晋城无烟煤煤中CH4和CO2运移规律研究

基于三轴应力条件下,煤岩有效应力、吸附膨胀量和渗透率的一体测试,研究了晋城无烟煤吸附甲烷和二氧化碳后,渗透性随有效应力改变和煤岩吸附膨胀效应的变化规律.认为煤岩吸附膨胀量和孔隙压力的关系可用兰氏方程描述;煤岩渗透性同有效应力、吸附膨胀量均呈负指数函数关系,同时结果表明:甲烷和二氧化碳在晋城无烟煤中的扩散方式不同,煤岩对甲烷的吸附膨胀符合单孔气体扩散模型,而对二氧化碳的吸附膨胀符合双孔气体扩散模型,且甲烷的吸附膨胀速率小于二氧化碳的吸附膨胀速率;煤岩饱和吸附后,各孔隙压力条件下的初始渗透率与孔隙压力呈幂函数关系减小.针对晋城无烟煤,同等条件下煤岩吸附甲烷后的渗透率为吸附二氧化碳后渗透率的1.14～1.51倍,大部分在1.30倍左右.     

承压颗粒煤逐级加载下渗透特性实验研究

为了识别覆岩应力及颗粒粒径对破碎煤体渗透的影响效应,通过承压破碎遗煤的渗流实验,得到了应力逐级加载过程中渗透率与加载应力、粒径、渗流梯度间的关系.结果表明:1)承压破碎颗粒煤的应力-应变曲线具有明显的阶段特征,在0~6 MPa区间快速压实,在6~12 MPa区间缓慢压实,12 MPa后压实效应微弱.2)测试过程中煤样的空隙率、渗透率随应力增大逐渐降低;而偏达西因子始终为负值,其绝对值随应力增加而增加.3)在相同轴向应力加载下,空隙率、渗透率随颗粒粒径的增加而降低,而其衰减系数随颗粒粒径的增加而增加.4)在应力加载过程中煤样内部物理结构发生变化,造成煤样的粒级构成变化,致使破碎分形维数增加,颗粒煤出现再次破碎,进而影响其渗透行为.5)通过承压破碎煤体渗流实验,说明采空区应力的逐渐恢复,将造成遗煤堆积区的空隙率、渗透率不断下降;通过降低煤体的破碎度、减少小颗粒比重有助于降低空隙率及渗透率,进而有利于煤自燃防治.     

不同煤体电性参数影响因素实验研究

为了研究温度、水分和不同气体解吸过程与不同煤体电性参数之间的作用关系,以大淑村矿、余吾煤业和寺河煤矿煤样为研究对象,通过建立煤体电性参数实时测试系统,分析了温度、水分和不同气体解吸等影响因素对不同煤体电性参数的影响,进一步解释了不同影响因素对煤体电性参数变化的作用机理.结果表明:温度的升高改变了煤体内部水分和矿物质成分的含量,影响了电子的赋存状态,随温度的升高,不同煤体电阻率缓慢减小,而相对介电常数则缓慢增大;未饱和含水状态下煤体的电性参数变化规律与煤体本身性质有密切的关联,而饱和状态下煤体电阻率表现为水分的电阻率特征,介电常数则表现为水分的极性特征;不同气体的吸附解吸过程改变了煤体内部孔隙、裂隙等晶体缺陷结构的压缩闭合状态,同时由于气体解吸过程放热改变了内部电子的赋存环境、数目及状态,从而改变了不同煤体的电性参数变化规律,并呈现出明显的差异性.     

煤样瓦斯渗透率的实验研究

煤和瓦斯突出是威胁煤矿井下安全生产的一个严重问题,而突出的发生将取决于瓦斯压力、煤层渗透率以及煤体强度等参数。因此,煤层渗透率对于煤和瓦斯突出以及煤层瓦斯抽放都具有重要意义.本文研究含瓦斯煤体在围压力不变的前提下,孔隙压力和渗透率以及孔隙压力和煤样变形间的关系;同时还研究了在孔隙压力一定的条件下,渗透率和围压力以及煤样变形间的关系;得出了在围压力不变的前提下,孔隙压力和渗透率以及煤样变形值间的关系基本上服从指数方程:K=u_1e~((?)v_1~p),S=u_2e~(v_2~p);在孔隙压力不变条件下,加载时,煤体的渗透率与载荷间的关系可用负指数方程表示:K=ae~((?)bσ);卸载时,可用幂函数方程表示:K=K_oσ~(-c)。     

