恒稳推进的煤与瓦斯突出

本文建立理想的一维运动模型,对煤与瓦斯突出的机理进行了探讨,指出煤的破碎起动与瓦斯渗流的耦合是煤与瓦斯突出的内在因素,大型突出相应于恒稳推进的情况,通过分析给出了讨论煤与瓦斯突出的重要的无量纲参数以及突出判据的近似形式。     

瓦斯渗流场作用下煤层抽放钻孔弹塑性解

为研究瓦斯渗流场作用下的煤层抽放钻孔周围应力分布情况,假定钻孔周围煤体中瓦斯的流动为稳定径向流动状态,建立了渗流力学模型,给出了瓦斯径向稳定渗流方程;在考虑瓦斯渗流场作用下,推导了钻孔周围煤体的微元体力学平衡方程,并引入应力调整系数,求解出其弹性应力解析解;再应用Mohr-Coulomb屈服准则,求解出钻孔周围煤体的塑性应力和塑性半径的解析表达式。通过实例分析表明:钻孔内的抽放负压对钻孔周围煤体应力、塑性区的半径等参数影响较小;在一定的抽放负压(15k Pa)下,随着煤层原始瓦斯压力的增大,钻孔周围煤体的塑性区半径随之增大,距钻孔足够远处的弹性区煤体的应力也随之增大,这比不考虑瓦斯渗流场作用时的经典弹塑性解更加符合实际情况。     

峰后岩石非Darcy渗流的分岔行为研究

煤矿采动围岩大多处于峰后应力状态或破碎状态，其渗流一般不符合Darcy定律，为非Darcy渗流系统．峰后岩石非Darcy渗流系统的失稳和分岔是煤矿突水和煤与瓦斯突出动力灾害发生的根源．文中用谱截断方法建立了Ahmed-Sunada型非Darcy渗流系统的降阶动力学方程，再由变量代换得到以无量纲变量表示的平衡态附近的演化方程，分析了系统的分岔条件，给出了系统的各种吸引子图案，并结合采矿工程实际，用非线性数学的观点揭示了煤矿突水和煤与瓦斯突出的机理．研究表明：当非Darcy渗流系统渗流特性和边界压力的初始值满足一定条件时，系统由平衡转向不稳定，即存在跨临界Hopf分岔和切分岔，并且，系统的动力学响应不随渗透特性连续变化，即该系统存在突变性．     

煤在瓦斯一维渗流作用下的初次破坏

作者观察了煤在瓦斯一维渗流作用下的初次破坏,发现破坏煤体呈球冠状;临界破坏瓦斯超压取决于卸载条件,煤型的强度、半径和长度,以及煤型所受的侧压,但与瓦斯吸附特性无关。对实验例进行了数值分析,结果表明煤体的破坏属于拉伸破坏;卸载速率的增高,侧向围压的减小与煤型几何半径的增大将使得煤体在瓦斯渗流作用下更易于破坏。     

含水率对煤与瓦斯突出能量转化影响试验

为获得煤层注水对煤与瓦斯突出弱化的影响规律,以阜新孙家湾煤矿埋深1100m突出煤层为研究对象,建立了煤与瓦斯突出能量转化模型,并利用自主研发的煤与瓦斯突出模拟试验系统,进行了含水率对煤与瓦斯突出试验影响研究,分析了煤样含水率与临界孔隙压力、突出强度、能量转化率之间的关系。试验结果表明:孔隙压力是煤与瓦斯突出的主要动力源,煤样含水率与临界孔隙压力间呈指数关系递增。煤样含水率由0%增加到3%、6%时,相对突出强度分别降低了5.67%、1.2%,随煤样含水率增加,相对突出强度与绝对突出强度将逐渐降低。瓦斯内能是影响煤体突出能量大小的关键因素,与突出孕育和突出激发过程均密切相关。随含水率增加,突出孕育能量和突出激发能量均线性增加,但突出能量转化率线性减小,不易发生煤与瓦斯突出。     

