高瓦斯矿发火区封闭时对瓦斯爆炸界限因素的影响

针对高瓦斯矿发火区封闭时常发生瓦斯爆炸事故,对影响瓦斯爆炸界限的因素进行实验,探索温度、压力、可燃气体(CO)、惰性气体(N2和CO2)等条件对瓦斯爆炸界限的影响规律。得出常温常压下瓦斯爆炸的体积分数下限为5%,瓦斯爆炸上限为13.5%,以及CO2的惰化效果比N2更好的结论。根据实验数据绘制混合气体的爆炸三角形,并进行新的惰化分区划分,不仅为火区封闭时防治瓦斯爆炸提供新的技术途径,而且能计算出使火区惰化时,所需惰性气体量,可对这些因素进行合理控制,有效地降低瓦斯爆炸危险性。     

Detonation formation in H $_2$-O $_2$/He/Ar mixtures at elevated initial pressures

In this paper the formation of detonation in H-O/He/Ar mixtures at elevated initial pressures was investigated in an initiation tube for a detonation driver with an exploding wire as the ignition source. In most experiments the detonation wave was formed by a DDT process in which a reactive shock wave accelerates behind the leading shock wave and eventually leads to the onset of detonation. The onset position was found to be at the leading shock wave or behind it. Only in very sensitive mixtures at high initial pressure the direct initiation of detonation was observed. The influence of ignition energy, initial pressure and composition on the detonation induction distance was determined. The results show that the detonation induction distance increases with the decrease of ignition energy and initial pressure and with the increase of the mole fraction of helium or argon. With the same mole fraction, argon increases the induction distance more than helium. In the facility utilized the DDT upper and lower limits of hydrogen in H-O mixtures are in the ranges from 36 to 40 % and from 78 to 82 %, respectively, and the upper limits for helium and argon in stoichiometric H-O mixtures are 40 % and 36 %, respectively. High pressure peaks generated by the DDT process were measured, especially in mixtures near the DDT limits. Statistical results show that such peak pressures can be up to 6 times of the CJ-pressures. Received 1 March 2000 / Accepted 25 May 2000     

Two-cell detonation: losses effects on cellular structure and propagation in rich H2–NO2/N2O4–Ar mixtures

Detonation experiments in H₂–NO₂/N₂O₄–Ar mixtures (Equivalence ratio 1.2 and initial pressure lower than 0.1 MPa) confined in a tube of internal diameter 52 mm reveal two propagation regimes depending on initial pressure: (1) a quasi-CJ regime is observed along with a double cellular structure at high pressures; (2) at lower pressures, a low velocity detonation regime is observed with a single structure. Transition between this two regimes happens when the spinning detonation of the larger cell vanishes. Each detonation regime is characterized by velocity and pressure measurements and cellular structure records. Coherence between all experimental data for each experiment leads in assumption that losses are responsible for the transition between one regime to another. In a second part, we study such behaviour for a two-step mixture through numerical simulations using a global two-step chemical kinetics and a simple losses model. Numerical simulations qualitatively agree with experiments. Both detonation regimes with their own cellular structures are reproduced.     

Flow of rarefied gases in a capillary screen at different temperatures

An experimental study was made of the flow of the gases He, Ne, Ar, Kr, Xe, H₂, D₂, N₂, CO₂, and CH₄ in the range of Knudsen numbers of 10⁴–10^?1 at room temperature in a capillary screen. A study was also made of the flow of a number of inert and diatomic gases at temperatures of 77.2 and 194.7 °K in an orifice and in a capillary screen. The relative flow rates were determined in the free-molecular mode of flow. The coefficients of accomodation of tangential momentum are calculated for the gases studied at different temperatures.     

Comparison of critical conditions for DDT in regular and irregular cellular detonation systems

Abstract. The results of an experimental study of DDT in mixtures with regular and irregular detonation cellular structures are presented. Experiments were carried out in a tube 174 mm i. d. with obstacles (blockage ratios were 0.1, 0.3, and 0.6). Mixtures used were hydrogen–air and stoichiometric hydrogen–oxygen diluted with , Ar, and He. The critical conditions for DDT are shown to depend on the regularity of the cellular structure of test mixtures. The critical values of the cell sizes in Ar- and He-diluted mixtures are shown to be significantly smaller than those in -diluted mixtures. This means that systems with a highly regular detonation cellular structure have far less capacity for undergoing DDT compared to irregular ones with the same values of detonation cell sizes. Received 18 November 1999 / Accepted 15 May 2000     

Some properties of strongly nonequilibrium flows with population inversion in shock waves

The effect of incident flow parameters and composition of a CO₂ + N₂ + H₂O(He) mixture on population inversion in the relaxation zone of a normal shock wave is considered.     

