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The tubing used in a gas well rarely collapses and fails during applying annulus pressure. In this study, the failure causes of tubing collapse were analyzed by means of data verification, macroscopic observation, magnetic particle inspection, physical and chemical inspection, optical microscopy, and tubing collapse test. Mechanical analysis of the string and full-scale physical simulation test simulating downhole working conditions. Finally, the verification analysis of the collapse test is carried out by the finite element analysis (FEA). The results showed that (1) the physical dimension, physical and chemical properties, and collapse resistance of this batch of tubing met the requirements of the tubing ordering technical standard. (2) Assuming that the well packer slip was unsealed and could slide freely, the mechanical theoretical analysis of collapsed tubing string and collapse test under simulated working condition load was carried out, which reproduced the load when the tubing collapsed. It can be seen from this that the packer did fail. (3) The FEA calculation results showed that when the external pressure was greater than 30.75 MPa, it would inevitably lead to collapse failure in case of packer unsealed. In conclusion, the root cause for the collapse failure of the 105th underground tubing string was that the packer lost its sealing function, resulting in an abnormal axial load. While under the action of external pressure, the tubing was overloaded and collapsed. It is recommended to carry out verification tests on the material performance of packer slip, the dimensional changes of packer tool outer diameter and inner diameter under actual well conditions, the creep behavior of packer seal, and the performance of shear pin under actual working conditions, especially in the well containing H2S, so as to prevent the pressure leakage of gas well annulus caused by packer unsealing and the reoccurrence of such downhole string collapse accidents. The first collapse test under simulated working condition load is conducted in this paper. Analyzing the collapse failure work and putting forward suggestions to effectively prevent similar failures from happening again are of great significance to the oilfield. [ABSTRACT FROM AUTHOR]

A novel low-molecular-weight organogelator (1) based on thiacrown-cyclized tetrathiafulvalene has been synthesized through cross-coupling reaction of crown-fused 1,3-dithiole-2-one 3 and the thione 4 in the presence of triethyl phosphite. The molecular structure of 1 was fully characterized by nuclear magnetic resonance spectroscopy, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, and infrared spectroscopy. Gel-forming-ability experiments showed that the gelator could only form an opaque gel in dimethyl sulfoxide by sonication. The xerogel morphology observed by scanning electron microscopy showed an amorphous wrinkled structure. The gel exhibited varied responses to various external stimuli, including temperature, chemical oxidation, anions, and Na+ ions. [ABSTRACT FROM AUTHOR]

A key challenge in the design of magnetic molecules with intramolecular charge transfer behavior is to obtain reversible magnetic bistability triggered by external stimuli. Here, we show that two dinuclear metal complexes, [(bbp)Fe(CN)3Mn(Py5Me2)]·2.5CH3OH (4) and [(bbp)Fe(CN)3Ni(Py5Me2)]·2.5CH3OH (5) (Py5Me2 = 2,6-bis(1,1-di(pyridine-2-yl)ethyl)pyridine, H2bbp = 2,6-bis(benzimidazole-2-yl)pyridine), were self-assembly synthesized by (Bu4N)2[(bbp)FeIII(CN)3] and [Mn(Py5Me2)(OH2)](ClO4)2 or [Ni(Py5Me2)(OH2)](ClO4)2, respectively. Complexes 4 and 5 exhibited intramolecular metal-to-metal charge transfer with the addition of acids or bases in solution by UV–visible spectrophotometric measurements and electrochemistry studies, and concomitant switching of the {FeIII(μ-CN)MnII/NiII} state to the {FeII(μ-CN)MnIII/NiIII} state. [ABSTRACT FROM AUTHOR]

Wide-angle X-ray scattering (WAXS) based upon synchrotron radiation is ideal for the in situ study of crystal structural changes during heating at high temperatures. This contribution describes a small furnace for in situ WAXS. The furnace has a wide coverage of scattered/diffracted angle from 0 to 135°, heats samples from room temperature to 1000 °C at 20 °C/min, and is suitable for in situ WAXS and radial distribution function of materials. Temperature calibration and safety verification are provided. The use of the furnace is demonstrated by in situ WAXS for the carbonization of bituminous coal. [ABSTRACT FROM AUTHOR]

