煤层双重孔隙模型及采空区瓦斯运移的数值模拟研究

发布时间：2018-03-29 09:03

本文选题：瓦斯解吸　切入点：瓦斯抽采　出处：《中国矿业大学(北京)》2017年博士论文

【摘要】：煤矿开采的过程中,常伴随着各种事故的发生,瓦斯灾害、煤尘灾害、火灾、水灾和顶板事故仍然是我国煤矿的“五大灾害”,其中,以瓦斯灾害最为突出。我国多数矿井为高瓦斯矿井,抑制我国煤矿安全高效开采主控因素之一即为瓦斯问题。随着我国浅部煤炭资源的逐步枯竭,煤矿开采逐渐转为深部开采,瓦斯问题将愈发突出,深部煤层中瓦斯的含量、涌出量及涌出强度也必将大大增加,这也必将加剧瓦斯治理的难度和灾害发生的严重程度。瓦斯抽放是煤矿防治瓦斯事故的根本性措施,我国在采场即本煤层和采空区采用联合瓦斯抽放方法及抽放工艺方面,取得了一定的经验,在一定程度上缓解了采场瓦斯超限和局部瓦斯积聚问题,但由于未能搞清煤层钻孔及采空区瓦斯流场的变化规律,对于煤层钻孔及采空区的瓦斯运移的机理掌握不够,导致煤层及采空区瓦斯抽放效果普遍较差,抽放率低等。针对以上情况,本文以实验室实验、现场观测结果为基础,以理论分析和数值模拟为主导,通过理论分析煤层钻孔及采空区瓦斯涌出规律、流场动态变化规律及瓦斯运移机理,建立特定开采条件下采场瓦斯运移数学模型,编制开发煤层瓦斯运移数值解算程序,模拟煤层及采空区瓦斯运移规律,结合现场实际,提出煤层及采空区瓦斯抽采技术方案。首先分析了特定矿井瓦斯来源、涌出规律,实验室试验研究玉华煤矿煤样的瓦斯解吸规律,得到了玉华煤矿2108采煤工作面煤样的瓦斯吸附常数、煤体孔隙率、渗透率等重要参数,对煤层瓦斯赋存情况及煤体的各项物理性质有了更进一步的了解,同时得到了研究煤体钻孔瓦斯涌出相关参数的关键性数据。将瓦斯的解吸过程来模拟煤层和采空区遗煤的瓦斯放散过程,将采空区遗煤看作是大小不一煤粒松散堆积组合体,通过试验研究不同粒度范围、不同瓦斯解吸压力对一定质量的煤粒的瓦斯解吸规律,将试验结果应用到玉华煤业2108工作面采空区,得到该工作面采空区单位质量遗煤的瓦斯解吸特性参数,进而定性分析采空区瓦斯浓度分布规律。接着为探索玉华煤矿2108煤层瓦斯赋存情况及瓦斯涌出特征,进行了现场煤层原始瓦斯压力测定,并现场观测了钻孔自然排放时瓦斯流速、累积流量随观测时间的变化情况,为钻孔瓦斯涌出数值模拟提供基本参数,并为验证瓦斯涌出数值模型提供实测数据。在上述实验室实验及现场观测的基础上,结合煤体的双重孔隙特征,根据煤层瓦斯运移机理,提出了煤体双重孔隙瓦斯双渗流理论,认为钻孔瓦斯流动模型应包括基质瓦斯流动模型和裂隙瓦斯流动模型以及它们之间的耦合关联项,据此推导了煤体双重孔隙钻孔瓦斯双渗流数学模型,借助计算机语言自主开发了该模型的解算软件《钻孔瓦斯流动分析软件COMESS 2.0》,并借助该软件进行了瓦斯涌出过程的数值模拟,分别得到钻孔瓦斯涌出速度、累积瓦斯涌出量随时间的变化曲线,并与现场实测结果进行了对比,模拟得到的的钻孔瓦斯涌出速度、累积瓦斯流量整体上与实测结果是相符合的。接着使用自主开发的解算软件对不同抽放参数下的钻孔瓦斯涌出过程进行数值模拟,得到不同抽放参数对钻孔有效抽放半径的影响规律。在预抽时间一定时,抽放负压越大,钻孔有效抽放半径就越大,且随抽放负压的增大,其对有效抽放半径的影响逐渐减小。在钻孔抽放负压一定时,预抽时间越长,钻孔有效抽放半径就越大,且随预抽时间的推移,有效抽放半径的增大速率逐渐减小。在同一时刻,随抽放负压的提升,抽放纯量逐渐变大。随钻孔负压的提升,负压的变化对抽放纯量的影响程度逐渐减弱。单个钻孔的抽放纯量与钻孔直径呈线性关系,表明扩大钻孔直径会增加瓦斯抽放纯量并增大有效抽放半径。在现实条件允许的情况下,可以考虑尽量施工大直径钻孔。根据2#煤层2108工作面的现场情况及数值模拟结果,设计了该工作面的瓦斯抽放方案,确定抽放钻孔间距为6.5m,抽放负压为0.55MPa,预抽时间为270天。根据已确定的抽放参数,对该工作面的本煤层顺层抽放钻孔进行了参数布置。考虑采空区随工作面采动不断变化特点及遗煤瓦斯放散规律,进行采空区瓦斯运移规律的研究。基于流体基本定律,考虑采空区实际条件,建立了采空区二维瓦斯浓度场平衡方程,结合工作面采空区特点及边界条件,建立了采空区瓦斯浓度场求解数学模型。基于建立的采空区瓦斯运移数学模型,考虑开采过程中采空区的实际特点,确定采空区瓦斯浓度场计算模型范围,数值离散模型范围,基于有限体积法思想,离散瓦斯压力场和瓦斯浓度场,构建节点瓦斯压力和浓度计算线性方程组。线性方程组系数矩阵特点,将线性方程组系数矩阵进行压缩,利用高斯赛德尔法求解方程组;编制开发了采空区瓦斯运移模拟软件,并对特定开采条件下采空区瓦斯浓度场进行数值模拟。以玉华煤矿2108工作面为例,采用自主开发的采空区瓦斯数值解算软件,模拟玉华煤矿实际推进速度下采空区多物理场分布规律,包括气体压力场、风流速度、瓦斯放散速度及瓦斯浓度场。分析目前采空区瓦斯抽采的常用方法及其优缺点,基于理论、数值研究结果,结合玉华煤矿现场实际,提出了闭墙长插管的方式进行瓦斯抽采,并对抽采钻孔进行了参数布置。本文的创新性主要体现在以下三点:(1)在实验室实验研究以及现场测定相关参数的基础上,结合煤体的双重孔隙特征,根据煤层瓦斯运移机理,提出了煤体双重孔隙瓦斯双渗流理论,建立了煤体双重孔隙钻孔瓦斯双渗流数学模型;(2)自主开发了钻孔瓦斯流动数值模拟软件《钻孔瓦斯流动分析软件COMESS 2.0》。使用该软件对不同抽采参数下的钻孔涌出过程进行数值模拟,得到不同抽采参数对钻孔有效抽采半径的影响规律;(3)基于流体基本守恒定律,建立了采空区二维瓦斯浓度场平衡方程,考虑采空区实际边界条件,进而建立了采空区瓦斯浓度场数学模型。基于有限体积法思想,离散采空区瓦斯压力场和浓度场,构建节点瓦斯压力和浓度计算线性方程组;开发了采空区瓦斯运移数值模拟软件,并对特定开采条件下采空区多物理场进行了数值模拟。
[Abstract]:The process of coal mining, often accompanied by a variety of accidents, coal gas disaster, disaster, fire, flood and roof accidents of coal mine in our country is still the "five big disaster", among them, the gas disaster is most prominent. The majority of our mine for high gas coal mine, coal mine safety and high efficiency mining suppression of the main controlling factors for the gas problem. With the shallow coal resources in China's gradual depletion, coal mining gradually into deep mining, the gas problem will become increasingly prominent, the content of gas in deep coal seam, emission and emission intensity will greatly increase the difficulty and the severity of this disaster is bound to intensify the management of gas happen. Gas drainage is the fundamental measure to prevent gas accident in coal mine in our country, namely the stope coal seam and goaf by combined gas drainage method and drainage technology, has achieved some experience in a certain degree Ease of stope gas and local gas accumulation, but failed to find change of the coal seam drilling and goaf gas flow field, the mechanism of gas migration in coal seam and goaf area is not good, cause coal seam and goaf gas drainage effect is generally poor, low drainage rate for. The above, based on laboratory