温度和围压耦合作用下煤样渗透率变化的试验研究

为了探究不同温度和围压耦合影响下的煤样渗透率变化特征,选用甘肃新北矿区低变质程度的烟煤,采用实验室试验的方法,借助Quanta TM 250扫描电子显微镜、Auto Pore IV 9500全自动压汞仪、Autosorb-1型全自动比表面和孔径分布分析仪,对煤样的内外部孔隙特征进行了测试分析;采用自主搭建的瓦斯渗流测定装置,对不同温度和围压耦合条件下的原煤瓦斯渗流进行了测定。结果表明:在试验采用的温度、围压变化范围(25~80℃,3~9 MPa)内,所测得的16组煤样渗透率均表现出了较强的温度、压力敏感性,围压对渗透率的影响明显高于温度对渗透率的影响;随着温度和围压的增大,渗透率呈减小趋势,而且减小趋势逐渐放缓,变化符合幂函数关系;温度与围压耦合时对煤样渗透率的影响显著,渗透率的变化服从指数分布。

基于底板高渗砂岩的裂隙瓦斯截流抽采技术

针对唐家河煤矿384采区底板砂岩中的裂隙瓦斯在底板裂隙水疏排之后上溢造成31847工作面和巷道瓦斯超限的实际问题,提出了截流抽采采区底板砂岩裂隙瓦斯的治理技术。通过在31847机巷施工63°大俯角下行穿层钻孔,对穿透384采区底板砂岩上溢的裂隙瓦斯进行截流抽采,并通过数值模拟确定了截流钻孔的合理间距为8 m。应用结果表明,施工截流钻孔后,工作面回风瓦斯浓度始终控制在0.8%以内,同时在瓦斯治理过程中截流抽采了约69.12万m3的裂隙瓦斯,彻底消除了31847工作面瓦斯超限的隐患。

低透气煤层高压气水混压增透驱替瓦斯技术研究

针对煤体纳米级孔隙内瓦斯难以解吸抽采的难题,首次提出了低透气煤层高压气水混压增透驱替瓦斯技术,研究指出高压气水混压增透驱替原理主要包括压裂裂隙的形成、水分竞争吸附置换瓦斯和高压空气驱替提高运移效率并解堵3个核心部分。研发了高压气水混压增透驱替瓦斯技术配套工艺及装备。在绿水洞煤矿K1煤层进行了现场试验,试验结果表明:矿井的平均单孔瓦斯抽采纯量从2.43 L/min提高到6.45 L/min,增加了2.65倍,平均抽采浓度从31.3%提到47.6%,增加了16.3%,煤层瓦斯含量降低了25.14%~80.62%,取得了显著的效果。

动静载荷耦合作用下复合煤岩体的力学特性及破坏特征

为了弄清瓦斯爆炸与煤岩动力灾害下巷道失稳破坏的机制,利用MTS伺服压力机和霍普金森压杆系统,研究了复合煤岩体在静态和动态载荷下的破坏特征,以及煤岩厚度比例、煤岩组合角度和冲击方向对煤岩体力学性能和破坏形式的影响。试验采用高和直径均为50 mm的圆柱形试样,选取烟煤和砂岩为实验材料。试验设置的煤岩厚度比例分别为0∶1,1∶2,1∶1,2∶1和1∶0,煤岩组合角度分别为0°,15°,30°,45°,60°和90°。在动态冲击试验中,分别设置冲击煤样和冲击岩样2种载荷施加方向,来观察冲击方向对复合煤岩体力学性能的影响。研究结果表明:煤岩厚度比例越高,复合煤岩体的抗压强度和弹性模量越小;随着组合角度的增加,复合煤岩体的弹性模量逐渐增加,弹性模量最大的组合角度为90°,弹性模量最小的角度为0°;抗压强度先减小后增加,组合角度为45°时,抗压强度最小,组合角度为90°时,抗压强度最大。与冲击煤样相比,冲击岩样时复合煤岩体的抗压强度和弹性模量较大,极限应变略低。在单轴加载下,复合试样组合角度小于45°时主要以劈裂破坏为主,45°时劈裂破坏和压剪破坏并存,大于45°时为沿交界面的剪切破坏。在动态载荷下,45°角的应力-应变曲线由于煤岩接触面滑移没有出现回弹现象,且此时动态抗压强度最小。