Aiming at establishing the transient flow characteristics of gas–liquid two-phase flow in high-undulation water pipelines, based on the bubble distribution law measured using physical tests, the bubble distribution law function was input into the hump-pipe fluid domain model, and CFD numerical simulation was carried out for different flow rates and different air contents. The CLSVOF two-phase flow model and the RNG k-ε turbulence model were used to analyze the flow pattern evolution and pressure pulsation propagation in the process of gas–liquid two-phase flow through a hump pipe. The results show that the bubble size has a lognormal distribution, the equivalent diameter is between 3 mm and 10 mm, and the evolution of the flow pattern in the hump pipe is complex and violent. In the horizontal pipe section, there are three main flow patterns: bubble flow, wavy flow and segment plug flow. In the vertical pipe, there are two main flow patterns, slug flow and churning flow, and the flow pattern is affected by the flow rate and the air content rate. When air bubbles or air pockets in the pipeline flow through a certain area, this leads to a steep increase and decrease in the pressure pulsation amplitude in the region, and the pressure fluctuation is extremely frequent. Compared with the water flow rate, the air content is the main factor affecting the relative pressure pulsation amplitude under the condition of a 0.15-air content operating mode, which is generally approximately two to six times that of the 0-air content operating mode. The results of the research should facilitate the prediction of stagnant gas pipeline system bursts and water hammer protection, providing a theoretical basis and calculation parameters. [ABSTRACT FROM AUTHOR]

The shaped hierarchical porous carbon derived from ZIF-8, MSNs (mesoporous silica nanoparticles) and CS (chitosan) has been prepared by in situ assembly and post-annealing process. By tunning carbonization temperatures (from 450 to 650 °C), a series of CS/ZIF-8/MSNs carbonaceous millimetre-sized spheres with honeycomb internal structures and hierarchical pores have been developed for CO2 uptake. CS/ZIF-8/MSNs-525 (the sample treated at 525 °C) exhibited a higher CO2 capacity (1.32 mmol/g, 1 atm) than that of other samples due to its appropriate mesopores (∼11 nm), micropores (∼0.73 nm) and BET surface area (∼459.2 m2g−1). The XRD pattern of CS/ZIF-8/MSNs-525 suggested that MSNs would not affect sample structure, which performed largely maintained ZIF-8 diffraction. The SEM/EDS image of CS/ZIF-8/MSNs-525 showed that MSNs (∼50 nm) has been well decorated onto the surface of ZIF-8 by in situ assembly and carbonization, thus indicating a hierarchical structure formed. In addition, the TG-MS technology has been also utilized to clarify that MSNs assembly would not affect the carbonization process during the formation of CS/ZIF-8/MSNs-525. Moreover, the addition of MSNs facilitated a proper pore structure and higher CO2 capacity of CS/ZIF-8/MSNs-525 compared with that of CS/ZIF-8 carbon spheres (0.9 mmol/g, 1 atm). Particularly, the CS/ZIF-8/MSNs-525 exhibited excellent stability and recyclable performance after CO2 adsorption in 10 adsorption-desorption cycles. This MSNs assembly strategy could induce a simple way for obtaining novel shaped carbonaceous adsorbent for superior CO2 uptake in industrial fields. [ABSTRACT FROM AUTHOR]

With the increasing complexity of shale gas extraction conditions, a large number of high-strength collapse-resistant casing is applied to the extraction of unconventional oil and gas resources. There are errors in the traditional API collapse strength formula. A high-precision and low-computational-cost model is needed for predicting the strength of high-collapsible casing. The key influencing factors of casing anti-collapse strength were determined as outer diameter, wall thickness, yield strength, ovality, wall thickness unevenness, and residual stress by analyzing the casing collapse mechanism. In response to the key factors mentioned above, a dataset was formed by measuring the geometric parameters of the full-size casing and collecting data on the results of the anti-collapse strength experiment, which was divided into a training set (70%) and a testing set (30%). Three machine-learning algorithms, a neural network, random forest, and support vector machine, were trained to predict the anti-extrusion strength. The correlation coefficient R2, root mean square error RMSE, and average relative MRE were used to evaluate the indexes for model preference evaluation. The results show that machine-learning algorithms have unique advantages in casing anti-collapsing strength prediction. Within which, the neural network prediction model has the best prediction effect, and its characteristics of high precision, low cost and high efficiency are more suitable for the prediction of casing extrusion strength. Its testing set R2 is 0.9733, RMSE is 0.0267 and MRE is 0.0782, and the prediction accuracy can reach 92.2% which is much higher than the API calculation result (63.3%). The network prediction model is suitable for casing anti-collapsing strength prediction and meets the actual prediction requirements. [ABSTRACT FROM AUTHOR]