Impact of Capillary Pressure, Salinity and In situ Conditions on CO2 Injection into Saline Aquifers

This article presents a numerical investigation of the combined effects of capillary pressure, salinity and in situ thermodynamic conditions on CO₂-brine-rock interactions in a saline aquifer. We demonstrate that the interrelations between capillary pressure, salinity, dissolution and drying-out affect CO₂ injectivity and storage capacity of a saline aquifer. High capillary forces require a high injection pressure for a given injection rate. Depending on salinity, the increase in injection pressure due to capillary forces can be offset by the dissolution of CO₂ in formation water and its compressibility. Higher capillary forces also reduce gravity segregation, and this gives a more homogeneous CO₂ plume which improves the dissolution of CO₂. The solubility of CO₂ in formation water decreases with increasing salinity which requires an increased injection pressure. Higher salinity and capillary pressure can even block the pores, causing an increased salt precipitation. Simulations with various pressure-temperature conditions and modified salinity and capillary pressure curves demonstrate that, with the injection pressures similar for both cold and warm basins at a given injection rate, CO₂ dissolves about 10% more in the warm basin water than in the cold basin. The increase in dissolution lowers the injection pressure compensating the disadvantage of low CO₂ density and compressibility for storage in warm basins.     

Detonation wave initiated by explosive condensation of supersaturated carbon vapor

An experimental study of the influence of condensation of supersaturated carbon vapor formed behind reflected shock waves on the process of propagation of a shock wave and formation of a detonation wave of condensation is carried out. Highly supersaturated carbon vapor was formed from thermal decay of unstable carbon suboxide C₃O₂ → C + 2CO behind a shock wave in mixtures containing 10–30% C₃O₂ in Ar. This reaction was followed by fast growth of condensed carbon particles, accompanied by heat release. Experiments have shown a considerable temperature and pressure increase in the narrow zone behind the wave front, resulting in shock wave amplification and transition to a detonation-like regime. An analysis of the kinetics and heat release in the given conditions and calculations based upon one-dimensional detonation theory have shown that in a mixture of 10% C₃O₂ + Ar, insufficient heat release resulted in a regime of “overdriven detonation”. In a mixture of 20% C₃O₂ + Ar a very good coincidence of measured values of pressure and wave velocity with calculated Chapman–Jouguet parameters is observed. In a 30% C₃O₂ + Ar mixture, an excess heat release caused a slow down of the effective condensation rate and a regime of “underdriven detonation” is observed.     

CH4-O2 混合气中爆燃爆震转捩的数值模拟

运用化学流体力学基本理论和两步燃烧反应模型原理，建立了一维封闭体系可燃气爆燃爆震转变现象的数学模型，利用拉格朗日质量坐标变换下的Ｌａｘ－Ｗｅｎｄｒｏｆ和Ｍｅｃｏｒｍｉｃ气动差分与Ａｄａｍｓ化学差分格式，求解基本方程，成功地完成了过程的数值模拟，清楚地说明了可燃气中ＤＤＴ现象由压缩波到激波达到稳态爆震的发生机制和火焰带引生爆震波的过程行为。     

Characteristics of Salt-Precipitation and the Associated Pressure Build-Up during CO<Subscript>2</Subscript> Storage in Saline Aquifers

Mitigation and control of borehole pressure at the bottom of an injection well is directly related to the effective management of well injectivity during geologic carbon sequestration activity. Researchers have generally accepted the idea that high rates of CO₂ injection into low permeability strata results in increased bottom-hole pressure in a well. However, the results of this study suggested that this is not always the case, due to the occurrence of localized salt precipitation adjacent to the injection well. A series of numerical simulations indicated that in some cases, a low rate of CO₂ injection into high permeability formation induced greater pressure build-up. This occurred because of the different types of salt precipitation pattern controlled by buoyancy-driven CO₂ plume migration. The first type is non-localized salt precipitation, which is characterized by uniform salt precipitation within the dry-out zone. The second type, localized salt precipitation, is characterized by an abnormally high level of salt precipitation at the dry-out front. This localized salt precipitation acts as a barrier that hampers the propagation of both CO₂ and pressure to the far field as well as counter-flowing brine migration toward the injection well. These dynamic processes caused a drastic pressure build-up in the well, which decreased injectivity. By modeling a series of test cases, it was found that low-rate CO₂ injection into high permeability formation was likely to cause localized salt precipitation. Sensitivity studies revealed that brine salinity linearly affected the level of salt precipitation, and that vertical permeability enhanced the buoyancy effect which increased the growth of the salt barrier. The porosity also affected both the level of localized salt precipitation and dry-out zone extension depending on injection rates. High temperature injected CO₂ promoted the vertical movement of the CO₂ plume, which accelerated localized salt precipitation, but at the same time caused a decrease in the density of the injected CO₂. The combination of these two effects eventually decreased bottomhole pressure. Considering the injectivity degradation, a method is proposed for decreasing the pressure build-up and increasing injectivity by assigning a ‘skin zone’ that represents a local region with a transmissivity different from that of the surrounding aquifer.     

