煤矿采动区煤层气井产能数值模拟及应用研究.pdf

煤炭科学研究总院 博士学位论文 煤矿采动区煤层气井煤矿采动区煤层气井 产能数值模拟产能数值模拟及及应用研究应用研究 作者姓名 赵继展 学科专业 矿产普查与勘探 导师姓名 张群 研究员 完成时间 二○一八年六月十五日 万方数据 万方数据 China Coal Research Institute A dissertation for doctors degree Study on Numerical Simulation and Application of Gob Coal Seam gas Well Productivity in Longwall Working Face Author’s Name Jizhan Zhao specialityMineral Resource Prospecting and Exploration Supervisor Prof. Qun Zhang Finished time June 15th, 2018 万方数据 万方数据 煤炭科学研究总院学位论文原创声明煤炭科学研究总院学位论文原创声明 本人郑重声明此处所提交的学位论文煤矿采动区煤层气井产能数值模拟 及应用研究 ，是本人在导师指导下，在煤炭科学研究总院攻读博士学位期间独 立进行研究工作所取得的成果。据本人所知，论文中除已注明部分外不包含他人 已发表或撰写过的研究成果。对本文的研究工作做出重要贡献的个人和集体，均 已在文中以明确方式注明。本声明的法律结果将完全由本人承担。 作者签名 日期 年 月 日 煤炭科学研究总院学位论文使用授权书煤炭科学研究总院学位论文使用授权书 煤矿采动区煤层气井产能数值模拟及应用研究 系本人在煤炭科学研究总 院攻读学位期间在导师指导下完成的学位论文。 本论文的研究成果归煤炭科学研 究总院所有，本论文的研究内容不得以其他单位的名义发表。本人完全了解煤炭 科学研究总院关于保存、使用学位论文的规定，同意学校保留并向有关部门送交 论文的复印件和电子版本，允许论文被查阅和借阅，同意学校将论文加入中国 优秀博硕士学位论文全文数据库和编入中国知识资源总库 。本人授权煤炭 科学研究总院，可以采用影印、缩印或其他复制手段保存论文，可以公布论文的 全部或部分内容。 本学位论文属于（请在以下相应方框内打“√“; 保密□,在 年解密后适用本授权书 不保密□ 作者签名 日期 年 月 日 导师签名 日期 年 月 日 万方数据 万方数据 摘 要 1 摘摘 要要 煤矿采动区煤层气井抽采是煤矿区煤层气抽采的特有方式， 是利用本煤层开 采产生的覆岩破断卸压促使上邻近煤层，尤其是碎软低渗煤层，强化增透、实现 煤层气地面高效抽采的重要途径， 也是煤矿井下防治回采工作面上隅角瓦斯超限 的有效措施。但是，多年来煤矿采动区煤层气井抽采产能数值模拟，一直是尚未 解决的世界性难题。论文依托“十二五”国家科技重大专项课题“煤矿区煤层气 抽采产能预测技术（2011ZX05040-003） ” ，以煤层群开采的安徽省淮南矿区为研 究对象，运用煤田地质学、煤层气地质学、采矿学、渗流力学、数学物理方法、 油气藏数值模拟技术等理论和方法，通过现场调研、理论研究、分析测试、储层 建模、数值模拟和工程试验，开展了采动区煤层气运移和产出规律、采动引起的 渗透率时空演化模式和采动区煤层气井产能数值模拟模型及模拟方法等研究工 作，开发出了煤矿采动区煤层气井抽采产能数值模拟软件，并将研究成果应用于 淮南矿区采动区煤层气井历史拟合和产能预测， 取得了以下主要研究成果和认识。 （1）揭示了采动区煤层气赋存、储集、运移和产出规律。随着采煤工作面 向前推进，采动引起上部岩层和煤层破坏断裂、离层卸压、漏水降压，煤层气解 吸扩散，进入采动裂隙中储集，继而在压力梯度作用下向采动区煤层气井渗流并 产出。 对淮南矿区24个工作面106口采动区煤层气井的生产数据分析结果显示， 与常规煤层气井明显不同，采动区煤层气井表现出独有的产气特征，即日产气量 成数倍至数十倍增大， 并且日气产量与时间的关系曲线呈现初期急剧增加直至最 大峰值、继而快速下降至最低水平后维持长时间稳定的“单尖峰拖长尾”典型形 态特征。 （2）研究发现，采动区井的日产气量与井到回采工作面的距离普遍呈良好 的相关性，并且其关系曲线也呈“单尖峰拖长尾”的典型形态特征，即当回采工 作面推进到超过煤层气井 5m 左右时，气产量才呈陡壁式急剧增加，一直到超过 煤层气井 50m 左右时达到最大峰值；随后随着工作面继续推进，气产量呈陡坡 式快速下降， 直至超过煤层气井 280m 左右时停止下降， 并且在 1000m 后仍维持 较高气产量。研究认为，采动区煤层气井呈现出的独有产气特征，主要是煤矿井 下回采工作面推进产生的扰动，使上部煤层和岩层遭受破裂卸压、强化增渗作用 和随之发生的重力压实作用，引起煤层渗透率呈几何数量级急剧增大，随后又快 速减小的结果；其次与上部煤层和岩层中水的快速漏失、泄压等因素影响有关。 （3）基于黑盒子理论和 Boltzmann 函数拟合，首次提出了采动区上部煤层 视渗透率随工作面推进位置到煤层气井之间距离变化的数学表达式。 由于采动区 上部煤层渗透率在平面上动态演化过程极其复杂， 很难用一个函数来全面真实地 万方数据 摘 要 2 表征， 为此采用采动区煤储层视渗透率来等效反映开采扰动下采动区上部煤层渗 透率对煤层气井产能的实际影响。 （4）建立了采动区煤层气井产能模拟的概化地质模型、三维两相数学模型 和数值模型，并给出了边界处理、数值求解和关键参数拟合求解方法。与常规煤 层气数值模拟模型和求解方法相比，具有如下特点一是回采工作面推进扰动形 成动边界条件，使采动区范围随时间变大；二是采动区内煤储层的渗透率、储层 压力、孔隙度等储层参数是动态变化的；三是煤层气井产气不排水，煤储层中的 水通过采动裂隙向下渗漏排出，实现储层降压。四是提出了煤储层视渗透率数学 表达式中形态控制参数和渗透率极值参数的求取方法， 即通过采动区煤层气井产 量与煤层气井到回采工作面距离的数据拟合求取煤储层视渗透率数学表达式中 的形态控制参数， 通过对采动区煤层气井产量数据进行历史拟合求取煤储层视渗 透率数学表达式中的渗透率极值参数。 （5）开发出了煤矿采动区煤层气井抽采产能数值模拟软件 CCGS v1.0，实 现了采动影响下煤层气井单井抽采产能的数值模拟。 基于常规煤层气产能数值模 拟软件 CBM-SIM，开发了具有对煤矿采动区煤层视渗透率、储层压力、漏失水 等煤储层动态参数进行集成、处理和赋值功能的专用计算机模块；创新了时间卡 中断刷参机制， 实现了在运算过程中按时间步暂停对煤储层动态参数进行自动更 新的功能； 形成了具备采动区煤层气井产能数值模拟和常规煤层气井产能数值模 拟的双功能软件平台。软件界面友好，操作灵活、使用方便。 （6）研究成果应用于淮南矿区潘一、潘三、顾桥、丁集和朱集等煤矿，对 8 个工作面 11 口采动区煤层气井进行了生产数据历史拟合和气产量数值模拟预测， 得到验证，取得了良好的应用效果。 关键词关键词采动区煤层气井 采动影响 煤储层 视渗透率表达式 产能数值模拟 软 件开发 万方数据 ABSTRACT i ABSTRACT Gob coal seam gas well extraction is a unique way of CBM development in coal mining area, and it is an important way to achieve high efficient surface methane drainage, especially in soft and low permeability coal seams, using the overburden rock to break down and release pressure produced by the mining of coal seam, to improve the permeability of the upper adjacent coal seam. It is also an effective measure to prevent gas overrun in the upper corner of the working face. However, for many years, the numerical simulation of gob coal seam gas well extraction productivity has always been a worldwide difficult problem. This paper is based on the “12th Five-Year“ National Science and Technology Major Project “prediction technology of coalbed methane production capacity in coal mine area 2011ZX05040-003“, takes the Huainan mining area of Anhui Province, which is exploited by coal seam group, as the research object, using the theory and of coal geology, coalbed gas