页岩气开采与深地微生物的相互影响

页岩气是一种特殊的天然气聚集,以吸附或游离状态存在于页岩之中。页岩气资源储量丰富,约占全球天然气能源的三分之一,主要分布在中国、北美、俄罗斯等国家和地区。页岩气开采所使用的水力压裂技术会对深地微生物产生显著影响,在水力压裂的不同阶段,微生物群落组成存在明显差异。其中,产甲烷菌能够提高页岩气的产量,而产酸细菌会造成设备腐蚀,降低页岩气的回收效率。本文概述了页岩气的开采现状、开采过程以及微生物种群的变化和潜在影响,以期促进页岩气开采与深地微生物相互影响的研究,最终推动页岩气的绿色、高效开采。     

Kinetic measurements of gas exchange in the intact pulmonary microcirculation.

The kinetics of gas exchange are monitored in an isolated perfused lung preparation contained within a plethysmograph. The lungs are perfused with buffer, and there is no gas exchange until a 2.0-ml bolus of reactant is injected into the perfusion system. Subsequent gas exchange produces a pressure transient that is related to the corresponding volume of exchanged gas. The observed rate of volume change is the result of two separate processes: 1) the rate of gas exchange during transit through the capillary bed and 2) the distribution of vascular transit times between the point of injection and the capillary bed. The latter is assessed by a control injection containing a dissolved inert gas that is liberated in the alveoli as the bolus enters the capillary bed. Analysis of the experimental curves permits the separation of these two processes. A model of exchange kinetics indicates that this method has the capability of measuring kinetic events occurring during gas exchange in the microcirculation under physiological conditions.     

Measurement of respiratory gas exchange during artificial respiration

This paper reports a new system for the continuous measurements of respiratory gas exchange in ventilated subjects. It involves mixing some of the inspired gas with all of the expired gas and withdrawing the mixture at a constant rate through a dry gas meter that measures the flow. The inspired gas and expired gas mixtures are sampled and O2 and CO2 concentrations measured with a paramagnetic gas analyzer and a capnograph, respectively, to an accuracy of 0.01%. Evidence is presented to confirm the necessary stability and sensitivity of these instruments. It is possible to use the system with high inspired O2 concentrations, with ventilators where there is incomplete separation of inspired and expired gas, and in the presence of intermittent mandatory ventilation, positive end-expiratory pressure, and continuous airway pressure. The system was compared with the N2-dilution method and with the collection of expired gas in a Douglas bag in dog experiments and with patients in the intensive therapy unit. Excellent correlation between these methods was found in all circumstances.     

Sample-hold technique for analysis of respiratory gas composition at high breathing frequencies

A gas sampling device is described for continuous monitoring of respiratory gas composition that is applicable to experimental conditions when the breathing frequency is very high (greater than 2 Hz) and the response time of conventional gas analyzers becomes a critical limiting factor. The system utilizes the principle of discontinuous gas collection at any selected point of the respiratory cycle facilitated by ultraspeed piezoelectric valves and includes provision for sample-hold characteristics. Two distinct modes of operation are supported. In phase-locked mode gas sampling is synchronous with breathing frequency. In scanning mode gas collection is asynchronous with breathing frequency. Phase-locked mode may be used for continuous monitoring of end-tidal gas concentrations, whereas scanning mode is intended for assessing the gas concentration profile throughout the respiratory cycle. The system may be applied to steady breathing encountered in mechanical ventilation at high frequency or during quasi-steady breathing observed in panting animals. Combined with a respiratory mass spectrometer, the system has been used for measurement of gas concentrations in alveolar gas mixtures at breathing frequencies ranging from 3 to 30 Hz that were otherwise not amenable to rapid measuring techniques.     

Average thickness of the gas vesicle wall in Anabaena flos-aquae.