注热蒸汽后的煤体微观孔裂隙演化规律

我国煤层瓦斯赋存具有强吸附、低渗透、微孔隙的特点,注热蒸汽开采作为一种新的增加瓦斯抽采率的方法,存在的热蒸汽作用于煤体后的瓦斯解吸、孔隙结构改变等一些基础问题仍未探讨。为了揭示热蒸汽对煤体孔裂隙结构的影响作用,使用高温热蒸汽对煤样进行处理,并借助扫描电镜、压汞法和核磁共振测试手段探讨了热处理前后煤样的孔裂隙演化规律。试验结果表明:热蒸汽作用后的煤体孔隙结构演化归结为4种基本模式,分别为孔隙扩张模式、孔隙连通模式、孔隙破裂模式和裂隙贯通模式。热蒸汽处理后,2种煤样进退汞差值均变大,总孔容、渗透率、孔隙率和平均孔径得到了显著提升;表明蒸汽作用后煤开放孔变多,闭合孔和半闭合孔减少,T2谱中的波峰P1、P2和弛豫时间、整体峰谱面积均有显著提高,表明蒸汽作用后煤孔隙结构受热效应、水蒸气疏孔的影响,孔隙由中小孔向中大孔转变,孔裂隙连通性增加。原有的孔隙得到了进一步发育,孔隙结构的改变能促进煤体的扩孔增渗,最终有利于瓦斯在煤体内的解吸与渗流。对于注热增渗等技术的的进一步发展具有较好的基础作用,研究内容为下一步蒸汽作用后瓦斯解吸研究有很好的指导作用,为注热蒸汽提高煤层渗透率,进而提高煤层气抽采率提供了依据。

高预应力与爆炸载荷耦合作用下的巷道围岩损伤破坏机制

近年来我国煤矿安全得到一定改善,但是瓦斯爆炸事故没有从根本上消除,依然是煤矿事故的重中之重。煤矿深部巷道发生的瓦斯爆炸造成的事故损伤巨大,爆炸冲击不仅造成人员伤亡,同时也造成巷道坍塌,这主要是因为高预应力和爆炸载荷的耦合作用。为了研究高预应力损伤与瓦斯爆炸载荷耦合作用下巷道围岩损伤规律以及多种载荷叠加的作用机制,基于ANSYS/LS-DYNA数值模拟软件,采用隐-显式耦合分析方法,模拟了0,5,10和15 MPa初始地应力和爆炸载荷耦合作用下巷道围岩的动态响应特征,通过研究巷道预应力损伤和位移的变化以及预应力与爆炸载荷耦合下损伤、位移和应力的变化,得出以下研究结果:在无地应力下,巷道几乎没有预应力损伤和初始位移,随着地应力的增加,巷道的预应力损伤程度和区域以及初始位移逐渐变大。爆炸载荷单独作用下巷道几乎没有位移,且损伤较小。在爆炸载荷和预应力造成的损伤耦合作用下,巷道位移和损伤随地应力增大而增大。地应力与爆炸载荷耦合作用下,爆炸产生的应力在巷道中的传播被抑制,且随着地应力增加,抑制效果也更加明显。地应力存在两种作用:在爆炸载荷作用前,地应力的存在造成了巷道围岩的预应力损伤,降低了围岩强度,导致围岩在爆炸载荷作用下发生变形破坏;在瓦斯爆炸载荷作用于巷道围岩后,地应力对应力在围岩内的传播起到抑制作用。