应力与温度综合作用的煤岩渗透机理

为评估深部煤岩的瓦斯抽采特性,探究不同条件下煤岩渗透率演化规律,利用含瓦斯煤热-流-固耦合三轴伺服渗流装置,开展不同平均有效应力和不同孔隙压力下温度升高的三轴渗流实验.基于分形理论表征温度引起的煤岩孔裂隙扩展和滑脱因子变化情况,进一步考虑压缩变形及滑脱效应对煤岩渗透率的影响,建立应力与温度综合作用的煤岩分形渗透率模型.结果表明:1)随温度升高煤岩整体具有压缩效应,渗流通道减小,渗透率先急剧下降后趋于平缓.2)在相同温度下煤岩渗透率随平均有效应力的增大逐渐减小,随孔隙压力增大先急剧减小后趋于平缓.煤岩裂隙压缩系数C_f随平均有效应力增大逐渐减小,随孔隙压力增大煤岩裂隙性系数具有相同的变化趋势.3)新建渗透率模型的计算值和实测值基本一致,其理论机理适用性及数据匹配度均优于Lu模型,该模型可以较好表征多因素影响下的煤岩渗透率演化规律.4)孔隙压力较低时,滑脱效应较为明显,且在孔隙压力升高初期考虑滑脱效应的煤岩渗透率曲线比不考虑滑脱效应的渗透率曲线更接近实验测量值.     

方向性原煤CH_4扩散实验及矢量计算模型

为了探讨温度、压力、扩散路径等因素对原煤CH4扩散特性的影响,采用规则块样结合气相色谱法进行不同温度、压力条件下方向性原煤CH4扩散实验。实验结果表明:原煤中CH4扩散速率较小,扩散系数大小处于10-8数量级上;原煤CH4扩散系数随围压、气压的增大,呈指数关系减小;随温度的升高,呈指数关系增大;扩散路径对扩散系数影响显著。分析表明:原煤CH4扩散实验不能用颗粒煤解吸实验简单替代;温度对气体分子扩散的控制是通过改变气体分子的均方根速度和平均自由行程,而围压、气压则受有效应力和煤粒收缩/膨胀变形两种因素的共同制约;方向性扩散系数是矢量,据此,推导建立了一种扩散系数矢量计算模型。     

可视化恒容气固耦合试验系统的研发与应用

为定量分析地应力、瓦斯压力、动力扰动等因素对预静载环境下含瓦斯煤物理力学性质的影响规律,获取不同加载路径和不同瓦斯压力下煤岩体物理力学参数,研制了可视化恒容气固耦合试验系统,配合伺服压力机,形成了以可视化恒容试验仪为主体的试验系统.通过实现含瓦斯煤耦合加载室容积恒定消除了气压改变对加载过程的干扰和误差,利用系统自带的环向位移测试装置和可视化窗口实现了对试件体应变增量、煤体裂隙发育与劣化规律等特征参数的全程可视化实时监测.开展了预加静载条件下不同强度型煤试件峰后快速卸气压扰动试验,模拟了现场煤层揭露致使瓦斯压力下降情况.试验结果表明:气体卸压时间在0.55s内完成,随着煤体强度的提高,游离瓦斯对煤岩试件的劣化程度随之降低;当峰值强度低于1 MPa时,游离气体将煤体完全剥离,强度在1.5~2.5 MPa时,卸压扰动对试件仅造成裂隙的进一步扩展;煤体扩容增量随强度的变化符合第一象限单调递减幂函数方程.仪器的研发为深入研究气固耦合条件下含瓦斯煤精确加载与可视化监测提供了新的测试手段和技术支撑.     

解吸-渗流作用下煤体变形及渗透规律试验研究

以铁新煤矿9#煤为原料制成的型煤为研究对象,利用自行研制的应力-解吸-渗流煤体变形试验装置,开展了不同围压和孔隙压力条件下的解吸-渗流试验.结果表明:在解吸-渗流过程中,围压恒定,孔隙压力以0.5 MPa/次的梯度降低时,煤体径向变形在1.0~1.5h内达到稳定;孔隙压力降低过程中,煤体径向应变增大,孔隙压力与径向应变呈二次函数关系,且解吸作用对煤体变形有一定的影响;在围压为5.0 MPa时,随着孔隙压力的减小渗透率先减小后增加,表明渗透率存在一个最小值,并且围压越大,最小渗透率对应的孔隙压力越大,渗透率存在最小值是由于解吸和有效围压的共同作用.     

