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Purpose: The objective of this study was to evaluate and compare the biomechanical differences between clear aligner and fixed appliance in the traction of labially impacted canines based on 3D finite element analysis.Methods: A series of patient-oriented finite element models were constructed, including a maxillary dentition with a right labially canine, maxilla, periodontal ligaments, traction attachments, and clear aligners. The two most common clinical scenarios were investigated: Scenario A: impacted canine (distal) and Scenario B: impacted canine (mesial). For each clinical scenario, three traction models with clear aligners and one fixed appliance model were established.Results: In all four models, the impacted canines exhibited similar initial displacement tendencies of mesially rotated in Scenario A and distally rotated in Scenario B, and with small differences in periodontal ligament stress magnitude. However, the sum of the periodontal ligament stresses of the anchorage teeth in the clear aligner mode was in the range of 56.28–76.21 kPa and in the fixed appliance mode was in the range of 6.61–7.22 kPa. The maximum value of initial displacement of the anchorage teeth in the clear aligner mode was in the range of 13.71–19.72 μm, while in the fixed appliance mode was 3.10–3.92 μm.Conclusion: For impacted canines, clear aligner mode and fixed appliance mode have little difference in biomechanical effect. However, the anchorage teeth in the clear aligner mode endure higher stress and show a more pronounced displacement tendency. In addition, the biomechanical effects of different clear aligner traction models are various but not obvious.

Based on exploration and development results and evaluation of marine shale gas in South China in the past ten years, in view of the features of “high maturity, strong tectonic reformation and high shear stress” of the shale in Zhaotong exploration zone in the Yunnan and Guizhou Plateau, as well as the key issues of long time diffusion and leakage of shallow shale gas, and the preservation conditions, the factors controlling shallow shale gas sweet spot and key zone selection evaluation technology of shale gas are investigated. From 2017 to 2018, the first significant exploration breakthrough was made in the Taiyang anticline at a buried depth of 700 to 2 000 m, discovering large-scale proved geological reserves of shallow shale gas. By examining the accumulation conditions and sweet spot control factors of the shallow shale gas in this area, it is found that the accumulation and productivity potential of shale gas in the mountainous area with complex structure outside basin are controlled by five factors: (1) The gas-rich area has weak tectonic reformation and good preservation conditions on the whole, taking on typical anticline trap occurrence mode. (2) The gas-rich area is in over-pressure state and high in shale gas content. (3) The gas-rich area has high quality shale and thus superior source rock condition. (4) The gas-rich area has high quality reservoirs dominated by class I. (5) The shale gas reservoir in the gas-rich area has high content of brittle minerals and small difference between maximum and minimum horizontal stresses which are conducive to hydraulic fracturing. The innovative practice and core technologies formed during the exploration and production capacity construction of shallow shale gas in the Zhaotong demonstration zone have great reference significance for shallow shale gas exploration and development in other areas. Key words: shallow shale gas, Silurian Longmaxi Formation, Ordovician Wufeng Formation, exploration breakthrough, Taiyang anticline area, Zhaotong area, anticline

In order to assess the greatest impact of electrified railway on the power quality of the points of common coupling, a power quality prediction and evaluation method considering the impact of electrified railway is proposed. This paper explains the prediction and evaluation method based on a typical case of an electrified railway system. First, according to the characteristics of the traction power supply system, the power system, and all the different working conditions of the traction load, various power quality indicators at the public connection point are simulated and calculated. Then, combined with the power quality background harmonic test results of the substations, the power quality prediction evaluation results that take into account the impact of electrified railway are obtained. Finally, according to the requirements of the national standard, the limits of various power quality indicators are listed, and the prediction and evaluation conclusions are given by comparing the evaluation results and the limits. It provides a basis for the subsequent electrified railway power quality management plan and reactive power compensation device configuration.

Huangingba shale gas field is located at south edge of Sichuan basin. It has more complex structures, in-situ stresses and natural fracture corridors than its adjacent areas. Tested wells show huge variations of testing results. To identity production controlling factors is essential for optimizing productive drilling and completion in order to boost well productivities further. This paper presents a case study of Huangjingba shale gas field.Firstly, production data was analyzed to identify which parameter can be the best indicator of the current well productivities across the field. Secondly, data mining was conducted to correlate this indicator with reservoir quality, completion quality, and drilling and hydraulic fracturing operation parameters. The focus is on those factors that can be managed through drilling and completion optimization. Finally, after the most influential parameters were identified, rigorous simulations using a representative fine model were performed to reproduce observations and investigate their interactions and sensitivities on production. The model was refined from a three-dimensional (3D) field model, which integrates geology, natural fractures, reservoir and geomechanics together. It was calibrated by history matching of pumping history of hydraulic fracturing, microseismic data, and production history.Total gas content normalized to pore pressure and porosity can be a single-best factor for sweet-spot identification. Data analysis reveals the best interval for lateral placement. Simulations reproduce this observation and investigate what means can be taken to reduce negative impacts if one stage was outside the best interval. Proppant volume has the strongest correlation with production indicator for this high-stress field although other parameters of hydraulic fracturing are also analyzed. Results of production logging support this correlation. In order to increase effectively placed proppant volume, parametric study of hydraulic fracturing through simulation were completed. Field experiences and measurements suggest that natural fracture corridors can result in early screen-out, constrained stimulation volume, and duplicated stages. Unconventional fracturing modeling was utilized to investigate the optimal design and operational parameters of hydraulic fracturing.Our study suggests some key observations agree with the industrial best practices gathered from North America high-pressure shale plays. Yet abundant natural fracture corridors with complex patterns and distributions, formed through multiple tectonics in geological history, may present a unique feature of our field. It is also fundamentally different because of high in-situ stresses with extreme variations of heterogeneities and anisotropies. They require special cares on optimizing hydraulic fracturing in order to develop local best practice. Recent wells with newly proposed completion methodology achieve improved productivities.