高瓦斯矿井急倾斜综放面瓦斯涌出规律研究

针对四川广旺公司赵家坝煤矿1944综采工作面上隅角瓦斯超限的问题,采用单元法在现场测量工作面瓦斯涌出量和采空区漏风量,研究了高瓦斯矿井急倾斜综放面瓦斯涌出规律以及U型上行通风工作面风流流动原理。结果表明,采面的瓦斯浓度从煤壁至中部再至采空区有先下降后上升的趋势,采空区的回风侧瓦斯浓度要比进风侧高,靠近回风侧的采面上部(上隅角附近)是瓦斯浓度容易超限的区域;采面上、下隅角部分的漏风量最大,在上、下隅角采取堵漏措施可以有效防止采空区瓦斯涌出至工作面。

煤层高压气水混压技术及其有效影响半径测试研究

针对现在煤层纳米级孔隙内瓦斯抽采率低的难题,研发了煤层高压气水混压技术,给出了其高压气水混压的技术原理,即依靠高吸附能力的水分置换出甲烷,再注入高压空气驱替孔裂隙中的水分解除“水锁”效应。在川煤绿水洞煤矿开展了初步现场试验,施工3组气水混注考察钻孔,取样分析了采取技术措施后的残余瓦斯含量在1.76~6.75 m3/t之间(除去一个异常点的含量为10.51 m3/t),通过与原始瓦斯含量(9.02 m3/t)对比,最终确定其气水混注有效影响半径最大可以达到48 m。

复合储层层间窜流对瓦斯抽采的影响机制研究

为了考察复合储层中围岩特性对穿层钻孔瓦斯抽采的影响,分析了煤层和岩层内瓦斯的渗流规律,基于建立的复合储层和单一储层瓦斯抽采流固耦合模型,模拟研究了不同倾角的穿层钻孔对复合储层和单一储层的瓦斯抽采效果,以及多钻孔耦合下的穿层钻孔瓦斯抽采效果。结果表明:相同钻孔抽采不同储层的煤层瓦斯时,复合储层比单一储层抽采瓦斯的抽采影响半径和有效半径大,抽采效果更好;不同倾角的钻孔对复合储层的瓦斯抽采影响不同,瓦斯抽采影响范围随夹角的增大呈降低趋势,层间窜流的影响也随之呈减弱趋势;在多钻孔耦合抽采下,复合储层中下部煤层的瓦斯压力明显低于单一储层中相同位置的瓦斯压力。

近水平特厚煤层放顶煤开采覆岩移动规律试验研究

近水平特厚煤层开采的覆岩移动变形大,对地层移动和瓦斯运移影响较大。利用相似模拟试验方法,研究了在开采过程中覆岩的移动规律。通过建立150∶1的模型,模拟了塔山煤矿3-5#煤层开采过程中上覆岩层垮落和裂隙的发育规律。结果表明,3-5#煤层顶板的最大下沉量达14.3 m,煤层开采后的遗留空间较大,垮落的块状结构无法填充整个采空区,覆岩最大下沉速度达5.2 m/d,下沉速度经历了“缓慢—逐渐增大到峰值—快速减少—趋于稳定”的过程,且最大裂隙发育高度达160 m左右,远大于薄煤层开采,相关研究结果可以为具有类似条件的特厚煤层开采提供借鉴。

Study on "fracturing-sealing" integration technology based on high-energy gas fracturing in single seam with high gas and low air permeability

To improve the gas extraction efficiency of single seam with high gas and low air permeability,we developed the"fracturing-sealing"integration technology,and carried out the engineering experiment in the3305 Tunliu mine.In the experiment,coal seams can achieve the aim of antireflection effect through the following process:First,project main cracks with the high energy pulse jet.Second,break the coal body by delaying the propellant blasting.Next,destroy the dense structure of the hard coal body,and form loose slit rings around the holes.Finally,seal the boreholes with the"strong-weak-strong"pressurized sealing technology.The results are as follows:The average concentration of gas extraction increases from8.3%to 39.5%.The average discharge of gas extraction increases from 0.02 to 0.10 m^3/min.The tunneling speeds up from 49.5 to 130 m/month.And the permeability of coal seams improves nearly tenfold.Under the same conditions,the technology is much more efficient in depressurization and antireflection than common methods.In other words,it will provide a more effective way for the gas extraction of single seam with high gas and low air permeability.

