Photoelectrochemical water splitting can convert solar energy into clean hydrogen energy for storage. It is desirable to explore non-precious electrocatalysts for practical applications of a photoelectrode in a large scale. Here, we developed a facile spin-coating and in-situ photoelectrochemical reduction method to prepare a dispersed Cu electrocatalyst on a Si photocathode, which improves the performance remarkably. We find that thiourea in the precursor solution for spin-coating plays an important role in obtaining dispersed Cu particles on the surface of a Si photoelectrode. With thiourea in the precursor, the Cu/Si photocathode shows higher performance than the one without thiourea. Moreover, the Cu/Si photocathode also indicates good stability after 16 h illumination.
With the increasing demand for petroleum resources, the efficient development of unconventional resources is of great significance, such as tight oil. Hydraulic fracturing is necessary for the production of tight oil. However, it aggravates the reservoir heterogeneity with fracture network. With better fluid conformance control in the fractures, heterogeneity in tight oil reservoir will be improved. The high production period can be extended. In this study, the fracture equivalent width of the fracture network model was calculated with conversion coefficient R as 0.52ⅹ10 6 , 4.04ⅹ10 6 and 4.54ⅹ10 6 for the two, four and six turning points fracture network models, respectively. A dispersed particle gel (DPG) was used to control fluid mobility in tight oil fracture network model. The median particle size of this fluid is 3.17 μm and viscosity is 2.85 mPa s. In this study, it shows a better conformance control effect at a flow rate of 0.5 mL/min, with matching coefficient between DPG diameter and fracture equivalent width is 0.6. It is found that when the matching coefficient is less than 0.6, DPG can form unstable multi-layer stacking, and stable double-layer bridge stacking in the fracture when matching coefficient is 0.6. It would be single layer retention when it is greater than 0.6. With matching coefficient of 0.6, the conformance control rate would be 72.6% at flow rate 0.5 mL/min. This study would contribute to recovery the tight oil reservoir through heterogeneity remedy with conformance control in fracture network.
Li Weitao,Wei Falin,Xiong Chunming,Ouyang Jian,Zhao Guang,Shao Liming,Dai Mingli
Aiming at deep profile control in water flooding reservoirs, a heterogeneous combination flooding system, composed of dispersed particle gel (DPG) and a zwitterionic surfactant (THSB), was developed. The mean particle diameter was adjusted and then the DPG morphology and diameter were characterized using a laser scanning, confocal microscope, and dynamic light scattering. The effects of DPG concentration, temperature, pH, and salinity on THSB interfacial tension (IFT) were investigated. A method for determining DPG concentration was proposed, and the dynamic retention and migration mechanisms of the particles were evaluated, using cores with different permeabilities. Finally, the oil displacement mechanism of the combination flooding system was explored through visual simulation experiments and scanning electron microscopy. The results showed that the particle diameter was 2.5 μm, that compared with a surfactant system, the IFT of the combination flooding system was relatively low, and that the temperature, pH, and NaCl content of solutions had little effect on THSB IFT. Since specific matching relationships between DPG particles and reservoir pore throats existed, the retention amount and injection pressure were improved with the increased core permeability. Visual simulation experiments revealed the oil recovery mechanism of the combination flooding system. This combination flooding system can be used in reservoirs under varied conditions, as the particle diameter can be adjusted on a case-by-case basis, and the THSB surfactant proved to be high-temperature resistant and high-salinity tolerant. The combination flooding system can be applied to deep profile control and oil displacement, in oil fields.
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