geology, mining science, seepage mechanics, mathematical physics , oil and gas reservoir numerical simulation technology and so on, through field investigation, theoretical research, analysis test, reservoir modeling, numerical simulation and engineering test, the research work is carried out on the migration and output law of gob coal seam gas well extraction, the spatio-temporal evolution model of permeability caused by mining, the numerical simulation model and simulation of the gob coal seam gas well extraction, etc. A software for numerical simulation of gob coal seam gas well extraction productivity in coal mining area has been developed. The research results are applied to the history matching and productivity prediction of gob coal seam gas well extraction of Huainan mining area, and the following main research results and knowledge are obtained. 1 The law of occurrence, accumulation, migration and production of coalbed methane in mining area is revealed. With the continuous mining of working face, mining causes the upper strata and coal seam to break, fracture, release pressure ,leakage of stratum water and reservoir pressure drop. The coalbed methane desorption and diffusion enter the mining-induced fractures, and then flow and yield to gob coal seam gas well under the action of pressure gradient. The production data analysis of 106 gob coal seam gas wells of 24 working faces in Huainan mining area shows that it is obviously different from conventional CBM wells. The gob coal seam 万方数据 ABSTRACT ii gas wells show unique characteristics of gas production, and the daily gas production is multiplied by several times to dozens of times, and the relationship curve of the daily gas production and time increases rapidly in the early stage until the maximum peak, and then rapidly descends to the lowest level, and maintains a long time stability, it shows a typical characteristic of “single spike dragged long tail“. 2 It is found that there is a good correlation between the daily gas production of the gob coalbed methane well and the distance from the gob coalbed methane well to the working face. And its relationship curve also presents the typical morphological characteristics of the “ single spike dragged long tail “.That is, when the working face is pushed forward to more than 5m of the gob coal seam gas well, the gas output increases sharply in a steep wall, reaching the maximum peak when the working face exceeds the gob coal seam gas well about 50m, and the gas output decreases rapidly as the working face continues to advance until the gob coal seam gas well is overtaken 280m, and the higher gas production is still maintained after 1000m. The unique gas producing characteristics of the gob coal seam gas well are mainly due to the disturbance caused by the working face mining, which make the upper coal seam and rock strata break down and pressure relief, strengthen the infiltration and gravitational compaction, caused the permeability of upper coal seam to increase sharply in geometric magnitude, and then decrease rapidly. Secondly, it is related to the factors such as water rapid leakage and pressure relief of the upper coal seam and strata. 3 Because the dynamic evolution process of the upper coal seam permeability in the coal mine gob is very complicated, it is difficult to represent comprehensively and realistically with a function. Based on the black box theory and the Boltzmann function fitting, the mathematical expression of the variation of the apparent permeability of the upper coal seam in the coal mine gob with the distance between the working face and the gob coal seam gas well is proposed for the first time, which represents the equivalent permeability of the upper coal seam in the coal mine gob, to comprehensively reflect the actual influence of coal seam permeability on coalbed methane well productivity under mining disturbance. 