低渗透多孔介质渗流动边界模型的解析与数值解

考虑启动压力梯度的低渗透多孔介质非达西渗流模型属于强非线性动边界问题, 分别利用相似变量变换方法和基于空间坐标变换的有限差分方法, 对内边界变压力情况下、考虑启动压力梯度的一维低渗透多孔介质非达西渗流动边界模型进行了精确解析与数值求解研究. 研究结果表明:该动边界模型存在唯一的精确解析解, 且所求得的精确解析解可严格验证数值解的正确性;且当启动压力梯度值趋于零时, 非达西渗流动边界模型的精确解析解将退化为达西渗流情况下的精确解析解. 由求解结果作出的非零无因次启动压力梯度下的地层压力分布曲线表现出紧支性特点, 其与达西渗流模型的有显著不同. 因此, 研究低渗透多孔介质中非稳态渗流问题时, 应该考虑动边界的影响. 研究内容完善了低渗透多孔介质的非达西渗流力学理论, 为低渗透油气藏开发的试井解释与油藏数值模拟技术提供了理论基础.      

高瓦斯煤层冲击地压发生条件与影响因素

针对高瓦斯煤层冲击地压问题,用解析方法得到冲击地压发生条件,分析了主要影响因素对满足冲击地压发生条件的临界塑性区半径和临界应力的影响规律.结合五龙矿开采实际情况对影响高瓦斯煤层冲击地压的煤的模量比、煤层瓦斯孔隙压力、支护应力和内摩擦角4个因素做了对比分析.研究发现:高瓦斯煤层在巷道掘进面附近由于存在开挖面空间效应,掘进面前方尚未开挖的煤体对巷道变形起到了限制作用,减少了冲击地压的发生,随着掘进面向前推进,后方一定距离范围内的巷道支护应力增大.随着瓦斯解吸渗流的进行,巷道壁处孔隙压力降低,巷道冲击地压危险性明显提高,此时提高支护应力,冲击危险性有所降低.高瓦斯煤层巷道发生冲击地压的临界塑性区半径和临界应力随模量比、瓦斯孔隙压力的增大而快速减小,随支护应力的增大而增大,临界塑性区半径随内摩擦角的增大而增大,临界应力与内摩擦角不是单调函数关系,存在一个极小值点,当内摩擦角小于此极小值时,临界应力随内摩擦角增大而减小;当内摩擦角大于此极小值时,临界应力随内摩擦角增大而增大.     

煤矿瓦斯突出的多因素综合预测

煤与瓦斯突出的预测预报是煤矿瓦斯灾害研究的一个主要方面.多因素综合预测理论借助了当前最新的模糊数学理论,对瓦斯矿井的工作面和区域进行突出危险性预测,从而为预测和防治煤与瓦斯突出提供一条新的途径.根据本文的计算结果和实际情况的对比,多因素综合评价方法在煤矿瓦斯突出预测方面较为准确,是可行的.     

非达西渗流拟启动压力梯度推算

岩体启动压力梯度的大小是石油开采,工程防渗处理等方面需要考虑的影响因素。非线性渗流现象已被广泛所认同,低渗透性岩渗流存在启动压力梯度,它基本代表了流体产生渗流时的压力梯度大小。试验对试样进水端水压进行长期稳定控制,出水端采用精确测定流出水体积变化量的方法进行流量测定; 当渗出端水体积的变化量与时间呈直线关系时,即认为该时段渗透特征符合达西定律。通过对具有不同渗透性的软弱岩系统的试验测试,根据实测渗透系数与压力梯度的正相关关系,提出了拟启动压力梯度推算的"三次平均法",即:首先统一调整实测渗透系数值,然后确定绝对渗透系数值,再根据该值确定V0值, 3次取平均推算拟启动压力梯度的方法。分析表明:拟启动压力梯度随围压升高而增大,随岩石的绝对渗透系数降低而增大; 在渗透压差增大过程测得的拟启动压力梯度大于降低过程的拟启动压力梯度,这些都与理论分析结果相吻合。实例说明拟启动压力梯度推算"三次平均法"较为合理,易于推广使用。这为通过室内试验确定工程岩体启动渗流压力梯度的大小,提出了一种新的思路。     