The average thickness of the layer of protein which forms the wall of the gas vesicles in Anabaena flos-aquae was estimated from measurements of their density and geometry. The volume of the gas space in a purified gas vesicle suspension was determined from the contraction which occurred when the gas vesicles were collapsed by pressure. The volume of the protein in the same sample was calculated from its dry weight and density. From knowledge of the geometry of the average gas vesicle the thickness of the protein layer, 1.54 nm, was then calculated. By a similar method the thickness of the Microcystis gas vesicle wall, 1.62 nm, was calculated from data published by others. The average thickness of the protein layer is, as expected, slightly less than the stacking periodicity of collapsed gas vesicle walls indicated by X-ray diffraction studies.Anabaena gas vesicles with a mean length of 494 nm have an average density of 0.119 mg μl^?1 1 mg of protein is present in gas vesicles having a, total volume of 8.43 μl and a gas space of 7.67 μl. Suspensions of isolated gas vesicles with a gas space concentration of 1 μl ml^?1 give a pressure-sensitive optical density, E_1cm (500 nm) of 2.72, but gas vacuoles in cells give a smaller value.     

Mathematical model of gas bubble evolution in a straight tube.

Deep sea divers suffer from decompression sickness (DCS) when their rate of ascent to the surface is too rapid. When the ambient pressure drops, inert gas bubbles may form in blood vessels and tissues. The evolution of a gas bubble in a rigid tube filled with slowly moving fluid, intended to simulate a bubble in a blood vessel, is studied by solving a coupled system of fluid-flow and gas transport equations. The governing equations for the fluid motion are solved using two techniques: an analytical method appropriate for small nondeformable spherical bubbles, and the boundary element method for deformable bubbles of arbitrary size, given an applied steady flow rate. A steady convection-diffusion equation is then solved numerically to determine the concentration of gas. The bubble volume, or equivalently the gas mass inside the bubble for a constant bubble pressure, is adjusted over time according to the mass flux at the bubble surface. Using a quasi-steady approximation, the evolution of a gas bubble in a tube is obtained. Results show that convection increases the gas pressure gradient at the bubble surface, hence increasing the rate of bubble evolution. Comparing with the result for a single gas bubble in an infinite tissue, the rate of evolution in a tube is approximately twice as fast. Surface tension is also shown to have a significant effect. These findings may have important implications for our understanding of the mechanisms of inert gas bubbles in the circulation underlying decompression sickness.     

Experimental studies on producer gas generation from wood waste in a downdraft biomass gasifier

A process of conversion of solid carbonaceous fuel into combustible gas by partial combustion is known as gasification. The resulting gas, known as producer gas, is more versatile in its use than the original solid biomass. In the present study, a downdraft biomass gasifier is used to carry out the gasification experiments with the waste generated while making furniture in the carpentry section of the institute’s workshop. Dalbergia sisoo, generally known as sesame wood or rose wood is mainly used in the furniture and wastage of the same is used as a biomass material in the present gasification studies. The effects of air flow rate and moisture content on biomass consumption rate and quality of the producer gas generated are studied by performing experiments. The performance of the biomass gasifier system is evaluated in terms of equivalence ratio, producer gas composition, calorific value of the producer gas, gas production rate, zone temperatures and cold gas efficiency. Material balance is carried out to examine the reliability of the results generated. The experimental results are compared with those reported in the literature.     

Modeling of Gas Production from Shale Reservoirs Considering Multiple Transport Mechanisms

Gas transport in unconventional shale strata is a multi-mechanism-coupling process that is different from the process observed in conventional reservoirs. In micro fractures which are inborn or induced by hydraulic stimulation, viscous flow dominates. And gas surface diffusion and gas desorption should be further considered in organic nano pores. Also, the Klinkenberg effect should be considered when dealing with the gas transport problem. In addition, following two factors can play significant roles under certain circumstances but have not received enough attention in previous models. During pressure depletion, gas viscosity will change with Knudsen number; and pore radius will increase when the adsorption gas desorbs from the pore wall. In this paper, a comprehensive mathematical model that incorporates all known mechanisms for simulating gas flow in shale strata is presented. The objective of this study was to provide a more accurate reservoir model for simulation based on the flow mechanisms in the pore scale and formation geometry. Complex mechanisms, including viscous flow, Knudsen diffusion, slip flow, and desorption, are optionally integrated into different continua in the model. Sensitivity analysis was conducted to evaluate the effect of different mechanisms on the gas production. The results showed that adsorption and gas viscosity change will have a great impact on gas production. Ignoring one of following scenarios, such as adsorption, gas permeability change, gas viscosity change, or pore radius change, will underestimate gas production.     

