A coupled fluid-flow and geomechanics model for simulating coalbed methane (CBM) recovery is presented. In the model, the fluid-flow process is simulated with a triple-porosity/dual-permeability ...model, and the coupling effects of effective stress and micro-pore swelling/shrinkage are modeled with the coupled fluid-flow and geomechanical deformation approach. The mathematical model is implemented with a finite volume method. First, a case without considering coupling between fluid-flow and geomechanics is simulated and compared with an existing simulator. The effects of coupled fluid-flow and geomechanics are then studied in detail with two illustrative examples. The first one is designed for testing the effective stress effect without micro-pore swelling/shrinkage effect, and the other for testing the coupling effects of the effective stress and micro-pore swelling/shrinkage on the methane production. The numerical results indicate that both the effective stress and the micro-pore shrinkage make a significant contribution to fluid-flow in CBM reservoir and to methane production. The methane production sensitivity to Young’s modulus and Langmuir sorption strain are investigated as well. Finally, we make a dynamic analysis of the coupling effects of fluid-flow process and geomechanics.
The detection of oil-dissolved gases (such as CO, CH4 and H2) in transformers on-line is an important technology to predict and judge the operating status of transformers. Microstructure and gas ...sensing performance of Au-MoS2 microspheres synthesized by hydrothermal method were investigated in the present research. The results indicated Au-MoS2 based gas sensor has excellent response to CO, CH4 and H2 gases with maximum responses of 25.48, 16.75 and 8.48 at 30 ppm in their optimum working temperature (150 °C, 150 °C, 175 °C). In addition, First-principle calculation was carried out to expound the sensing mechanism in detail. The conclusions of this study suggest that Au-MoS2 monolayer exhibits a promising applicable future in sensor detecting of oil-dissolved gases in power transformer.
The hierarchical flower-like Au-MoS2 microspheres were favoring synthesized using simple hydrothermal method and their microstructure are measured. Gas sensing performance and atomic level gas sensing mechanism of MoS2 microspheres to CO, CH4 and H2 was investigated. We found Au-MoS2 microspheres gas sensor has good gas sensing performances and Au-MoS2 monolayer exhibits excellent adsorption capacity to three target gases. Display omitted
•The hierarchical flower-like Au-MoS2 microspheres were synthesized via simple hydrothermal method.•Au-MoS2 microspheres gas sensor shows good gas sensing properties to CO, H2 and CH4.•The excellent adsorption performances of Au-MoS2 monolayer to CO, H2 and CH4 were discussed in detail.•Theoretical studies have been applied to analyze the gas sensing mechanism of Au-MoS2 microspheres to CO, H2 and CH4.
•Extended previous method from 2D to 3D and show its applicability in non-Gaussian fields.•Proposed another algorithm using power average and determine coefficient analytically.•Used new formulas for ...off-diagonal terms in conductivity tensor with positive-definiteness.
We propose an efficient analytical upscaling method to compute the equivalent conductivity tensor for elliptic equations in three-dimensional space. Our approach uses perturbation expansion and Fourier analysis, and considers heterogeneity, anisotropy and geometry of coarse gridblocks. Through low-order approximation, the derived analytical solution accurately approximates the central-difference numerical solution with periodic boundary conditions. Numerical tests are performed to demonstrate the capability and efficiency of this analytical approach in upscaling fluid flow in heterogeneous formations. We test the method in synthetic examples and benchmark cases with both Gaussian random fields and channelized non-Gaussian fields. In addition, we examine the impact of each parameter on the upscaled conductivity, and investigate the sensitivity of the variance and correlation lengths to the coefficients. We also indicate how to extend this approach to multiphase flow problems.
Oil-immersed power transformers are considered to be one of the most crucial and expensive devices used in power systems. Hence, high-performance gas sensors have been extensively explored and are ...widely used for detecting fault characteristic gases dissolved in transformer oil which can be used to evaluate the working state of transformers and thus ensure the reliable operation of power grids. Hitherto, as a typical n-type metal-oxide semiconductor, tungsten trioxide (WO
3
) has received considerable attention due to its unique structure. Also, the requirements for high quality gas detectors were given. Based on this, considerable efforts have been made to design and fabricate more prominent WO
3
based sensors with higher responses and more outstanding properties. Lots of research has focused on the synthesis of WO
3
nanomaterials with different effective and controllable strategies. Meanwhile, the various morphologies of currently synthesized nanostructures from 0-D to 3-D are discussed, along with their respective beneficial characteristics. Additionally, this paper focused on the gas sensing properties and mechanisms of the WO
3
based sensors, especially for the detection of fault characteristic gases. In all, the detailed analysis has contributed some beneficial guidance to the exploration on the surface morphology and special hierarchical structure of WO
3
for highly sensitive detection of fault characteristic gases in oil-immersed transformers.