含气多孔介质卸压层裂的间隔特征——突出的前兆

含气多孔介质在卸压下的拉伸破坏有两种模式－层裂和突出，达到或超过临界破坏条件，引发骨架层裂破坏，达到或超过更强一些的临界突出条件，则引发突出，从采煤实践中逐次掘进的长过程看，层裂是已达破坏条件而未到突出条件的情况，进一步发展可能引发突出。实验表明层裂显微镜规律的间隔特征，因而与层裂相关的瓦斯浓度变化和地音信息可以认作是突出的前兆，如果在内部形成破坏区，渗流场与应力场的耦合有可以导致延时突出，石门自     

One-dimensional flow model for coal-gas outbursts and initiation criterion

This paper discribes a one-dimensional flow model to explain the basic mechanism of coal-gas outbursts. A break-start criterion of coal, as the elementary outburst criterion, is given approximately. In this ideal model, the tectonic pressure before excavation, as a load on coal body, affects the break-start and then the flow field. The flow field is decoupled with the stress field, so that the gas seepage through unbroken coal body, break-start and consequent two-phase flow, and pure gas flow can be analysed independently of the stress field. The tunnelling, an external disturbance that makes the seepage intensify relatively, is an essential factor for initiating outburst. Under steady tunnelling, seepage ought to tend to be steadily progressive. From its asymptotic solution initiation criterion is obtained. This is described by three conditions, possibility condition —tectonic pressure condition, incubation condition—tunnelling or gas condition and triggering condition —seepage velocity condition. The project supported by the National Natural Science Foundation of China     

Damage Evolution and Post-peak Gas Permeability of Raw Coal Under Loading and Unloading Conditions

Coalbed methane, a naturally occurring gas in coal, is regarded as a relatively clean-burning and eco-friendly resource. During mining, coalbed methane may be leaked to the environment, leading to potential coal mine catastrophes such as coal and gas outbursts, and gas explosions. In the interest of mine stability, and to enhance resource recovery and utilisation, it is fundamentally important to understand the permeability characteristics of coal, in particular its post-peak permeability behaviour. In this paper, an in-house developed tri-axial apparatus with the ability to investigate coupled thermal–hydrological–mechanical behaviour under servo-controlled seepage has been used to carry out a series of gas permeation experiments in coal samples. The coal samples were subjected to tri-axial tests, including the simulation of coal extraction by unloading the confining pressure applied on the test specimens. The deformation and permeability characteristics of raw coal during these tests were recorded. The volume changes of the coal samples during the tests were observed to occur in three stages: Stage 1: contraction, Stage 2: little or no volume change, and Stage 3: dilation. Corresponding to the volume changes, the gas seepage can also be divided into three stages: seepage decrease, steady seepage, and accelerated seepage. Based on the observed behaviour of coal samples during the tri-axial permeation tests, an analytical model to simulate damage evolution and its effect on the permeability of coal containing gas is proposed in this paper. It may be used to study the evolution of permeability with stress changes, and to provide insights into coal and gas outbursts in practice.     

煤层气在非饱和水流阶段的非定常渗流摄动解

煤层甲烷由煤层的割理裂隙系统流入生产井一般经历：单相水流、非饱和流和气、水两相饱和流三个阶段，在非饱和流阶段，储层压力降至临界解吸压力之后，储存在煤基质中的吸附气体少量被解吸出来形成互不连续的气泡并阻止水的流动，含气量尚未达到饱和程度。同时煤层甲烷运移包含渗流场、变形场和应力场的动态耦合过程。本文考虑渗流过程中水-气两相不溶混流体与固体耦合作用，建立了非饱和水流阶段非定常渗流问题的流固耦合数学模型，对该强非线性一维数学模型采用摄动法和积分变换法进行解析求解，并讨论了其压力动态特性，分析了压力随饱和度S及时间t变化的规律和气相及耦合作用的影响，这些研究对煤层气、石油和天然气的开采等地下工程领域具有一定的指导意义。     

多孔介质应力对孔隙压力影响的研究

通过大量的现场测试发现 ,含瓦斯煤岩是一个复杂的系统 ,煤体应力的变化是引起其他一系列变化的主导因素。随煤体应力的变化 ,孔隙压力呈指数形式变化 ;介质的渗透性受孔隙压力梯度的控制。     

Multi-scale Fractured Coal Gas–Solid Coupling Model and Its Applications in Engineering Projects