Effect of gas pressure in the root and stem base zone on methane transport through rice bodies

Ebullition of gas bubbles from the soil surface is, in some cases (e.g., in early growth stage of rice), one of the major pathways for methane transport from rice paddies to the atmosphere. However, the role of the gas phase (entrapped gas) in the paddy soil in plant-mediated methane transport, which is the major pathway for methane emission, has not been clarified. To clarify the effect of the gas phase below ground on the methane emission rate through rice plants, we partly exposed the root and stem base of hydroponically grown rice to a high concentration of methane gas at various gas pressures, and immersed the rest of the roots in a solution with a high methane concentration. The methane emission rate was measured from the top of the rice plant using a flow-through chamber method. The methane emission rate drastically increased with a small increase in gas pressure in the gas phase at the root and stem base zone, with about a 3 times larger emission rate being observed with 10 × 10^-3 atm of extra pressure (corresponding to 10 cm of standing water in rice paddy) compared to no extra pressure. However, when alginate was applied to the stem near the base to prevent contact with the gas phase, the methane emission rate did not increase with increasing gas pressure. On the other hand, from observations in the rice paddy, it was found that the gas is entrapped near the surface (e.g., at a depth of 1 cm) and the gas entrapped in the soil would come into direct contact with a part of the stem near the base of the rice plant. Thus, the gas entrapped in the soil could enter into the rice body directly from the part of the stem near the base which is beneath the soil surface due to gas pressure in the gas phase resulting from the pressure exerted by the standing water. Hence, this mechanism involving the entrapped gas could play an important role in methane emission from rice paddy by affecting the plant-mediated methane transport as well as ebullition of gas bubbles.     

Approaches to measuring fluxes of methane and nitrous oxide between landscapes and the atmosphere

The theory, applications, strengths and weaknesses of approaches commonly used for measuring trace gas fluxes are reviewed. Chambers, representing the smallest scale (～1 m²), are the most common tools. Their operating principle is simple, they can be highly sensitive, the cost can be low and field requirements small. Problems include leaks, stickiness of some gases, inhibition of fluxes through concentration build-up, pressure effects and spatial and temporal variability in gas fluxes. Mass balance techniques are suitable for small, defined source areas, typically tens to thousands of square metres in extent. Emissions are calculated from the difference in the rates at which the gas is carried into a control volume above the source area by the wind and carried out. The required primary data are profiles of gas concentration on the downwind boundaries as well as the wind speed profile, the wind direction and the upwind background gas concentration. They have been used to measure gas emissions from landfills, treated fields and small animal herds. Circular test areas make the method independent of wind direction. A newly developed technique based on a backward Lagrangian stochastic dispersion model is also applicable to small, well-defined source areas of any shape. The surface flux is calculated form measurements of atmospheric turbulence and stability and the gas concentration at any height downwind. Implementation of the method is aided greatly by a software package WindTrax. The combination provides a powerful new tool for measuring gas emissions from treated areas and intensive animal production systems. Finally, techniques suitable for measuring gas emissions on large landscape scales (ha) are discussed. Eddy covariance is the micrometeorologist’s preferred technique for this scale. The method uses fast response anemometers and gas sensors to make direct measurements of the vertical gas flux at a point, several times a second. However, it is not feasible for many trace gases for a variety of reasons. These are discussed. Relaxed eddy accumulation is an alternative technique that retains the attraction of eddy covariance by providing a direct point measurement. It removes the need for a fast response gas sensor by substituting for it a fast solenoid valve sampling system. Flux–gradient methods are in more common use. Fluxes are calculated as the product of an eddy diffusivity and the vertical concentration gradient of the gas or the product of a transfer coefficient and the difference in gas concentration between two heights. Assumptions of the method and precautions in its application are discussed.     

The Avoidance Response in Phycomyces

Phycomyces sporangiophores grow away from stationary objects, a phenomenon known as the avoidance response. Evidence is presented suggesting that a growth-stimulating gas is emitted from the sporangiophore and is then swept to the leeward side by air currents resulting in higher gas concentration on that side. The presence of a stationary barrier decreases the passive movement of the gas away from the leeward side. It is proposed that an increase of this gas on one side causes that side to grow faster. Indirect evidence suggests that the gas is water vapor.     