A new photocatalyst, Er2FeSbO7, was prepared by solid phase sintering using the high-temperature synthesis method for the first time in this paper. Er2FeSbO7/BiTiSbO6 heterojunction (EBH) catalyst ...was prepared by the solvent thermal method for the first time. Er2FeSbO7 compound crystallized in the pyrochlore-type architecture and cubelike crystal system; the interspace group of Er2FeSbO7 was Fd3m and the crystal cellular parameter a of Er2FeSbO7 was 10.179902 Å. The band gap (BDG) width of Er2FeSbO7 was 1.88 eV. After visible light irradiation of 150 minutes (VLGI-150min) with EBH as a photocatalyst, the removal rate (RR) of enrofloxacin (ENR) concentration was 99.16%, and the total organic carbon (TOC) concentration RR was 94.96%. The power mechanics invariable k toward ENR consistency and visible light irradiation (VLGI) time with EBH as a photocatalyzer attained 0.02296 min−1. The power mechanics invariable k which was involved with TOC attained 0.01535 min−1. The experimental results showed that the photocatalytic degradation (PCD) of ENR within pharmaceutical waste water with EBH as a photocatalyzer under VLGI was in keeping with the single-order reactivity power mechanics. The RR of ENR with EBH as a photocatalyzer was 1.151 times, 1.269 times or 2.524 times that with Er2FeSbO7 as a photocatalyst, BiTiSbO6 as a photocatalyst, or N-doping TiO2 (N-TO) as a photocatalyst after VLGI-150min. The photocatalytic activity, which ranged from high to low among above four photocatalysts, was as follows: EBHP > Er2FeSbO7 > BiTiSbO6 > N-TO. After VLGI-150min toward three periods of the project with EBH as a photocatalyst, the RR of ENR attained 98.00%, 96.76% and 95.60%. The results showed that the stability of EBH was very high. With appending trapping agent, it could be proved that the oxidative capability for degrading ENR, which ranged from strong to weak among three oxidic radicals, was as follows: superoxide anion > hydroxyl radicals (HRS) > holes. This work provides a scientific basis for the research and oriented leader development of efficient heterojunction catalysts.
As a new heavy oil development technology, hot water chemistry flooding has great potential in offshore heavy oil fields development. In this paper, the adaptability of hot water chemical flooding ...was studied based on the typical model of offshore heavy oil fields. The main controlling factors affecting the hot water chemical flooding were analyzed and evaluated by single factor analysis. The technical boundary was established for offshore heavy oil fields. In addition, the hot water chemical flooding scheme was designed by a case study of a well group oilfield D. The results indicate that crude oil viscosity and well spacing have great influences on hot water chemical flooding performance. Hot water chemical flooding is favorable when the crude oil viscosity is between 300 and 1000 mPa·s and well spacing is around 200~400 m. The hot water chemical flooding scheme of the target well group results in 40.2×104 tons of incremental oil, and 6.3% of recovery factor being enhanced, which shows strong evidence that hot water chemical flooding enables great oilfield development performance.
Originally, the new catalyst Bi2SmSbO7 was synthesized by the hydrothermal synthesis method or by the solid-phase sintering method at a lofty temperature. A solvothermal method was utilized to ...prepare a Bi2SmSbO7/ZnBiYO4 heterojunction photocatalyst (BZHP). The crystal structure of Bi2SmSbO7 belonged to the pyrochlore structure and face-centered cubic crystal system by the space group of Fd3m. The cell parameter a was equivalent to 10.835(1) Å (Bi2SmSbO7). With Bi2SmSbO7/ZnBiYO4 heterojunction (BZH) as the photocatalyst, the removal rate (RR) of direct orange (DO) and the total organic carbon were 99.10% and 96.21% after visible light irradiation of 160 min (VLI-160M). The kinetic constant k toward DO concentration and visible light irradiation time (VLI) with BZH as photocatalyst reached 2.167 min−1. The kinetic constant k, which was concerned with total organic carbon, reached 0.047 min−1. The kinetic curve that came from DO degradation with BZH as a catalyst under VLI conformed to the second-order reaction kinetics. After VLI-160M, the photocatalytic degradation (PD) removal percentage of DO with BZH as the photocatalyst was 1.200 times, 1.268 times or 3.019 times that with Bi2SmSbO7 as the photocatalyst, ZnBiYO4 as the photocatalyst or with nitrogen-doped titanium dioxide as the photocatalyst. The photocatalytic activity (PA) was as following: BZH > Bi2SmSbO7 > ZnBiYO4 > nitrogen-doped titanium dioxide. After VLI-160M for three cycles of experiments with BZH as the photocatalyst, the RR of DO reached 98.03%, 96.73% and 95.43%, respectively, which meant that BZHP possessed high stability. By using the experiment of adding a trapping agent, the oxidative purifying capability for degradation of direct orange, which was in gradual depressed order, was as following: hydroxyl radical > superoxide anion > holes. Finally, the possible degradation pathway and degradation mechanism of DO were discussed systematically. A new high active heterojunction catalyst BZHP, which could efficiently remove toxic organic pollutants such as DO from dye wastewater after VLI, was obtained. Our research was meant to improve the photocatalytic property of the single photocatalyst.
