Salt contamination has become the most critical challenge faced by water-based drilling fluids (WDFs) under extreme salinity and high temperatures, which deteriorates rheology and fluid loss ...properties, causing drilling accidents such as leakage, formation collapse and borehole instability. Herein, we report a salt-responsive zwitterionic polymer (PAMN) and its novel application as a tackifier in brine drilling fluid exploiting the anti-polyelectrolyte effect, in which the zwitterionic polymer molecular chain has undergone a transformation from a collapsed small spherical shape to an extended chain shape corresponding to the increasing ionic strength of the electrolyte. Compared with the saturated brine drilling fluid, the apparent viscosity and plastic viscosity of the saturated brine drilling fluid dispersed with PAMN increased by 542.9% and 925% respectively owing to the charge interaction on the molecular chain of PAMN was shielded by sodium chloride electrolyte, which resulted in the increase of the radius of gyration (Rg) of the PAMN molecular chain. Additionally, the salt response mechanism of zwitterionic polymer PAMN had been revealed by molecular simulation technology, which simulated the radius of gyration, radial distribution function (RDF), mean square displacement (MSD) and energy of molecular chain in water and salt water, respectively. This work demonstrates that the approach can be extensively generalized to a large class of synthetic zwitterionic polymers and can promote the development of various salt-responsive intelligent drilling fluids.
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•PAMN exhibited salt response and anti-polyelectrolyte effect.•The salt response of PAMN was successfully revealed by molecular simulation.•PAMN exhibited outstanding viscosity-increasing especially in brine drilling fluids.•PAMN can significantly reduce the fluid loss of brine drilling fluid.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
This paper presents the power dissipation analysis on high-temperature superconducting (HTS) coated conductor tapes and coils under the action of various oscillating currents and fields. The loss ...calculation on HTS coil was carried out by the H-formulation model implemented in the finite-element method (FEM) software package COMSOL Multiphysics. There were four different oscillating (ac) signals in this paper: sine, triangle, sawtooth, and square. Two scenarios causing loss in HTS tapes and coils which have been analyzed: Scenario 1 ac transport current; Scenario 2 ac magnetic field. The simulation results were compared to the experiment results with the typical sinusoidal ac signal.
Wellbore instability and formation collapse are crucial issues in the process of well excavation in the oil industry under extreme high temperature conditions. A novel zwitterionic quaternary ...copolymer (PDANV) of 4-vinylpyridine (VP), N, N-dimethylacrylamide (DMAA), 2-acrylamido-2-methylpropane sulfonic acid, N-vinylcaprolactam (NVCL) was synthesized in aqueous solution by free radical copolymerization reaction. The structure of PDANV was characterized by Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (1 H NMR), and the results indicated that ideal product are obtained. Thermal stability of PDANV was revealed by thermogravimetric analysis (TGA) and result showed that thermal degradation of PDANV mainly happened over 301°C. Simultaneously, PDANV was prepared to further evaluate its effect on rheological and filtration properties of water-based drilling fluids (WBDFs). The results showed that the fluid loss (FL
API
) of PDANV/WBDFs was only 3.4 mL, 6.0 mL before and after hot rolling at 260°C for 16 h, respectively. Compared with the 19.2% and 57.9% reduction of traditional fluid-loss additives CMC and Driscal, the fluid-loss reduction rate of PDANV/WBDFs was 87.5% in ultra-high temperature environment. Additionally, PDANV performed satisfactorily with great properties in WBDFs even at high concentration of salts and calcium. Therefore, it can be used for applications where the PDANV is subjected to certain harsh environments, such as extreme salinity and ultra-high temperature conditions.
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BFBNIB, GIS, IJS, KISLJ, NUK, PNG, UL, UM, UPUK
This paper focuses on the comparison of electromagnetic performance of the superconducting permanent magnet (SCPM) generators with two different topologies. The torque capabilities of the two ...generators are first investigated. The peak torque is largely restricted by the material characteristics of the superconducting (SC) and the permanent magnet. The SCPM generators with iron-cored rotor and iron-cored stator topology (IRIST) is superior to the one with iron-cored rotor and air-cored stator topology in terms of torque capability. Furthermore, the flux density, line electromotive force, torque and its torque ripple, and the efficiency of the designed generators are evaluated by using numerical model. The simulation results confirm that IRIST has higher output torque and efficiency with the penalty of higher harmonics and torque ripples.
High temperature superconducting (HTS) tapes could be introduced into large scale electrical machines in order to improve the power density. However, the alternating current (AC) loss of HTS tapes ...will cause the reduction of efficiency. On the basis of analytical and numerical model calculations, this paper presents an optimal design of the HTS armature winding aiming at lower AC loss. The main contribution of this work is that the relationship between the installation parameters and the AC loss of such HTS armature windings has been figured out based on the analysis of the shape feature of the HTS tape and the external magnetic field. When the tape is placed along a particular direction where the perpendicular component of external magnetic field has the lowest amplitude, the AC loss is the smallest. The modified installation location and angle are found based on the proposed generator. These results are verified using finite element method (FEM).
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
This paper discusses the average stochastic finite-time synchronization (ASFTS) for master-slave fuzzy neural networks (FNNs) with noises, a impulsive controller is designed to optimize the ...efficiency of the controller and take the controller into consideration. Uncertainty occurrs randomly, which improved the robustness of the controller. By constructing a suitable Lyapunov function and two monotonic increasing functions, sufficient conditions to achieve ASFTS are obtained, and the controller gain matrix is designed. Finally, we demonstrate the validity of our results with a numerical example.
As a sustainable alternative energy source, natural gas hydrate exploitation is limited by the risk of wellbore instability. The hydrate is usually distributed in unconsolidated shallow sediment with ...high clay content. A modified polyvinyl alcohol was proposed as a novel drilling fluid additive that could increase wellbore stability through chemical cementation and hydration inhibition. Under the action of modified polyvinyl alcohol, the linear expansion rate of the in situ deep-sea soil core was reduced from 18% to 1.9%, which remained the original shape after immersion for 24 h. The adsorption behavior was studied by atomic force microscopy, contact angle measurement and molecular dynamics simulations. The adhesion force was increased from 143.07 to 391.13 kcal/mol on the illite surface compared to the quartz surface by introducing positive functional groups in the modification process. The hydration peak decreased from 4.39 to 3.68 on the illite surface by occupying the interaction site between the rock surface and water molecules. This study provides a new method to ensure the safety of drilling and exploitation of natural gas hydrate and the development of drilling fluid additives for hydrate bearing sediment.
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•The dual effect of hydration inhibition and chemical cementation is achieved by modified polyvinyl alcohol.•Deep-sea soil is firstly used instead of montmorillonite for evaluation to simulate formation condition.•The mechanism of additives was investigated by molecular dynamics simulation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Utilizing the self-attention mechanism, Vision transformer (ViT) can tap long-distance dependencies and get excellent performance in vision tasks. However, it is difficult for ViT to learn rich ...characteristics with limited processing resources or data. As a result, based on the ViT model, we use a lightweight module that combines the information intersection of window self-attention and the inductive bias of convolutional neural network (CNN) to build a backbone network Convolution Lite Transformer (CLT). Further, experimental results show that CLT achieves 79.21 percent accuracy on the ImageNet with fewer parameters, which is more accurate than the traditional CNN model and more suitable for lightweight deployment compared with the ViT model.
This paper presents a 7 MW direct-drive permanent magnet wind power generator with tapering stator teeth and distributed arrangement of superconducting armature windings. Power density of the ...proposed machine is improved and the AC loss is reduced. These results are also verified using commercial finite element analysis software.
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