The thermal conductivity of a molecular gas consists of the translational and internal parts. Although in continuum flows the total thermal conductivity itself is adequate to describe the heat ...transfer, in rarefied gas flows they need to be modelled separately, according to the relaxation rates of translational and internal heat fluxes in an homogeneous system. This paper is dedicated to quantifying how these relaxation rates affect rarefied gas dynamics. The kinetic model of Wu et al. (J. Fluid Mech., vol. 763, 2015, pp. 24–50) is adapted to recover the relaxation of heat fluxes, which is validated by the direct simulation Monte Carlo method. Then the model of Wu et al., which has the freedom to adjust the relaxation rates, is used to investigate the rate effects of thermal relaxation in problems such as the normal shock wave, creep flow driven by Maxwell's demon and thermal transpiration. It is found that the relaxation rates of heat flux affect rarefied gas flows significantly, even when the total thermal conductivity is fixed.
As natural gas demand surges in China, driven by the coal-to-gas switching policy, widespread attention is focused on its impacts on global gas supply-demand rebalance and greenhouse gas (GHG) ...emissions. Here, for the first time, we estimate well-to-city-gate GHG emissions of gas supplies for China, based on analyses of field-specific characteristics of 104 fields in 15 countries. Results show GHG intensities of supplies from 104 fields vary from 6.2 to 43.3 g CO
eq MJ
. Due to the increase of GHG-intensive gas supplies from Russia, Central Asia, and domestic shale gas fields, the supply-energy-weighted average GHG intensity is projected to increase from 21.7 in 2016 to 23.3 CO
eq MJ
in 2030, and total well-to-city-gate emissions of gas supplies are estimated to grow by ~3 times. While securing gas supply is a top priority for the Chinese government, decreasing GHG intensity should be considered in meeting its commitment to emission reductions.
•New AGP models for the organic and inorganic nanopores were developed.•Effects of pore radius, pressure, and surface diffusion coefficient on gas transport behaviors are analyzed.•Numerical model ...for a fractured well in shale based on the AGP model and DFM model was developed.•Influences of different parameters on gas transport behaviors of the fractured well were discussed.
The combined action of multiple transport mechanisms and reservoir characteristics makes gas transport behaviors in nanoporous shale complicated. Accurate apparent gas permeability (AGP) characterization for gas transport in nanopores is crucially essential for macroscale modeling in shale gas reservoirs development. In this study, a new unified AGP model for gas transport in the organic and inorganic nanoporous shale (OM and IM) is presented, incorporating multiple mechanisms, such as real gas effect, viscous-slip flow, Knudsen diffusion, surface diffusion, stress dependence and especially the organic nanopores content. Besides, the effect of multilayer adsorption on gas transport is included. The model is validated by experimental and linearized Boltzmann results and compared with the published AGP models. After that, sensitivity analysis and the contribution of each mechanism to the total AGP are conducted. Moreover, a numerical model for the fractured well in shale based on the presented AGP model and discrete fracture model (DFM) is derived. The finite element method (FEM) is applied to solve the model and then influence factors of gas transport behaviors are discussed. The results show that different transport mechanisms exist in organic and inorganic nanopores respectively. The larger pore radius or pressure causes a smaller ratio of the AGP over the intrinsic permeability. Moreover, the contribution of surface diffusion to the total AGP is significantly influenced by the OM nanopores radius and surface diffusion coefficient. In addition, gas transport is governed by Knudsen diffusion in nanopores with a small radius and low pressure and is controlled by viscous flow under the large pore radius and high-pressure conditions. Then, the presented AGP model is introduced into the macroscale numerical model for a fractured well in shale. Larger hydraulic fracture half-length, OM nanopores content and matrix pore radius as well as smaller natural fracture spacing cause higher gas production. The study provides a new unified AGP model considering gas transport behaviors in nanopores and applies the AGP model to macroscale modeling.
