Nanocrystalline silicon thin films were successfully prepared via a magnesiothermic reduction process. The initial magnesium content was restricted by the thickness of the film deposited on a quartz glass substrate by magnetron sputtering. After the magnesiothermic reduction process, the Raman spectroscopy results revealed a strong correlation between the thickness of the nanocrystalline thin films and the initial magnesium content. The thickness of the nanocrystalline thin films first increased to a maximum and then decreased as the initial magnesium content was further increased. Based on the solid-state reaction between Mg and SiO 2 , the mechanism behind this phenomenon is explained. In addition, the Raman spectroscopy results showed that the average grain size was almost constant and the crystalline volume fraction was found to be proportional to the silicon content. The band gap of the nanocrystalline silicon thin film was estimated to be 2.94 eV.
Cr buffer layers of six different thicknesses (100, 200, 300, 400, 500 and 600 nm) were respectively deposited on silicon substrate so as to constitute a series of Cr implantation layer/Cr buffer layer/tetrahedral amorphous carbon (ta-C) films. Analysis by SEM suggests that the implantation of Cr layer favourably improves the interfacial transition between ta-C film and Si substrate. X-ray diffraction detection reveals that the difference in thickness of Cr buffer layer does not significantly influence the crystalline structure. Raman result shows that the ductility of Cr buffer layer favours to remit stress of the ta-C film. Increase in Cr buffer layer thickness results in the reduction of nanohardness value. However, its elastic modulus and adhesion exhibit an initial increase followed by a decreasing fluctuation. Result of the study shows the accomplishment of superior mechanical properties for the ta-C film with 200 nm thick Cr buffer layer.
There is a rich coal bed methane reserve in the southeast margin of ordos basin. Hydraulic fracturing stimulation is the primary completion method to coal bed methane wellbores for many years in this area. Recently, V-Shape wells, which are complex architecture wells composed of a vertical well and two horizontal wells, are in order to improve recovery of CBM. Two horizontal wells intersect with vertical well in same depth, and the included angle between two well tracks of the plan projection is about 44 degree. Multistage hydraulic fracturing technology was treated two horizontal wells to create fracture network and induce nature fractures. Then, the vertical well was used to drainage to decrease bottom pressure.
Based on the geologic parameters, a total of eight stages were placed on two horizontal sections. One had three fractures, the other had five fractures. According to wellbore condition, pump bridge plug technology was used to execute multistage fracturing treatments. During field operation, 7200 m3 active water was mixed with quartz sand (492m3) and pumped down two wells together. The averaged proppant concentration was 14%. Because of included angle, the number of sand changed with stage increasing to avoid interference among fractures within two wells. And in the final stage, the treatment deployed 100m3 sand, and proppant loading reached to about 41750 Kg/m of net coal. This created a new Chinese record of proppant loading in coal bed methane.
Consequently, the first V-Shap well group was successfully treated in china. This work can research the application of special technology well in CBM, evaluate the effect of multi stimulation treatments, and confirm the gas content. It also provides the reliable guidance for the reasonable development of CBM reserve in the future.
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