Effect of high-voltage thermal breakdown on pore characteristics of coal

High-voltage thermal breakdown has great potential application in permeability enhancement of coal seam. The characteristics of the breakdown channel, coal element, porosity and microscopic coal petrography of coal under high-voltage electric load were experimentally studied. The coal interior left apparent tracks due to electric current burning with high temperature. The percentage of C, O, Al, Fe, and Si had slightly decreased, while the content of element N increased obviously. Low-pressure nitrogen gas adsorption(LP-N_2GA) and mercury intrusion analysis showed that coal porosity increased. The increases of micropores and mesopores are beneficial to promotion of the ability of gas storage, and the increase of macropores could enhance the gas seepage and migration. The results of scanning electron microscope(SEM) show that there are many exogenous fractures in coal, which is also beneficial to gas seepage and migration. The results lay a theoretical foundation for application of high-voltage thermal breakdown in coal mines.

A numerical simulation of the influence initial temperature has on the propagation characteristics of, and safe distance from, a gas explosion

A model roadway with a cross-sectional area of 80 mm 80 mm and a length of 100 m was used to estimate the overpressure, the temperature, the density, and the combustion rate during an explosion. Auto-ReaGas software was used for the calculations and the initial temperatures were 248, 268, 308, or 328 K. The methaneair mixture had a fuel concentration of 9.5% and the tunnel had a filling ratio of 10%. The results show that the safe distance necessary to avoid harm from the shock wave increases with increasing initial temperature. The distance where the peak overpressure begins to rise, and where the maximum value occurs, increases as the initial temperature increases. These are almost linear functions of the initial temperature. At locations before shock wave attenuation has occurred increasing the initial temperature linearly increases the maximum temperature at each point following along the tunnel. At the same time, the peak overpressure, the maximum density, and the maximum combustion rate decrease linearly. How-ever, after the shock wave has attenuated the attenuation extent of the peak overpressure decreases with an increase in initial temperature. The influence of the initial temperature on the explosion propagation depends on the combined effects of inhibiting and enhancing factors. The research results can provide a theoretical guidance for gas explosion disaster relief and treatment in underground coal mines.

Effect of roadway turnings on gas explosion propagation characteristics in coal mines

In order to reveal the effect of turnings on explosion propagation, experiments were performed in three different pipes （single bend, U-shaped pipe and Z-shaped pipe）. Flame and pressure transducers were used to track the velocity at the explosion front. When the pipes were filled with methane, the explosion strength was significantly enhanced due to the turbulence induced by increasing the number of turnings, while the flame speed （Sf） and peak overpressure （ΔPmax） increased dramatically. In addition, the strength of the explosion increased in violence as a function of the number of turnings. However, when the bend was without methane, the turnings weakened the strength of the explosion compared with the ordinary pipe, shown by the decrease in the values of ΔPmax and Sf. In addition, the propagation characteristics in a U-shaped pipe were similar to those in a Z-shaped pipe and the values of APmax and Sf were also close. The results show that the explosion propagation characteristics largely depend on gas distribution in the pipes and the number of turnings. The different directions of the turnings had no effect.

平煤十二矿高瓦斯突出煤的孔隙及显微结构特征

煤作为一种多孔介质材料,其物理特性如孔隙度、渗透率会受到微观孔隙结构的影响,从而影响煤层内瓦斯的吸附、扩散和渗流。因此在煤层开采和瓦斯抽采工作开始前,需对该煤层煤样的微观孔隙结构进行测定。本文选取平煤十二矿的煤样,通过工业分析和显微煤岩组分分析,测得平煤十二矿煤样的煤种为焦煤,为中高变质程度煤种。利用扫描电镜分析煤样微观结构,发现煤样表面结构粗糙,气孔大量发育,煤中的内生和构造裂隙发育不好。通过压汞法研究,发现孔隙结构大部分集中于大孔且煤样在大孔部分孔喉粗大,连通性好,煤样储层大孔发育,但是中孔不发育。通过氮吸附法,测得该煤样孔径分布过渡孔占总孔体积的61.42%,中孔为38.58%;PM-12煤样比表面积为3.250e-2㎡/g,未检测出煤样微孔,过渡孔占总比表面积的77.66%,中孔占22.34%。