Gas Sorption and the Consequent Volumetric and Permeability Change of Coal I: Experimental

Experimental and numerical investigations were conducted to study adsorption and desorption of pure and multicomponent gas on coal, and the sorption-induced volumetric strain and permeability change of the coal. This paper presents the experimental work. Using CO \(_2\) , N \(_2\) , and CO \(_2\) and N \(_2\) binary mixtures of different composition as injection gases, the measurements were conducted on a cylindrical composite coal core at varying pore pressures and constant effective confining pressure. Sorption was measured using a volumetric method. The initial and equilibrium system pressure and gas phase composition were measured. The total amount of adsorption and the composition of the adsorbed phase (for adsorption of binary gas mixtures) were calculated based on material balance. During the process of sorption, the volume of the core was monitored by recording the volume of the water in the confining pressure vessel. Sorption-induced strain was calculated as the ratio of the sorption-induced volumetric change to the initial volume of the core. After adsorption equilibrium was reached, the permeability of the core was measured based on the Darcy equation for gas flow. Sorption and permeability measurements were conducted for each test gas at first increasing and then decreasing pressures. Volumetric strain was only measured while pore pressure increased. To our knowledge, this is the first study measuring adsorption, volumetric strain, and permeability on the same piece of core with the same apparatus.     

A Pore Scale Study of Non-Newtonian Effect on Foam Propagation in Porous Media

CO₂ injection is one of the most promising techniques to enhance oil recovery. However, an unfavorable mobility ratio, reservoir heterogeneity and gravity segregation can reduce the macroscopic sweep efficiency. In situ foaming of injected CO₂ is the method that has the most potential for improving sweep efficiency based on controlling CO₂ mobility. This study investigates the foaming behavior of N,N,N′-trimethyl-N′-tallow-1,3-diaminopropane (DTTM) surfactant with CO₂ in a transparent porous microflow model with natural rock pore structures. It focuses on the effect of the salinity induced non-Newtonian behavior of DTTM solution on foam propagation. The performance of foams stabilized by 0.5 wt% DTTM solution over the viscosity range from 0.71 (at 5 wt% NaCl) to 41 cp (at 20 wt% NaCl) was compared with conventional polymer-enhanced foams whose liquid phase contained a commonly used foaming surfactant, C15–18 Internal Olefin Sulfonate (C15–18 IOS) and a hydrolyzed polyacrylamide. Such comparisons have also provided insight into the respective impacts of liquid phase viscosification by worm-like surfactant micelles and polymer on foam texture associated with its rheological characteristics. It was found that at low aqueous phase viscosity (injection liquid viscosity of 0.71 cp) the maximum achievable viscosity of DDTM foam was around 1000 cp, which was 80 times IOS stabilized foam. The interfacial tension of DTTM was higher than that of IOS, resulting coarser foam texture and higher individual lamella resistance. An increase in DTTM solution viscosity by a factor of 33 decreased foam generation and viscosity for gas injection. This was not observed for the simultaneous injection of gas and DTTM solution. Overall, the effect of liquid phase viscosity on transient foam behavior during gas injection is similar for both DTTM and IOS regardless of the difference in the nature of viscosifying agents (WLM vs 3330 s polymer). An increase in gas injection pressure without liquid injection delayed foam propagation and reduced the magnitude of foam viscosity. The results from this study indicated that DTTM surfactant is an important alternative to commercially available polymers that have been used to enhance foam performance in porous media. This particular surfactant type also overcomes several disadvantages of polymers such as limited temperature and salinity tolerance, shear degradation, and filtering in low permeability formations.