Hydrogen sulfide (H
2
S) is an important decomposition component of sulfur hexafluoride (SF
6
), which has been extensively used in gas-insulated switchgear (GIS) power equipment as insulating and ...arc-quenching medium. In this work, electrospun ZnO-SnO
2
composite nanofibers as a promising sensing material for SF
6
decomposition component H
2
S were proposed and prepared. The crystal structure and morphology of the electrospun ZnO-SnO
2
samples were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. The composition of the sensitive materials was analyzed by energy dispersive X-ray spectrometers (EDS) and X-ray photoelectron spectroscopy (XPS). Side heated sensors were fabricated with the electrospun ZnO-SnO
2
nanofibers and the gas sensing behaviors to H
2
S gas were systematically investigated. The proposed ZnO–SnO
2
composite nanofibers sensor showed lower optimal operating temperature, enhanced sensing response, quick response/recovery time and good long-term stability against H
2
S. The measured optimal operating temperature of the ZnO–SnO
2
nanofibers sensor to 50 ppm H
2
S gas was about 250°C with a response of 66.23, which was 6 times larger than pure SnO
2
nanofibers sensor. The detection limit of the fabricated ZnO–SnO
2
nanofibers sensor toward H
2
S gas can be as low as 0.5 ppm. Finally, a plausible sensing mechanism for the proposed ZnO–SnO
2
composite nanofibers sensor to H
2
S was also discussed.
Injection conformance reversion commonly observed during polymer flooding in offshore heterogeneous heavy-oil reservoirs weakens the volumetric sweep of polymer solution and compromises its EOR ...results. To investigate its mechanisms and impact factors, one mathematical model to predicate injection conformance behavior is constructed for heterogeneous reservoirs based on the Buckley-Leverett function. The different suction capability of each layer to polymer solution results in distinct change law of the flow resistance force, which in turn reacts upon the suction capability and creates dynamic redistribution of injection between layers. Conformance reversion takes place when the variation ratio of flow resistance force of different layers tends to be the same. The peak value and scope of conformance reversion decrease and reversion timing is advanced as oil viscosity or permeability contrast increases, or polymer concentration or relative thickness of low permeable layer decreases, which compromises the ability of polymer flooding to improve the volumetric sweep and lower suction of the low permeable layer. The features of offshore polymer flooding tend to make the injection conformance V-type and create low-efficiency circulation of polymer in a high permeable layer more easily. These results can provide guidance to improve the production performance of polymer flooding in offshore heterogeneous heavy-oil reservoirs.
Introduction:
The hot water chemical flooding technology effectively improves the fluidity ratio and enhances the horizontal and vertical oil displacement efficiency of the reservoir through the ...synergistic effect of thermal energy and chemicals, which can further enhance the recovery rate on the basis of throughput thermal recovery.
Methods:
Based on the geological reservoir parameters of Bohai B oilfield, an oil recovery system evaluation experiment and scheme design study were carried out. Injection parameters such as hot water temperature, chemical agent concentration, and chemical agent dosage that affect the oil recovery effect of hot water chemical flooding were optimized and designed. The development characteristics and effects of two thermal recovery technologies, namely multi thermal fluid throughput and hot water chemical flooding, were compared and analyzed.
Results:
The results show that with the increase of temperature, the effect of chemical agents on improving the water-oil mobility ratio and reducing the viscosity of crude oil is weakened, and the thermal energy plays a leading role in enhancing oil recovery, but when the temperature is higher than 115°C, the improvement of oil recovery is slowed down, and the comprehensive economic indicators decline rapidly. As the concentration of chemical agent increases, the enhanced oil recovery increases monotonously. When the concentration is 1500 mg/L, the comprehensive economic indicators reach the peak and then decline, indicating that the efficiency of chemical agent decreases. The total amount of chemical agent shall be controlled within 0.25 ~ 0.30 PV. The case calculation shows that hot water chemical flooding can expand the effective radius from 80 m to 400 m, more effectively use the reserves between injection and production wells, increase the oil recovery by 4.8 percentage points, and increase the oil yield by 31.7 m
3
/t per ton of agent.
Discussion:
It is suggested that Bohai B Oilfield can adopt hot water chemical flooding after the multiple thermal fluid huff and puff to continuously guarantee the oilfield production.
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