation

Superwetting surfaces have the potential to address oil pollution in water,through their ability to separate the two.However,it remains a great challenge to fabricate stable and efficient separation structures using conventional manufacturing techniques.Furthermore,the materials traditionally used for oil-water separation are not stable at high temperature.Therefore,there is a need to develop stable,customizable structures to improve the performance of oil-water separation devices.In recent years,3D printing technology has developed rapidly,and breakthroughs have been made in the fabrication of complicated ceramic structures using this technology.Here,a ceramic material with a gradient pore structure and superhydrophobic/superoleophilic properties was prepared using 3D printing for high-efficiency oil-water separation.The gradient pore structure developed here can support a flux of up to 25434 L/m^(2)h,which is nearly 40%higher than that an analogous structure with straight pores.At 200℃,the oil-water separation performance was maintained at 97.4%.Furthermore,samples of the material exhibited outstanding mechanical properties,and chemical stability in a variety of harsh environments.This study provides an efficient,simple,and reliable method for manufacturing oil-water separation materials using 3D printing,and may have broader implications for both fundamental research and industrial applications.