     

Population inversion behind a detonation wave propagating in a variable-density medium

The creation of an active medium by means of detonation has been investigated on a number of occasions. It was suggested that one could use the expansion of the detonation products of an acetylene-air mixture in vacuum [1] or the cooling of the detonation products of a mixture of hydrocarbons and air through a nozzle [2, 3]. In [4], the detonation of a solid high explosive was used to produce population inversion in the gas mixture CO₂-N₂-He(H₂O). Stimulated emission from HF molecules was observed in [5] behind the front of an overdriven detonation wave propagating in an F₂-H₂-Ar mixture in a shock tube. Population inversion behind a detonation wave was studied in H₂-F₂-He mixtures in [6–8] and in H₂-Cl₂-He mixtures in [9] with energy release on a plane and on a straight line in a medium with constant density. Similar problems were solved for shock waves propagating in both a homogeneous gaseous medium [7, 10] and in the supersonic part of an expanding nozzle. In the present paper, we study theoretically population inversion behind an overdriven detonation wave propagating in a mixture (fine carbon particles + acetylene + air) which flows through a hypersonic nozzle. The propagation of detonation in media with variable density and initial velocity was considered, for example, in [11, 12]. Analysis of the gas parameters behind a detonation wave propagating in a medium with constant density (for a given fuel) showed that the temperature difference across the detonation front is insufficient to produce population inversion of the vibrational levels of the CO₂ molecule.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 1, pp. 65–71, January–February, 1980.I am grateful to V. P. Korobeinikov for a helpful discussion of the results.     

Injection of Acid Gas Mixtures in Sour Oil Reservoirs: Analysis of Near-Wellbore Processes with Coupled Modelling of Well and Reservoir Flow

The reinjection of sour or acid gas mixtures is often required for the exploitation of hydrocarbon reservoirs containing remarkable amounts of acid gases (H₂S and CO₂) to reduce the environmental impact of field exploitation and provide pressure support for enhanced oil recovery (EOR) purposes. Sour and acid gas injection in geological structures can be modelled with TMGAS, a new Equation of State (EOS) module for the TOUGH2 reservoir simulator. TMGAS can simulate the two-phase behaviour of NaCl-dominated brines in equilibrium with a non-aqueous (NA) phase, made up of inorganic gases such as CO₂ and H₂S and hydrocarbons (pure as well as pseudo-components), up to the high pressures (~100 MPa) and temperatures (~200°C) found in deep sedimentary basins. This study is focused on the near-wellbore processes driven by the injection of an acid gas mixture in a hypothetical high-pressure, under-saturated sour oil reservoir at a well-sector scale and at conditions for which the injected gas is fully miscible with the oil. Relevant-coupled processes are simulated, including the displacement of oil originally in place, the evaporation of connate brine, the salt concentration and consequent halite precipitation, as well as non-isothermal effects generated by the injection of the acid gas mixture at temperatures lower than initial reservoir temperature. Non-isothermal effects are studied by modelling in a coupled way wellbore and reservoir flow with a modified version of the TOUGH2 reservoir simulator. The described approach is limited to single-phase wellbore flow conditions occurring when injecting sour, acid or greenhouse gas mixtures in high-pressure geological structures.     

On the compression process in a free-piston shock-tunnel

Preliminary results in the Marseille free-piston shock-tunnel facility are presented. The compression of the driver gas by the piston is studied experimentally for two different geometries of the end of the compression tube. Peak pressures obtained with the end of the compression tube closed, and with bursting of the diaphragm separating the high pressure from the low pressure chamber, are compared with calculated values in the cases of N₂ and He as driver gases. A phenomenon of accoustic resonance has been uncovered, generating strong pressure oscillations which, if not properly dealt with, could impair the quality of the useful flow in such a facility.This article was processed using Springer-Verlag T_EX Shock Waves macro package 1.0 and the AMS fonts, developed by the American Mathematical Society.     

An Experimental Study of CO<Subscript>2</Subscript> Exsolution and Relative Permeability Measurements During CO<Subscript>2</Subscript> Saturated Water Depressurization