反分析在粘土岩有效气体渗透性测量中的应用

为了研究粘土岩的气体渗透率特性,利用瞬间脉冲法测量原理,研究开发出低渗透率气体测量的三轴设备.并详细地介绍分析各种影响气体测量中的关键技术参数(气体压力、压力增量、温度和气体容器大小),结合反分析法准确地确定岩石的渗透率.借助该设备,粘土岩在不同应力水平条件的气体渗透率被跟踪测量.实验结果表明该设备可以准确测量低渗透岩石(10-21m2),该地质材料的气体渗透率随偏应力增加而减少,但即使材料已经处于损伤阶段,这种变化也非常微弱,因此气体渗透率的变化不能作为一个有效的损伤变量.     

煤基质收缩对渗透率影响的实验研究

在具有围限压力的情况下进行了煤岩体氦气和甲烷渗透率的平行实验；采用控制有效应力的方法,消除了因流体压力降低和气体解吸引起的渗透率变低问题；同时,利用克林伯格公式，校正了因气体分子沿壁面滑动而影响的渗透率，并定量地推导了煤基质收缩引起的渗透率变化情况。结果表明：渗透率增量随绝对渗透率的增加而增大，随流体压力的减少而呈对数形式减少；煤岩体氦气的绝对渗透率大于甲烷的克氏渗透率，在有效应力不变的情况下，流体压力愈小，滑脱效应愈明显；滑脱效应引起的渗透率增量越大;氦气滑脱效应大于甲烷。     

A method of determining the permeability coefficient of coal seam based on the permeability of loaded coal

This study developed the equipment for thermo-fluid–solid coupling of methane-containing coal, and investigated the seepage character of loaded coal under different working conditions. Regarding the effective pressure as a variable, the variation characteristics of the gas permeability of loaded methane-containing coal has been studied under the conditions of different confining pressures and pore pressures. The qualitative and quantitative relationship between effective stress and permeability of loaded methane-containing coal has been established, considering the adsorption of deformation, amount of pore gas compression and temperature variation. The results show that the permeability of coal samples decreases along with the increasing effective stress. Based on the Darcy law, the correlation equation between the effective stress and permeability coefficient of coal seam has been established by combining the permeability coefficient of loaded coal and effective stress. On the basis of experimental data, this equation is used for calculation, and the results are in accordance with the measured gas permeability coefficient of coal seam. In conclusion, this method can be accurate and convenient to determine the gas permeability coefficient of coal seam, and provide evidence for forecasting that of the deep coal seam.     

Simulation of microwave's heating effect on coal seam permeability enhancement

As hydraulic fracturing was forbidden in some countries due to possible negative environmental impacts and enhanced coalbed methane(ECBM) was restricted by in-situ conditions, microwave heating was proposed to enhance coalbed permeability. One of the mechanisms of improving coal permeability with microwave irradiation is that thermal expansion caused by microwave heating. To study the influence of microwave's heating effect of coal samples, the simulations were conducted using a coupled electromagnetic, thermal and mechanical model in this paper. The temperature, Von-Mises stress and strain distribution of coal sample are recorded every 10 s. The permeability distribution is also obtained based on the relationship between strain and permeability from articles. It was found that volume average temperature, stress, strain and permeability increase almost linearly with time. The average permeability increased from 1.65×10~(-16) m~2 to 3.63×10~(-16)m~2 under 2.45 GHz and 500W microwave radiation after 300s. The significant increase proved microwave to be effective in coal seam permeability enhancement.     

Resistivity response to the porosity and permeability of low rank coal

Laojunmiao coal samples from the eastern Junggar basin were studied to understand the relationship between coal resistivity and the physical parameters of coal reservoirs under high temperatures and pressures.Specifically,we analysed the relationship of coal resistivity to porosity and permeability via heating and pressurization experiments.The results indicated that coal resistivity decreases exponentially with increasing pressure.Increasing the temperature decreases the resistivity.The sensitivity of coal resistivity to the confining pressure is worse when the temperature is higher.The resistivity of dry coal samples was linearly related to φ~m.Increasing the temperature decreased the cementation exponent(m).Increasing the confining pressure exponentially decreases the porosity.Decreasing the pressure increases the resistivity and porosity for a constant temperature.Increasing the temperature yields a quadratic relationship between the resistivity and permeability for a constant confining pressure.Based on the Archie formula,we obtained the coupling relationship between coal resistivity and permeability for Laojunmiao coal samples at different temperatures and confining pressures.     