ON GAUGE COVARIANT FORMULATION OF STRING FIELD THEORIES II

The rules of truncation for getting a gauge invariant action from a gauge-fixed action are put forward and completed.It is shown that the presently well-known gauge invariant action(ψ|Q_(B)|ψ)can also be obtained by means of truncaton.The confusion of considering this action as a gauge-fixed action is clarified.

THE ELECTRIC MONOPOLE IN KALUZA-KLEIN THEORY

We have completely inteqrated out the field equations to obtain all sephericeally symmetric electric monopole solutions in the five dimenisional Kaluza-Klein theory.A epecifie solution ie given and itg relevance to the elassical theory of electron is diecused.

COMPACTIFICATION OF STRING THEORY ON COSET SPACE

String theory is constructed on group manifold which is locally neither a Minkovski nor a Euclidean space.It is shown that Lorentz algebra is satisfied and ghost states can all be eliminated.The string theory constructed is just like a string theory in four dimensions.

Explosive characteristics of nanometer and micrometer aluminum-powder

The explosive characteristics of aluminum powder have great significance in preventing and controlling aluminum-dust explosion accidents, especially the nano-aluminum powder. The explosion characteristics of 100 nm and 75 μm aluminum powders were investigated by using a 20 L spherical explosion cavity and a horizontal pipe whose cross-section area is 80 mm × 80 mm and length is 8 m. The results show that the maximum explosion pressure and its rising rate of 100 nm aluminum powder gradually increase with increasing concentration of aluminum-powder at the beginning. When aluminum-powder concentration is I kg/m3, the maximum explosion pressure reaches its maximum, and then gradually decreases. While when the concentration is 1.25 kg/m3, the maximum rate of pressure rise obtains its maximum, and then decreases. After 100 nm aluminum powder is exploded in pipes, the peak overpressure of blast wave first decreases and then increases to the maximum at a distance of 298 cm from the ignition source, and then gradually decreases. The most violent concentration is about 0.4 kg/m3 which is lower than 0.8 kg/m3 of 75 μm aluminum powder, so 100 nm aluminum powders are more easily exploded. The change laws of maximum explosion pressure, maximum rate of pressure rise and blast-wave peak overpressure of 100 nm aluminum powders with concentration are similar to those of 75 ktm aluminum powders, but these values are much higher than 75 Bm aluminum powders under the same concentration, so the aluminum-powders explosion of 100 nm will produce more harms. In the process of production, storage and transportation of aluminum powder, some relevant preventive measures can be taken to reduce the loss caused by aluminum-dust explosion according to nano-aluminum dust.

高瓦斯煤层气水混压强化瓦斯抽采工程实践研究

针对单一化增透瓦斯抽采的局限性问题,为提高瓦斯抽采效率,在某高瓦斯煤矿21603底抽巷进行气水交变驱替试验,基于实施区域条件,进行气水混压钻孔设计,测试注水注气后的残余瓦斯压力和含量,与实验区域原始瓦斯相应数据进行比较,同时监测瓦斯抽采流量和体积分数随时间的变化规律。结果表明,在瓦斯抽采工程中,气水交变驱替技术可充分降低煤层残余瓦斯含量和压力,瓦斯抽采混合量大幅增加,与临近运顺掘进工作面单一水压增透瓦斯抽采纯量进行比较,瓦斯抽采纯量明显提高。气水混压强化瓦斯抽采工程可提高施工质量与效率,确保施工安全,最终达到节约成本、缩短工期的目的。