The secretion of inert gas into the swim-bladder of fish

The composition of the gas mixture secreted into the swim-bladders of several species of fish has been determined in the mass spectrometer. The secreted gas differed greatly from the gas mixture breathed by the fish in the relative proportions of the chemically inert gases, argon, neon, helium, and nitrogen. Relative to nitrogen the proportion of the very soluble argon was increased and the proportions of the much less soluble neon and helium decreased. The composition of the secreted gas approaches the composition of the gas mixture dissolved in the tissue fluid. A theory of inert gas secretion is proposed. It is suggested that oxygen gas is actively secreted and evolved in the form of minute bubbles, that inert gases diffuse into these bubbles, and that the bubbles are passed into the swim-bladder carrying with them inert gases. Coupled to a preferential reabsorption of oxygen from the swim-bladder this mechanism can achieve high tensions of inert gas in the swim-bladder. The accumulation of nearly pure nitrogen in the swim-bladder of goldfish (Carassius auratus) is accomplished by the secretion of an oxygen-rich gas mixture followed by the reabsorption of oxygen.     

Influence of Bohr-Haldane effect on steady-state gas exchange

The influence of the Bohr-Haldane effect (BH) on steady-state gas exchange has previously been described by its effect of gas transfer from the blood when arterial and venous blood gas tensions were held constant. This report quantifies by computer analysis the effects of BH when either or both arterial and venous blood gas tensions are subject to change. When mixed venous blood gas composition is held constant, elimination of BH from a single lung unit typically reduces CO2 output by 6.5% and O2 uptake by 0.5%. Similar effects occur in a two-compartment lung model whether alveolar ventilation-perfusion (VA/Q) mismatch occurs in a parallel or series ventilatory arrangement. When arterial blood gas composition is held constant, elimination of BH increases systemic venous CO2 partial pressure, but O2 partial pressure is hardly affected in the absence of metabolic acidosis. When both mixed venous and arterial blood gas tensions vary and gas exchange is stressed by VA/Q inequality, altitude, anemia, or exercise, elimination of BH predominantly affects mixed venous rather than arterial blood gas tensions. it is concluded that BH may act primarily to reduce tissue acidosis.     

Anomalous behaviour of forward and perpendicular light scattering of a cyanobacterium owing to intracellular gas vacuoles

Extinction, absorption, and forward and perpendicular light scatter of the blue-green alga Microcystis aeruginosa with different amounts of intracellular gas vacuoles were determined. The amount of gas vacuoles in the cells was controlled by application of pressure. The presence of the gas vacuoles caused a tenfold increase in perpendicular light scatter, and a fivefold decrease in forward light scatter as measured by flow cytometry. Chlorophyll fluorescence showed a 16% decrease. The presence of gas vacuoles did not affect the size of the algae. The absorption spectrum of Microcystis aeruginosa was slightly raised but practically not distorted by the gas vacuoles. The attenuation spectrum, a measure for light extinction by the algal cells, was significantly distorted. The increase of perpendicular light scatter intensity of the cells is a direct consequence of the relatively high scatter of each vacuole, whereas the forward light scatter decrease is attributed to a lower phase-shift factor rho of the whole cells, caused by the intact gas vacuoles.     

Into the Voids: The Distribution, Function, Development and Maintenance of Gas Spaces in Plants

Gas spaces are a common but frequently overlooked componentof most embryophytes, and of several brown macroalgae. Theyhave many functions, but in vascular land plants the predominantfunction is that of gas distribution. In aquatic macrophytesbuoyancy is a significant function of gas spaces. The developmentof gas spaces can occur without contact with an external gasphase. Schizogenous gas spaces develop within tissues by mechanismswhich involve pre-programmed separation of middle lamellae atthe corners of cells, frequently followed by more widespreadseparation. In both cases there is replacement of the resultingvacuum plus water vapour with gases which were dissolved inthe water of adjacent cells. Lysigenous gas spaces are producedin a similar way but with cell lysis following and perhaps replacingseparation of middle lamellae, and the need for removal of waterand solutes into adjacent cells. Maintenance of gas spaces involvesa combination of absence of invasion with liquid water and maintenanceof hydrophobic surfaces around the gas spaces. This glib summaryof the formation and maintenance of gas spaces covers many aspectsof these phenomena which need further investigation. gas spaces; lysigenous spaces; ontogeny; phylogeny; schizogenous spaces     