Anyue gas field is a large gas field located in the central Sichuan Basin, China. Although many studies have been carried out previously, the formation mechanism of this field is unclear and ...currently under debate. To better understand the accumulation history, the role that groundwater plays in transporting hydrocarbons within sedimentary basins and water-gas interactions, stable and noble gas isotopes were measured in thirteen free gas samples from the Anyue gas field. In addition, nine formation water samples and five reservoir bitumen samples were analyzed for stable carbon isotopes. δ13C(CH4) values in the gas samples range from −35.0 to −32.6‰, showing evidence of thermogenic origin. δ13C values among three different types of samples (free gases, water-dissolved gases and reservoir bitumen) show a pattern that cannot be explained by oil cracking followed by free gas accumulation. It suggests the occurrence of gas-groundwater interaction in the Anyue field. Free gas samples can be divided into 2 distinct groups by their geographical locations and stratigraphical source formations. 3He/4He ratios (R/Ra) in group 1 and group 2 samples range from 0.0118 to 0.0132 and 0.0115 to 0.0256, respectively, indicating He is mainly derived from the crust. 20Ne/22Ne and 21Ne/22Ne ratios suggest a mixing between the air and crust sources. 40Ar/36Ar ratios ranging from 1658 to 2109 and 2168 to 5973 in group 1 and group 2 samples, respectively, are significantly higher than the air value of 298.6. In comparison, heavier noble gas (Kr and Xe) isotopic compositions are predominantly air-like. The relative enrichment of 4He and 21Ne* in group 1 samples can be possibly explained by preferential release of light noble gases in a low temperature environment. Samples in group 2 show a good fit to the solubility-controlled Rayleigh fractionation model, suggesting the presence of an open system degassing of gases from the groundwater. The excess heavy noble gases in natural gas samples can be attributed to the addition of sedimentary components from the source rocks during geological evolution. 4He groundwater ages considering in-situ production and external flux indicate the addition of young groundwater into the Anyue gas field. Low gas-groundwater ratios and high CH4/36Ar ratios suggest that only a small portion of the gases in the current Longwangmiao reservoir of Anyue gas field has been in contact with the relatively young groundwater. Based on the noble gas and stable carbon isotope results in all samples, we propose a two-stage gas and groundwater interaction process during the gas preservation and accumulation history in the Anyue gas field in China.
This paper discusses the direct fabrication of ultrathin Ni(OH)2 nanosheets on substrates via a facile solvothermal process, which is free from the use of additional surfactants. The precursor is ...converted into porous NiO nanosheets via heat treatment. The thickness and morphology of the nanosheets is controlled by manipulating the ethanol content in the solvent. The acetone sensing performance of all samples has been evaluated, as observed, the 75% ethanol-based NiO gas sensor (NiO-75), demonstrates ultrahigh acetone sensitivity, the response value can reach 60%, when the NiO nanosheet sensor detects 100 ppb acetone gas, ultralow detection limit (0.8 ppb acetone), and good stability. The excellent sensing performance of the NiO nanosheets can be attributed to their porous structure, which provides a large surface area and crystal facet with affinity to acetone gas. Moreover, the porous structure facilitates the diffusion of gas samples and products to improve the acetone detection sensitivity. Furthermore, the NiO-75 sensor demonstrates superior acetone selectivity, against other interfering gases. The findings of this study indicate that low cost NiO nanosheets fabricated via a simple process could be considered as potential, candidates for use in commercial acetone sensing applications.,
•Ultrathin and Porous NiO nanosheets are synthesized through a facile one-step solvothermal method on gas sensor substrate.•The 75% ethanol-based gas sensor can detect acetone gas with a concentration as low as 10 ppb at optimum temperature.•The high acetone sensing performance of NiO nanosheets is owing to the large surface area induced by the porous structure.
Abstract
Currently, the Russian Federation is one of the largest natural gas producers in the world, second only to the United States in production. The world’s largest proven gas reserves are ...located in Russia. Despite the colossal initial volumes of gas, many unique Russian fields have been operating in a declining production mode for a long time (for many years) and are steadily approaching the transition to the mode of fields with low-pressure gas, which is currently economically unprofitable to compress for supply to main gas pipelines for transportation to consumers. New gas and oil and gas condensate fields of the Russian Federation are located in new undeveloped regions of Russia. These areas are distinguished by a harsh climate, lack of transport infrastructure, are located far from existing gas pipelines and are characterized, as a rule, by a complex geological structure and multicomponent gas composition, which inevitably entails a further increase in the already considerable capital and operating costs, time lag, which, accordingly, reduces economic attractiveness of their development for gas producers. In this regard, additional exploration and production of gas from the Achimov deposit - formations lying below the developed Valanginian deposits of large gas fields, close to the transition to closure, is of great interest. The production of gas from the Achimov deposit at fields with a built infrastructure, where there is a connection to the main gas pipelines, can significantly reduce costs - both production and capital. The article is devoted to the issues of modelling gas production of the Achimov deposit.