experiments, field observation results based on theoretical analysis and numerical simulation for leading coal seam drilling and goaf gas emission law through theoretical analysis, the mechanism of dynamic changes of flow field and gas migration, establish specific mining conditions of stope gas migration mathematical model, numerical solution preparation development of coalbed gas migration computer program, mining and rule of gas migration simulation of coal seam, combining with the actual, put forward coal seam and goaf gas drainage technology scheme. First analyzes the specific sources of mine gas gushing. By law, the gas desorption law of laboratory test of Yuhua Coal Mine coal sample, the gas adsorption constant work Yuhua Coal Mine 2108 coal mining face of coal, coal porosity, permeability and other important parameters, the physical properties of coal seam gas occurrence and coal are better understood, and gets the key data the relevant parameters of gas emission of coal drilling. The gas desorption process to simulate the process of gas emission of coal and coal in goaf, the coal goaf as a coal particle size of loose accumulation combination, through the test of different size range, the gas desorption law of different gas desorption pressure on certain the quality of the coal particles, the test results are applied to Yuhua Coal 2108 working face goaf, gas desorption characteristic parameters of the mining face goaf left coal quality unit, and qualitative analysis. The distribution of the concentration of gas in air. Then to explore the emission features of Yuhua Coal Mine 2108 coal seam gas occurrence and gas, the original coal gas pressure determination, and field observation of drilling natural gas emission velocity, the cumulative flow varying with observation time, provide the basic parameters for numerical simulation of borehole gas emission, and provide the test in order to verify the data of gas emission based on the numerical model. The observation in laboratory and field, combined with the dual pore characteristics of coal seam gas, according to the transport mechanism, put forward the coal gas double double pore flow theory that drilling gas flow model should include the coupling between flow matrix and crack gas gas flow model the model and the derived coal dual pore drilling gas double percolation mathematical model, with the help of computer language self development The model calculation software < borehole gas flow analysis software COMESS 2.0>, and the numerical simulation of gas emission process with the help of the software, get the speed of gas emission, emission of gas accumulation curve changes with time, and the results were compared with field test, simulation of borehole gas emission rate. The accumulation of gas flow on the whole and the measured results are consistent. Then using the self-developed software solution pumping borehole gas under different emission parameters is simulated. The influence law of different drainage parameters of drill hole effective drainage radius. In pre drainage time when the suction pressure is greater drilling, effective drainage radius is bigger, and with increase of suction pressure and its influence on the effective drainage radius decreases. In drilling drainage negative pressure, pre pumping time is longer, the effective pumping hole drilling Put the bigger the radius, and with the pre drainage time, effective pumping increase rate put radius decreases. At the same time, with the suction pressure increase, drainage volume becomes larger. With the pure negative pressure to enhance the impact of drilling, put on the pure volume change of negative pressure single gradually weakened. A drilling drainage borehole scalar and the linear relationship between the