With coal mining entering the geological environment of “high stress, rich gas, strong adsorption and low permeability,” the difficulty of joint coal and gas extraction clearly augments, the risk of solid–gas coupling dynamic disasters greatly increases, and the underlying mechanisms become more complex. In this paper, based on the characteristics of coal’s multi-scale structure and spatiotemporal variation, the multi-scale fractured coal gas–solid coupling model (MSFM) was built. In this model, the interaction between coal matrix and its fractures and the mechanical characteristics of gas-bearing coal were considered, as well as their coupling relationship. By MATLAB software, the stress–damage–seepage numerical computation programs were developed, which were applied into Comsol Multiphysics to simulate gas flow caused by coal mining. The simulation results showed the spatial variability of coal elastic modulus and cross-flow behaviors of coal seam gas, which were superior to the results of traditional gas–solid coupling model. And the numerical results obtained from MSFM were closer to the measured results in field, while the computation results of traditional model were slightly higher than the measured results. Furthermore, the MSFM in a large scale was verified by field engineering project.     

Coal Permeability Evolution and Gas Migration Under Non-equilibrium State

Laboratory test of coal permeability is generally conducted under the condition of gas adsorption equilibrium, and the results contribute to an understanding of gas migration in the original coal seams. However, gas flow under the state of non-equilibrium, accompanied by gas adsorption and desorption, is more common in coalbed methane (CBM) recovery and \(\hbox {CO}_{2}\) geological sequestration sites. Therefore, research on gas migration under the non-equilibrium state has a greater significance with regard to CBM recovery and \(\hbox {CO}_{2}\) geological sequestration. However, most permeability models, in which only one gas pressure has been considered, cannot be used to study gas flow under the non-equilibrium state. In this study, a new mathematical model, which includes both fracture gas pressure and matrix gas pressure, and couples the gas flow with the coal deformation, has been developed and verified. With the developed model, the spatial and temporal evolution of gas flow field during gas adsorption and desorption phases has been explored. The results show that the gas pressures present nonlinear distributions in the coal core, and the matrix gas pressure is generally lower than the fracture gas pressure during adsorption, but higher than the fracture gas pressure during desorption. For gas flow during adsorption, the main factor controlling permeability varies at different points. At the initial time, the permeability is dominated by the effective stress, and at the later time, the permeability in the part close to the gas inlet is mainly controlled by the matrix swelling, whereas that in the part close to the gas outlet is still dominated by the effective stress. For gas flow during desorption, from the gas inlet to the gas outlet, the permeability deceases at the initial time, and when the time is greater than 10,000 s, it shows a decreasing and then an increasing trend. The reason is that at the initial time, the permeability is dominated by the increased effective stress caused by the sharp decrease of the fracture gas pressure. Later, desorption of the adsorbed gas results in matrix shrinkage, which further leads to an increase of the permeability.     

Mathematical Model of Coalbed Gas Flow with Klinkenberg Effects in Multi-Physical Fields and its Analytic Solution

The deep-mining coal seam impacted by high in situ stress, where Klinkenberg effects for gas flow were very obvious due to low gas permeability, could be regarded as a porous and tight gas-bearing media. Moreover, the Klinkenberg effects had a significant effect on gas flow behavior of deep-mining coal seam. Based on the gas flow properties of deep-mining coal seams affected by in situ stress field, geothermal temperature field and geo-electric field, a new mathematical model of coalbed gas flow, which reflected the impact of Klinkenberg effects on coalbed gas flow properties in multi-physical fields, was developed by establishing the flow equation, state equation, and continuity equation and content equation of coalbed gas. The analytic solution was derived for the model of one-dimensional steady coalbed gas flow with Klinkenberg effects affected by in situ stress field and geothermal temperature field, and a sensitivity analysis of its physical parameters was carried out by comparing available analytic solutions and the measured values. The results show that the analytic solutions of this model of coalbed gas flow with Klinkenberg effects are closer to the measured values compared to those without Klinkenberg effects, and this model can reflect more accurately gas flow of deep-mining coal seams. Moreover, the analytic solution of this model is more sensitive to the change of Klinkenberg factor b and temperature grad G than depth h.