Dissolution of CO₂ into brine is an important and favorable trapping mechanism for geologic storage of CO₂. There are scenarios, however, where dissolved CO₂ may migrate out of the storage reservoir. Under these conditions, CO₂ will exsolve from solution during depressurization of the brine, leading to the formation of separate phase CO₂. For example, a CO₂ sequestration system with a brine-permeable caprock may be favored to allow for pressure relief in the sequestration reservoir. In this case, CO₂-rich brine may be transported upwards along a pressure gradient caused by CO₂ injection. Here we conduct an experimental study of CO₂ exsolution to observe the behavior of exsolved gas under a wide range of depressurization. Exsolution experiments in highly permeable Berea sandstones and low permeability Mount Simon sandstones are presented. Using X-ray CT scanning, the evolution of gas phase CO₂ and its spatial distribution is observed. In addition, we measure relative permeability for exsolved CO₂ and water in sandstone rocks based on mass balances and continuous observation of the pressure drop across the core from 12.41 to 2.76 MPa. The results show that the minimum CO₂ saturation at which the exsolved CO₂ phase mobilization occurs is from 11.7 to 15.5%. Exsolved CO₂ is distributed uniformly in homogeneous rock samples with no statistical correlation between porosity and CO₂ saturation observed. No gravitational redistribution of exsolved CO₂ was observed after depressurization, even in the high permeability core. Significant differences exist between the exsolved CO₂ and water relative permeabilities, compared to relative permeabilities derived from steady-state drainage relative permeability measurements in the same cores. Specifically, very low CO₂ and water relative permeabilities are measured in the exsolution experiments, even when the CO₂ saturation is as high as 40%. The large relative permeability reduction in both the water and CO₂ phases is hypothesized to result from the presence of disconnected gas bubbles in this two-phase flow system. This feature is also thought to be favorable for storage security after CO₂ injection.     

Competitive Methane Desorption by Supercritical CO2 Injection in Coal

A large diameter (∼70 mm) dry coal sample was used to study the competitive displacement of CH₄ by injection of supercritical CO₂, and CO₂–CH₄ counter-diffusion in coal matrix. During the test, a staged loading procedure, which allows the calibration of the key reservoir modelling parameters in a sequential and progressive manner, was employed. The core-flooding test was history matched using an Enhanced Coalbed Methane (ECBM) simulator, in which Fick’s Law for mixed gas diffusion and the extended Langmuir equations are implemented. The system pressure rise during the two loading stages and the CO₂ breakthrough time in the final production stage were matched by using the pair of constant sorption times (9 and 3.2 days) for CH₄ and CO₂, respectively. The corresponding diffusion coefficients for CH₄ and CO₂ were estimated to be 1.6 ×  10⁻¹² and 4.6 ×  10⁻¹² m²/s, respectively. Comparison was made with published gas diffusion coefficients for dry ground samples (ranging from < 0.063 to ∼3 mm) of the same coal at relatively low pressures (< 4 MPa). The CO₂/CH₄ gas diffusion coefficient ratio was well within the reported range (2–3), whereas the CH₄ diffusion coefficient obtained from history matching of the core-flooding test is approximately 15 times smaller than that arrived by curve-fitting the measured sorption uptake rate using a unipore diffusion model. The calibrated model prediction of the effluent gas composition was in good agreement with the test data for CO₂ mole fraction of up to 20%.     

Transition from fast deflagration to detonation under the influence of periodic longitudinal perturbations

A computational and experimental investigation have been carried out to study deflagration to detonation transition under the influence of periodic longitudinal perturbations. The fast deflagration prior to transition is obtained by suppressing the oscillatory structure of a detonation first. In the one-dimensional computational study, the subsequent re-transition is stimulated using periodic density perturbations. The optimal perturbation period to induce transition is of the order of the rea ction time of the detonation structure. In the experiments, re-transition is stimulated using periodic wire screens placed across the channel. The gas mixture used is 2C₂H₂+5O₂+75%Ar. Laser stroboscopic photography showed the generation of longitudinal pressure waves as the leading shock passes through the wire screens. The interactions of the pressure waves with the leading shock and the reaction zone establish coupling for transition to occur. The computational and experimental studies showed that the time required for transition to take place is dependent on the frequency of the applied perturbation. The present results indicate the need to examine deflagration to detonation transition from the point of view of the formation of an organized oscillatory system.     

Inverted population of Co2 molecules in expanding gas streams

The system of equations of hydrodynamics, which describes the process of escape of the mixtures CO₂ + N₂ + He, H₂O from a nozzle, is solved numerically in conjunction with the equations of the kinetics of the excitation of the vibrational degrees of freedom of the molecules. It is found that an inverted population of the CO₂ molecules with respect to the transition [00 °1] – [10 °0], is produced under certain conditions at the exit from the nozzle. The magnitude of the inversion depends both on the nozzle configuration and on the initial values of the gas temperature and pressure. It is shown that for a specified nozzle configuration there exist optimal values of these parameters, at which the inverted population of the CO₂ molecules reaches approximately 10¹⁵ cm^–3.Translated from Zhumal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 5, pp. 24–34, September–October, 1971.