Understanding how applied voltage drives the electrocatalytic reaction at the nanoscale is a fundamental scientific problem, particularly in non-metallic electrocatalysts, due to their low intrinsic carrier concentration. Herein, using monolayer molybdenum disulfide (MoS2) as a model system of non-metallic catalyst, the potential drops across the basal plane of MoS2 (ΔVsem) and the electric double layer (ΔVedl) are decoupled quantitatively as a function of applied voltage through in-situ surface potential microscopy. We visualize the evolution of the band structure under liquid conditions and clarify the process of EF keeping moving deep into Ec, revealing the formation process of the electrolyte gating effect. Additionally, electron transfer (ET) imaging reveals that the basal plane exhibits high ET activity, consistent with the results of surface potential measurements. The potential-dependent behavior of kf and ns in the ET reaction are further decoupled based on the measurements of ΔVsem and ΔVedl. Comparing the ET and hydrogen evolution reaction imaging results suggests that the low electrocatalytic activity of the basal plane is mainly due to the absence of active sites, rather than its electron transfer ability. This study fills an experimental gap in exploring driving forces for electrocatalysis at the nanoscale and addresses the long-standing issue of the inability to decouple charge transfer from catalytic processes. [ABSTRACT FROM AUTHOR]

The identification of flood hazards during emerging public safety crises such as hurricanes or flash floods is an invaluable tool for first responders and managers yet remains out of reach in any comprehensive sense when using traditional remote-sensing methods, due to cloud cover and other data-sourcing restrictions. While many remote-sensing techniques exist for floodwater identification and extraction, few studies demonstrate an up-to-day understanding with better techniques in isolating the spectral properties of floodwaters from collected data, which vary for each event. This study introduces a novel method for delineating near-real-time inundation flood extent and depth mapping for storm events, using an inexpensive unmanned aerial vehicle (UAV)-based multispectral remote-sensing platform, which was designed to be applicable for urban environments, under a wide range of atmospheric conditions. The methodology is demonstrated using an actual flooding-event—Hurricane Zeta during the 2020 Atlantic hurricane season. Referred to as the UAV and Floodwater Inundation and Depth Mapper (FIDM), the methodology consists of three major components, including aerial data collection, processing, and flood inundation (water surface extent) and depth mapping. The model results for inundation and depth were compared to a validation dataset and ground-truthing data, respectively. The results suggest that UAV-FIDM is able to predict inundation with a total error (sum of omission and commission errors) of 15.8% and produce flooding depth estimates that are accurate enough to be actionable to determine road closures for a real event. [ABSTRACT FROM AUTHOR]

Frequent changes in the tide levels in estuaries cause constant changes in the hydraulics of fish passage systems, with important effects on successful fish passage and swimming behavior. In most cases, Japanese eels often have low passage rates in engineered fishways because of their special habits. In this study, we established a 1:4 scaled-down weir-hole combination bulkhead fishway, studied the effects of different tidal differences and water depths on the passage rates and swimming behavior of yellow-phase Japanese eels, and analyzed the response of the Japanese eels to the hydraulic factors by superimposing their swimming trajectories and the flow field simulation results. We found that the passage rate of the eels decreased from 68.18% to 50.00% and 45.45% under extreme high tide differences and extreme low tide differences, respectively. The eels tended to use the low-velocity area to climb up the wall, and when crossing the mainstream, the yellow-phase Japanese eels preferred the area with a flow velocity of 0.1~0.36 m/s and a turbulent kinetic energy range of 0.001~0.007 m2/s2. Their upstream swimming speed was maintained at a range of 0.1~0.3 m/s. [ABSTRACT FROM AUTHOR]