Nanoconfined methane flow behavior through realistic organic shale matrix under displacement pressure: a molecular simulation investigation

Academic investigations digging into the methane flow mechanisms at the nanoscale, closely related to development of shale gas reservoirs, had attracted tremendous interest in the past decade. At the same time, a good understanding of the complex essence remains challenging, while the broad theoretical scope, as well as application value, possesses great attraction. In this work, with the help of molecular dynamics methods nested in LAMMPS software, a fundamental framework is established to mimic the nanoconfined fluid flow through realistic organic shale matrix. Denoting evident discrepancy with existed contributions, shale matrix in this work is composed of specific number of kerogen molecules, rather than simple carbon-based nanotube. Recently, promotion efforts have been implemented in the academic community with the use of kerogen molecules, however, gas flow simulations are still lacking, and the pore shape in the current papers is always hypothesized as slit pores. The pore-geometry assumption seriously conflicts with the general observation phenomenon according to the advanced laboratory experiments, such as SEM image, AFM technology, that the organic pores tend to have circular pore geometry. In order to fill the knowledge gap, the circular nanopore with desirable pore size surrounded by kerogen molecules is constructed at first. The organic nanopore with various thermal maturity can be obtained by altering the kerogen molecular type, expecting to achieve more physically and theoretically similar to the realistic shale matrix. After that, methane flow simulation is performed by utilization of non-equilibrium molecular dynamics, the methane density as well as velocity distribution under different displacement pressures are depicted. Furthermore, detailed discussion with respect to the simulation results is provided. Results show that (a) displacement pressure acts as a dominant role affecting methane flow velocity and, however, fails to affect methane density distribution, a behavior mainly controlled by molecular–wall interactions; (b) the velocity distribution feature appears to be in line with the parabolic law under high atmosphere pressure, which can be attributed to small Knudsen number; (c) the simulation time will be prolonged with larger displacement pressure imposed on nanoconfined methane. Accordingly, this work can provide profound basis for accurate evaluation of nanoconfined gas flow behavior through shale matrix.

A Molecular Dynamics Investigation on Methane Flow and Water Droplets Sliding in Organic Shale Pores with Nano-structured Roughness

Roughness of surfaces significantly influences how methane and water flow in shale nanopores. We perform molecular dynamics simulations to investigate the influence of surface roughness on pore-scale transport of pure methane as well as of two-phase methane–water systems with the water sliding as droplets over the pore surface. For single-phase methane flow, surface roughness shows a limited influence on bulk methane density, while it significantly reduces the methane flow capacity. In methane–water systems, the mobility of water is a strong function of surface roughness including a clear transition between immobile and mobile water droplets. For cases with mobile water, droplet sliding speeds were correlated with pressure gradient and surface roughness. Sliding water droplets hardly deform, i.e., there is little difference between their advancing and receding contact angle with structured roughness.

Ensuring Explosion Safety of the Mine Methane Flow Meter during Operation, as well as at Primary and Periodic Calibration

At the mines where hazardous and threatening with sudden outburst emissions coal seams are developed, it is required to conduct a current forecast of the coal seams outburst hazard, which is based on an estimate of methane consumption from the control drill holes. Previously, the gas flow rate was measured using PG2-MA and IG-1 pressure gauges. Pressure gauges have some significant drawbacks. Their capillaries are regularly clogged with coal dust coming out from the control drill hole, which results in distortion of the measurement results. Pressure gauges do not register measured flow rate values, they do not have compensation for temperature errors. Metrological support is developed for pressure gauges that reduces the forecast accuracy and reliability. For eliminating above shortcomings, the development of modern mine methane flow meters was conducted based on the hot-wire measurement principle with electronic processing of the measured information. Cross-sectional area of the flow meter primary sensor is dozens of times larger compared to the pressure gauges, therefore the coal dust does not clog the gas path. The temperature error is automatically corrected. High-speed response ensures recording the real dynamics of gas release from the control drill hole. Several additional service functions are implemented. For electronic flow meters, the metrological support is developed and certified in accordance with the established procedure, including a method for checking the device with clean air (instead of methane) and an exemplary installation. Due to special circuitry solutions, the explosion-proof design of the CoalAwakeningBeast device with the type of protection «intrinsically safe electrical circuit» is provided, which is confirmed by the results of testing the flowmeter in the laboratories of MakNII and VostNII. Industrial tests conducted at the mines in four coal-mining basins confirmed the functionality of the device. In the Karaganda Technical University based on the development of Scientific and technical producer's cooperative NTPK Microclim (Karaganda, Kazakhstan), preparations are being made for a small-scale production of CoalAwakeningBeast flow meters.

The Effect of Increased Methane Flow Rate on Electronic Correlation of Amorphous Silicon Carbon (a-SiC: H)

In this study, we report for the first time that the addition of methane (CH4) flow rate in the p-type a-SiC: H layer greatly affects the electronic correlation in increasing the conversion efficiency of solar cells. The a-SiC: H p-type layer was grown using Plasma Enhanced Chemical Vapor Deposition (PECVD) on Indium Tin Oxide (ITO) substrate with various methane flow rates. The a-SiC: H p-type layer was characterized including the complex dielectric properties and the complex refractive index using Ellipsometric Spectroscopy (ES), while the surface roughness morphology was used Atomic Force Microscopy (AFM). In sample P-2 there is a change in the form of a decrease in the value of the refractive index < n > and the E0 energy in the lower energy compared to the P-1 sample with a change of 0.3 eV, an increase in the optical gap and a decrease in the value of the real and imaginary dielectric function. While the influence of an increase in the carbon composition of the amorphous network order shows the addition of amorphous tissue disorder. Our results, show that the optical magnitude of the p-type a-SiC: H layer is not only affected by the amount of carbon in the film but also the hydrogen which is thought to contribute.

Performance analysis of solid oxide fuel cell and micro gas turbine top-level cycle

First, a simulation model of the SOFC-MGT top-level combined cycle was established through Matlab/Simulink, and then the effect of different methane flow rates on the performance of the stack and the SOFC-MGT system was analyzed. The research results show that with the increase of methane flow, the power of the stack and SOFC-MGT system gradually increases, but the efficiency of the SOFC-MGT system gradually decreases with the increase of methane flow.