In the nineteenth century, horse transportation consumed vast amounts of land for hay production, and the intense traffic and ankle-deep manure created miserable living conditions in urban centers. ...The introduction of the horseless carriage solved many of these problems but has created others. Today another revolution in transportation seems overdue. Transportation consumes two-thirds of the world's petroleum and has become the largest contributor to global environmental change. Most of this increase in scale can be attributed to the strong desire for personal mobility that comes with economic growth. In Transportation in a Climate-Constrained World, the authors present the first integrated assessment of the factors affecting greenhouse gas (GHG) emissions from passenger transportation. They examine such topics as past and future travel demand; the influence of personal and business choices on passenger travel's climate impact; technologies and alternative fuels that may become available to mitigate GHG emissions from passenger transport; and policies that would promote a more sustainable transportation system. And most important, taking into account all of these options are taken together, they consider how to achieve a sustainable transportation system in the next thirty to fifty years.
At local scales, emissions of methane and carbon dioxide are highly uncertain. Localized sources of both trace gases can create strong local gradients in its columnar abundance, which can be ...discerned using absorption spectroscopy at high spatial resolution. In a previous study, more than 250 methane plumes were observed in the San Juan Basin near Four Corners during April 2015 using the next-generation Airborne Visible/Infrared Imaging Spectrometer (AVIRIS-NG) and a linearized matched filter. For the first time, we apply the iterative maximum a posteriori differential optical absorption spectroscopy (IMAP-DOAS) method to AVIRIS-NG data and generate gas concentration maps for methane, carbon dioxide, and water vapor plumes. This demonstrates a comprehensive greenhouse gas monitoring capability that targets methane and carbon dioxide, the two dominant anthropogenic climate-forcing agents. Water vapor results indicate the ability of these retrievals to distinguish between methane and water vapor despite spectral interference in the shortwave infrared. We focus on selected cases from anthropogenic and natural sources, including emissions from mine ventilation shafts, a gas processing plant, tank, pipeline leak, and natural seep. In addition, carbon dioxide emissions were mapped from the flue-gas stacks of two coal-fired power plants and a water vapor plume was observed from the combined sources of cooling towers and cooling ponds. Observed plumes were consistent with known and suspected emission sources verified by the true color AVIRIS-NG scenes and higher-resolution Google Earth imagery. Real-time detection and geolocation of methane plumes by AVIRIS-NG provided unambiguous identification of individual emission source locations and communication to a ground team for rapid follow-up. This permitted verification of a number of methane emission sources using a thermal camera, including a tank and buried natural gas pipeline.
Microbial methanogenesis is a key biogeochemical process in the carbon cycle that is responsible for 70% of global emissions of the potent greenhouse gas methane (CH4). Further knowledge about ...microbial methanogenesis is crucial to mitigate emissions, increase climate model accuracy, or advance methanogenic biogas production. The current understanding of the substrate use of methanogenic microbes is limited, especially regarding the methylotrophic pathway. Here, we present fiber-enhanced Raman spectroscopy (FERS) of headspace gases as an alternate tool to study methanogenesis and substrate use in particular. The optical technique is nondestructive and sensitive to CH4, hydrogen (H2), and carbon dioxide with a large dynamic range from trace levels (demonstrated LoDs: CH4, 3 ppm; H2, 49 ppm) to pure gases. In addition, the portable FERS system can provide quantitative information about methanol concentration in the liquid phase of microbial cultures through headspace gas sampling (LoD 25 ppm). We demonstrate how FERS gas sensing could enable us to track substrate and product levels of microbial methanogenesis with just one instrument. The versatility of Raman gas spectroscopy could moreover help us to elucidate links between nitrogen and carbon cycle in microbial communities in the near future.
Highlights • Intestinal gas species can be used as biomarkers for specific gut microbiota. • These gases affect the status of the gut and subsequently human health. • Advances in sensors and ...electronic technologies have led to the development of gas capsules and in vitro fermentation systems. • These novel systems can be used as reliable and cost-effective human health assessment units.
PDF