Comparative Study of the Structure of Gas Vacuoles

The fine structure of gas vacuoles was examined in two blue-green algae, two green bacteria, three purple sulfur bacteria, and two halobacteria. The gas vacuole is a compound organelle, composed of a variable number of gas vesicles. These are closed, cylindrical, gas-containing structures with conical ends, about 80 to 100 nm in width and of variable length, ranging from 0.2 to over 1.0 mum. The wall of the gas vesicle is a non-unit membrane 2 to 3 nm in thickness, bearing very regular striations with a periodicity of 4 nm, oriented more or less at right angles to the long axis of the cylinder. This fine structure could be clearly resolved in isolated gas vesicles prepared from a blue-green alga and from Halobacterium halobium, and its presence in the gas vesicles of the green bacterium Pelodictyon clathratiforme was inferred from thin sections. The gas vacuole thus appears to be a homologous organelle in all of these procaryotic groups. Minor differences with respect to the length and arrangement of the gas vesicles were observed. In blue-green algae and green bacteria, the vesicles are relatively long and tend to be arrayed in parallel bundles; in purple sulfur bacteria and Halobacterium, they are shorter and more irregularly distributed in the cell.     

Fermentation of biomass-generated producer gas to ethanol

The development of low-cost, sustainable, and renewable energy sources has been a major focus since the 1970s. Fuel-grade ethanol is one energy source that has great potential for being generated from biomass. The demonstration of the fermentation of biomass-generated producer gas to ethanol is the major focus of this article in addition to assessing the effects of producer gas on the fermentation process. In this work, producer gas (primarily CO, CO(2), CH(4), H(2), and N(2)) was generated from switchgrass via gasification. The fluidized-bed gasifier generated gas with a composition of 56.8% N(2), 14.7% CO, 16.5% CO(2), 4.4% H(2), and 4.2% CH(4). The producer gas was utilized in a 4-L bioreactor to generate ethanol and other products via fermentation using a novel clostridial bacterium. The effects of biomass-generated producer gas on cell concentration, hydrogen uptake, and acid/alcohol production are shown in comparison with "clean" bottled gases of similar compositions for CO, CO(2), and H(2). The successful implementation of generating producer gas from biomass and then fermenting the producer gas to ethanol was demonstrated. Several key findings following the introduction of producer gas included: (1) the cells stopped growing but were still viable, (2) ethanol was primarily produced once the cells stopped growing (ethanol is nongrowth associated), (3) H(2) utilization stopped, and (4) cells began growing again if "clean" bottled gases were introduced following exposure to the producer gas.     

Aerobic degradation of toluene in a closed chemostat with and without a head space outlet

The present paper describes the continuous aerobic cultivation of a Pseudomonas strain with toluene as the substrate in a closed chemostat with oxygen or air as the gas phase. Due to the constant supply of a nitrogen-saturated aqueous medium, nitrogen passes from the liquid phase of the chemostat into the gas phase (head space). This results in an increasing nitrogen content (asymptotic approach to 100%). The concomitant decrease in the partial pressure of the oxygen in the gas phase finally leads to an oxygen limitation for the bacteria in the medium and an incomplete toluene degradation. The critical nitrogen content of the gas phase at which oxygen limitation begins depends on the toluene concentration in the incoming medium. However, when the gas is continuously removed from the head space, the nitrogen content reaches a steady-state value of less than 100%, depending on the flow rate of the outgoing gas. The oxygen limitation and the associated incomplete toluene degradation can be prevented in this way. The method of gas removal from the head space to avoid oxygen limitation is also applicable when the reactor is supplied with air instead of oxygen. Waste waters contaminated with highly volatile pollutants can thus be biologically decontaminated under aerobic conditions, without shifting the pollution problem from the liquid to the gas phase.     

Automatic gas tank switching system for CO2 incubators.

The use and construction of an automatic gas tank switching system are described. This device monitors the gas pressure in a CO2 incubator gas system and automatically switches to a reserve tank when the main supply tank is depleted. The unit contains an alarm system that signals either loss of power or gas pressure in the supply system.     

The Physics of Gas Exchange Across the Avian Eggshell

The principles which govern gas exchange by diffusion acrossthe pores of the avian eggshell are reviewed and compared withconvective gas exchange. The concept of conductance is definedfor both diffusive and convective gas exchange through pores,and methods of calculating pore size are described. Estimatesof conductances of the elements in the gas transfer path fromatmosphere to chorioallantoic capillary blood are discussed,and recent studies on the role of ternary diffusion and a convectivecomponent to gas fluxes are presented.