diameter of the hole diameter, indicating that the expansion will increase the amount of pure gas drainage and increase the effective drainage radius. In reality the conditions allow, can be considered as the construction of large diameter drilling. According to the simulation results and numerical field of 2108 working face in 2# coal seam, the design for gas the working surface drainage schemes, determine the drainage hole spacing is 6.5m, the suction pressure is 0.55MPa, pre drainage time was 270 days. According to the determined drainage parameters, the working surface of the seam drainage borehole parameters were considered gob layout. With mining changing characteristics and coal gas diffusion law, research on gas migration. Based on the basic laws of fluid, considering the actual goaf conditions, establish goaf gas concentration field of two-dimensional equilibrium equation, combined with the characteristics of goaf and the boundary conditions were established by gas concentration field of the mathematical model. The mathematical model of gas migration in goaf is established based on considering the actual characteristics of goaf in mining process, determine the goaf gas concentration field calculation model, numerical model, the finite volume method based on discrete gas pressure field and gas concentration field, build the node the gas pressure and the concentration calculation of linear equations. The coefficient matrix of the linear equations, the coefficient matrix of linear equation group is compressed by solving the equations of Gauss Seidel method; preparation of developed goaf tile Software simulation, migration, and the gas concentration of the specific mining conditions of stope was numerically simulated. In Yuhua Coal Mine 2108 working face as an example, the numerical goaf gas developed calculation software, the actual speed of simulation Yuhua Coal Mine Goaf under multi physical distribution, including gas pressure field. Airflow velocity, gas velocity and gas concentration field. Commonly used methods to analyze the gob gas drainage and its advantages and disadvantages, based on the theoretical and numerical results, combining with the actual Yuhua Coal Mine, put forward long closed wall intubation way for gas drainage, drainage and drilling parameters were arranged. The innovation of this paper is mainly reflected in the following three points: (1) based on Determination of related parameters were studied in laboratory experiments and field, combined with the dual pore characteristics of coal seam gas, according to the transport mechanism, put forward the coal body double Double porosity gas seepage theory, established coal dual pore drilling gas double percolation mathematical model; (2) developed a drilling gas flow numerical simulation software: drilling gas flow analysis software COMESS 2.0>. was simulated using the software of different pumping borehole parameters of the emission process, different extraction parameters on the effective drilling influence of mining pumping radius; (3) the basic conservation laws of fluid based on goaf was established two dimensional gas concentration field balance equation, considering the actual goaf boundary conditions, and then established the goaf gas concentration field mathematical model. The finite volume method based on discrete goaf gas pressure field and concentration field construction of nodes of gas pressure and concentration calculation of linear equations; the development of numerical simulation software of goaf gas migration, and the specific conditions of mining goaf under multi physics field in numerical simulation.

【学位授予单位】：中国矿业大学(北京)
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TD712

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