平顶山矿区煤层气赋存特征及开发潜力

平顶山矿区二1煤层富含煤层甲烷气体,其资源量估算达302亿m3以上．本文通过对控制煤层气赋存的二1煤层的传层几何形态、地质特征、煤质变化、特别是物性特征的研究,指出本区二1煤层渗透性较好,渗透率随着围限压力增加而降低,且与判及发育程度、构造应力变化有密切关系．而二1煤层中的煤层气含量与煤层理深有着密切关系,随着深度增加而增加．通过综合分析指出了开发潜力较好的区块．     

Mechanical property and permeability of raw coal containing methane under unloading confining pressure

Based on domestic-developed triaxial servo-controlled seepage equipment for thermal–hydrological–mechanical coupling of coal containing methane, an experimental study was carried out to investigate mechanical property and gas permeability of raw coal, under the situation of conventional triaxial compression and unloading confining pressure tests in different gas pressure conditions. Triaxial unloading confining pressure process was reducing confining pressure while increasing axial pressure. The research results show that, compared with the peak intensity of conventional triaxial loading, the ultimate strength of coal samples of triaxial unloading confining pressure was lower, deformation under loading was far less than unloading, dilation caused by unloading was more obvious than loading. The change trend of volumetric strain would embody change of gas permeability of coal, the permeability first reduced along with volumetric strain increase, and then raised with volume strain decrease, furthermore, the change trends of permeability of coal before and after destruction were different in the stage of decreasing volume strain due to the effect of gas pressure. When gas pressure was greater, the effective confining pressure was smaller, and the radial deformation produced by unloading was greater. When the unloading failed confining pressure difference was smaller, coal would be easier to get unstable failure.     

吸附气体对受载含瓦斯煤渗流特性影响的试验研究

利用自主研发的含瓦斯煤岩三轴压缩试验系统,进行了大量受载瓦斯煤的渗透特性室内试验,对比分析了CO2,CH4和N2的渗透率之间的异同.研究结果表明,在恒定瓦斯压力条件下,煤样渗透率随围压的增大而减小,均服从负指数函数变化规律;在恒定围压条件下,煤样渗透率随瓦斯压力的增加而减小,并且表现出幂函数变化规律;吸附性强弱不同的气体所表现出来的渗透性也不一样,气体吸附性越强,渗透性越弱;在轴向加载情况下,不同气体的渗透率都表现出先减小后增大的现象,并且具有一般的"V"字型变化规律.研究结果对深入认识煤层瓦斯运移规律具有一定的理论价值.     

Infrared measurement of temperature field in coal gas desorption

In order to reveal the temperature change in coal gas desorption process, the temperature variation in coal gas desorption process under different particle sizes is analyzed with infrared thermal imager. The infrared video signals obtained by the experiment are processed with SAT. Then the infrared radiation signals are processed by EMD with Hilbert–Huang and the infrared radiation noise is effectively removed. The research results show that the desorption process, with the change of the temperature, is an endothermic process. The coal absorbs heat when the gas is desorbed and the temperature drops. The coal body temperature drop range is obviously related to coal particle size. The smaller the particle size is, the bigger the temperature drop becomes. The temperature variation curves in the process of coal gas desorption under different particle sizes are fitted, and they comply with the exponential function. The research results lay the theoretical and experimental foundation for non-contact prediction on working face of coal and gas outburst with infrared thermal image technology.     

CO<Subscript>2</Subscript> permeability of fractured coal subject to confining pressures and elevated temperature: Experiments and modeling

The CO₂ permeability of fractured coal is of great significance to both coalbed gas extraction and CO₂ storage in coal seams, but the effects of high confining pressure, high injection pressure and elevated temperature on the CO₂ permeability of fractured coal with different fracture extents have not been investigated thoroughly. In this paper, the CO₂ permeability of fractured coals sampled from a Pingdingshan coal mine in China and artificially fractured to a certain extent is investigated through undrained triaxial tests. The CO₂ permeability is measured under the confining pressure with a range of 10–25 MPa, injection pressure with a range of 6–12 MPa and elevated temperature with a range of 25–70°C. A mechanistic model is then proposed to characterize the CO₂ permeability of the fractured coals. The effects of thermal expansion, temperature-induced reduction of adsorption capacity, and thermal micro-cracking on the CO₂ permeability are explored. The test results show that the CO₂ permeability of naturally fractured coal saliently increases with increasing injection pressure. The increase of confining pressure reduces the permeability of both naturally fractured coal and secondarily fractured coal. It is also observed that initial fracturing by external loads can enhance the permeability, but further fracturing reduces the permeability. The CO₂ permeability decreases with the elevation of temperature if the temperature is lower than 44°C, but the permeability increases with temperature once the temperature is beyond 44°C. The mechanistic model well describes these compaction mechanisms induced by confining pressure, injection pressure and the complex effects induced by elevated temperature.