Hailong Liu

Lost circulation is the partial or complete loss of drilling fluid into a formation. It is among the major non-productive time events in drilling operations. Most of the lost circulation events are fracture initiation and propagation problems, occurring when the fluid pressure in a wellbore is high enough to create fractures in a formation. Wellbore strengthening is a common method to prevent or remedy lost circulation problems. Although many successful field applications have been reported, the fundamental mechanisms of wellbore strengthening are still not fully understood. There is still a lack of functional models in the drilling industry that can sufficiently describe fracture behavior in lost circulation events and wellbore strengthening. A finite-element framework was first developed to simulate lost circulation while drilling. Fluid circulation in the well and fracture propagation in the formation were coupled to predict dynamic fluid loss and fracture geometry evolution in lost circulation events. There are two common wellbore strengthening treatments, namely, preventive treatments based on plastering wellbore wall with mudcake before fractures occur and remedial treatments based on bridging/plugging lost circulation fractures. Two analytical models were developed for the investigation of preventive and remedial wellbore strengthening. The models developed and analyses conducted in this paper present a useful step towards the understanding of the fundamentals of lost circulation and wellbore strengthening, and provide improved guidance for lost circulation prevention and remediation.

In the blast furnace process, material losses occur due to mechanical wear between charged iron ore pellets and are exhausted in the form of dust in the off-gases. A redesigned tribometer combined with a ventilation chamber was developed to identify the dust emission from the mechanical wear contact of pellets. In order to obtain a better understanding of the measurement results, a coupled drift flux with a unified Eulerian deposition model was adopted to investigate particle dispersion and deposition during tests. Two influential factors, namely the air condition (5-20 L/min) and particle size (1-20 μm) were examined. The predicted results were presented by introducing two parameters, namely the measurable fraction and the deposition fraction. For each air condition, the measurable fraction declines while the deposition fraction rises as particle size grows. The critical size of the particles that becomes airborne and captured at the outlet was identified to be around 20 μm. In addition, a high airflow rate supplied at the inlet was observed to be favorable for improving the measurable fraction. Nevertheless, the results show that nearly 50% of emitted particles (1-20 μm) that failed to be captured during tests. Thus it could be expected that these generated particles would be transported deeply in a blast furnace if they are not efficiently removed from the off-gas. As a consequence, they may influence the quality of the products. Furthermore, the validation of the simulation results against the experimental data was achieved by using the predicted measurable fraction.

Depositing amorphous silicon doped with different elements on flexible substrates offers a large potential for the roll-to-roll processes lowering the manufacturing cost of solar cells. Unique magnetron sputtering method was adopted to deposit B-doped amorphous silicon thin film on flexible PET substrate instead of solid substrate materials like glass, metal and silicon. Effects of different substrates were investigated, as well as the processing parameters including sputtering power and working pressure. The structure and performance of the samples were characterized with SEM, XRD, surface profile meter and UV-spectrophotometer. The comparison between PET and glass shows that the alternative of PET substrate significantly improved the deposition rate. Optimal results were obtained as pressure of 0.2 Pa and RF power of 120 W, which showed the lowest transmittance as well as a minimum optical band gap, both are of great significance to photovoltaic conversion. Theoretical justification and experimental data including the feasible magnetron sputtering way, PET flexible substrate and optimized process parameters to the mass production of cheap and high performance heterojunction thin film solar cells were achieved.

Because of rapid economic development and urbanization, water shortage has become a serious problem in the arid region of China. To investigate urban water resource security, the supply demand pressure of water resources and the urban expansion index were analyzed under different developing scenarios in this paper. Based on the economic data of Urumqi, a typical inland city in the arid area, under the present development scenario from 2011 to 2030, a system dynamics model was constructed to simulate the water resource security. The results show that there will be great influence of urban expansion on water resource security in Urumqi in the future. Water resources are projected to become increasingly scarce if the urban expansion is left unchanged in terms of population, economic growth and water-use efficiency. To find a sustainable method for water resource use, four scenarios of urban expansion were set up based on the sensitive variables. Based on comparison of water consumption under the different scenarios, the harmonize scheme for urban water resource security is the best choice for the development of Urumqi. If the impact of urban expansion on urban water resource security alleviates in the future, the main parameters would have to reach a new standard of water use. Reducing the sewage and increasing the reuse proportion of wastewater are also very important for relieving the stress of water shortage. This research can serve as a reference for water resource allocation and urban planning in arid areas.