Factors affecting reorientation of hydraulically induced fracture during fracturing with oriented perforations in shale gas reservoirs

Hydraulic fracturing with oriented perforations is an effective technology for reservoir stimulation for gas development in shale reservoirs. However, fracture reorientation during fracturing operation can affect the fracture conductivity and hinder the effective production of shale gas. In the present work, a numerical simulation model for investigating fracture reorientation during fracturing with oriented perforations was established, and it was verified to be suitable for all investigations in this paper. Based on this, factors (such as injection rate and fluid viscosity) affecting both of initiation and reorientation of the hydraulically induced fractures were investigated. The investigation results show that the fluid viscosity has little effect on initiation pressure of hydraulically induced fracture during fracturing operation, and the initiation pressure is mainly affected by perforation azimuth, injection rate and the stress difference. Moreover, the investigation results also show that perforation azimuth and difference between two horizontal principle stresses are the two most important factors affecting fracture reorientation. Based on the investigation results, the optimization of fracturing design can be achieved by adjusting some controllable factors. However, the regret is that the research object herein is a single fracture, and the interaction between fractures during fracturing operation needs to be further explored

Phase-field simulation of dendrite growth in Li-metal batteries

This thesis is two-dimensional phase-field modelling of dendrite growth in Li-metal batteries. It investigates the effects of varied Li nuclei states and working environments on the Li-ion electrodeposition and the optimal parameters for dendrite inhibition. Surface roughness, ion concentration evolution and temperature have been taken into consideration. Some possible approaches are proposed for effective dendrite inhibition

A Thermomechanical Model for Time-Varying Deformations of Spigot Interference Connection under Shrink-Fitting Assembly

The interference fit connection structure is widely employed in various industries. Different from the conventional connection structure, the aero-engine rotor connection has a spigot-bolt structure. The quality of the shrink-fitting assembly process directly affects the final assembly performance of the rotor. The complexity of the connection structure and the time-varying thermal deformation bring great challenges in analyzing the formation patterns of connection performance. However, existing methods of interference connection analysis are mainly used in the wide range of interference connection structures, which makes them difficult to apply in low height interference connection for aero-engine rotors. This paper introduces a thermomechanical interference fit pressure model. First, a theoretical model for interference fit pressure considering temperature-variable loads is established to obtain the time-varying pressure during the assembly process. Second, a finite element model is established to explore the influence of interference and temperature loads on the spigot pressure and the mounting edge deformation. Finally, the experiments validate the accuracy of both the theoretical model and the finite element analysis. The results indicate that during the shrink-fitting assembly process, the interference fit pressure exhibits a nonlinear evolution trend, and the warping deformation of the mounting edge is a result of the combined influence of temperature and interference fit pressure. The law found in this paper has an application prospect in the process parameter setting of shrink-fitting assembly for special structures

Effect of Surfactants with Different Hydrophilic–Lipophilic Balance on the Cohesive Force between Cyclopentane Hydrate Particles

Effective control of the cohesive force between hydrate particles is the key to prevent their aggregation, which then causes pipeline blockage. The hydrophilic–lipophilic balance (HLB) value of surfactants was proposed as an important parameter for the evaluation and design of hydrate anti-agglomerants. A microscopic manipulation method was used to measure the cohesive forces between cyclopentane hydrate particles in the presence of Tween and Span series surfactants with different HLB values; moreover, the measured cohesive force was compared with the results of calculations based on the liquid bridge force model. Combined with the surface morphology and wettability of the hydrate particles, we analyzed the mechanism by which surfactants with different HLB values influence the cohesion between hydrate particles. The results show that for both Tween (hydrophilic, HLB > 10) and Span (hydrophobic, HLB < 10) surfactants, the cohesive force between cyclopentane hydrate particles decreased with decreasing HLB. The experimental results were in good agreement with the results of calculations based on the liquid bridge force model. The cohesive force between hydrate particles increased with increasing concentration of Tween surfactants, while in the case of the Span series, the cohesive force decreased with increasing surfactant concentration. In the formation process of cyclopentane hydrate particles, the aggregation of low-HLB surfactant molecules at the oil–water or gas–water interface increases the surface roughness and hydrophobicity of the hydrate particles and inhibits the formation of liquid bridges between particles, thus reducing the cohesion between particles. Therefore, the hydrate aggregation and the associated blockage risks can be reduced

Characterization of a novel metal-dependent D-psicose 3-epimerase from Clostridium scindens 35704.

The noncharacterized protein CLOSCI_02528 from Clostridium scindens ATCC 35704 was characterized as D-psicose 3-epimerase. The enzyme showed maximum activity at pH 7.5 and 60°C. The half-life of the enzyme at 50°C was 108 min, suggesting the enzyme was relatively thermostable. It was strictly metal-dependent and required Mn²⁺ as optimum cofactor for activity. In addition, Mn²⁺ improved the structural stability during both heat- and urea-induced unfolding. Using circular dichroism measurements, the apparent melting temperature (T m) and the urea midtransition concentration (C m) of metal-free enzyme were 64.4°C and 2.68 M. By comparison, the Mn²⁺-bound enzyme showed higher T m and C m with 67.3°C and 5.09 M. The Michaelis-Menten constant (K m), turnover number (k cat), and catalytic efficiency (k cat/K m) values for substrate D-psicose were estimated to be 28.3 mM, 1826.8 s⁻¹, and 64.5 mM⁻¹ s⁻¹, respectively. The enzyme could effectively produce D-psicose from D-fructose with the turnover ratio of 28%

Theoretical Evaluation of Highly Efficient Nitrate Reduction to Ammonia on InBi

Electrocatalytic reduction of nitrate to ammonia has become a popular approach for wastewater treatment and ammonia production. However, the development of highly efficient electrocatalysts remains a great challenge. Herein, we systematically studied the potential of InBi for nitrate reduction to ammonia (NRA) based on density functional theory (DFT) calculations. Our results reveal that InBi exhibits high activity for NRA via an O-end pathway, where the free energy evolution of all intermediates is downhill in the most favorable elementary steps. The activation of nitrate originates from the strong orbital hybridization between oxygen and indium atoms, leading to an enhanced charge transfer as well as NO3- adsorption. In particular, the competing hydrogen evolution reaction (HER) is effectively suppressed due to the weak adsorption of proton. Our study not only proves the great electrocatalytic potential of InBi as a novel catalyst for NRA but also points out a new way to design NRA electrocatalysts for practical applications.</p

Formation-Damage Mechanism and Gel-Breaker-Free Drill-In Fluid for Carbonate Reservoir

Abundant oil and gas reserves have been proved in carbonates, but formation damage affects their production. In this study, the characteristics and formation-damage mechanism of the carbonate reservoir formation of the MS Oilfield in the Middle East were analyzed&mdash;utilizing X-ray diffraction, a scanning electron microscope, slice identification, and mercury intrusion&mdash;and technical measures for preventing formation damage were proposed. An &lsquo;improved ideal filling for temporary plugging&rsquo; theory was introduced, to design the particle size distribution of acid-soluble temporary plugging agents; a water-based drill-in fluid, which did not require gel-breaker treatment, was formed, and the properties of the drill-in fluid were tested. The results showed that the overall porosity and permeability of the carbonate reservoir formation were low, and that there was a potential for water-blocking damage. There were micro-fractures with a width of 80&ndash;120 &mu;m in the formation, which provided channels for drill-in fluid invasion. The average content of dolomite is 90.25%, and precipitation may occur under alkaline conditions. The polymeric drill-in fluid had good rheological and filtration properties, and the removal rate of the filter cake reached 78.1% in the chelating acid completion fluid without using gel breakers. In the permeability plugging test, the drill-in fluid formed a tight plugging zone on the surface of the ceramic disc with a pore size up to 120 &mu;m, and mitigated the fluid loss. In core flow tests, the drill-in fluid also effectively plugged the formation core samples by forming a thin plugging layer, which could be removed by the chelating acid completion fluid, indicated by return permeability higher than 80%. The results indicated that the drill-in fluid could mitigate formation damage without the treatment of gel breakers, thus improving the operating efficiency and safety

Experimental study of yarn friction slip and fabric shear deformation in yarn pull-out test

When designing circuits, engineers need to know the voltages and intensities at every point in the circuit. In simple circuits the results can be calculated by hand by using complex numbers, but in complex circuits this is impossible. This is why, nowadays, recourse is had to computer simulation so that circuits can be designed before being built, since it eliminates the need to build prototypes of the circuits with the ensuing time and cost. Bond-graph technique is a visual methodology that adds more transparency to the processes and it has turned out to be remarkably useful as it is a simple, effective method that can be applied to any physical system where there is a power exchange.This work initially analyses the starting mechanism of a direct current machine using bond graph technique, compares it with a model developed in Simulink copy and then stabilises the running of the motor by using a type PI controller