4 The generalized geological model, three-dimensional two-phase mathematical model and numerical model of gob coal seam gas well productivity simulation are established. And the of boundary treatment, numerical solution and key parameter fitting is given. Compared with the conventional CBM numerical simulation model and solution , it has the following characteristics first, the mining 万方数据 ABSTRACT iii disturbance of the working face causes the dynamic boundary condition, which makes the range of the mining area larger with time; second, the reservoir parameters of the upper coal seam in the mine gob such as permeability, reservoir pressure and porosity are dynamically changed; third, the production of gas in the CBM well is undrained, and the water in the coal reservoir is leaked down through the mining fissure , resulting in reservoir pressure drop; fourth, the of obtaining the morphological control parameters and the permeability extremum parameters in the mathematical expression of the coal reservoir apparent permeability is put forward, that is to obtain the morphological control parameters in the mathematical expression of the coal reservoir apparent permeability through the data fitting of the gob coal seam gas well production and the distance from the well to the working face, to obtain the permeability extremum parameter in the mathematical expression of apparent permeability of coal reservoir by fitting the production data of gob coal seam gas well. 5 The numerical simulation software CCGS v1.0 for the production capacity of gob coal seam gas well is developed, which has realized the numerical simulation of single well pumping productivity affected by the mining action. Based on the conventional CBM capacity numerical simulation software CBM-SIM, a special computer module has been developed to integrate, process and assign the dynamic parameters of coal seam permeability, reservoir pressure, leakage of water in the upper coal seam of gob. The mechanism of time card interrupting and renovating parameter is innovated, and the function of automatically updating the dynamic parameters of coal reservoir in time step is realized in the operation process. A dual function software plat for gob coal seam gas well productivity numerical simulation and conventional CBM well productivity numerical simulation is ed. The software has friendly interface, flexible operation and convenient operation. 6 The research results are applied to the coal mines of Pan Yi Mine, the Pan San Mine, the Gu Qiao Mine, the Ding Ji Mine and the Zhu Ji Mine, in Huainan mining area. The production data history fitting and the gas production numerical simulation prediction are carried out on 11 gob coal seam gas wells of 8 working faces, the results have been verified and good application results have been obtained. Key Words gob coal seam gas well; mining influence; coalbed reservoir; apparent permeability; productivity numerical simulation; software development 万方数据 万方数据 目 录 i 目目 录录 第 1 章 绪论 .......................................................................................... i 1.1 选题意义 ...................................................................................................... 1 1.2 研究现状 ...................................................................................................... 2 1.2.1 煤矿采动区煤层气开发相关理论及实践 ................................................................... 2 1.2.2 煤层气开发数值模拟研究 ........................................................................................... 6 1.3 论文研究目标、内容和技术路线 ...............................................................10 1.3.1 研究目标 ..................................................................................................................... 10 1.3.2 主要研究内容 ............................................................................................................. 11 1.3.3 技术路线 ..................................................................................................................... 11 第 2 章 煤矿采动区煤层气井产气机理 ............................................ 12 2.1 未受采动影响的煤层气储集、运移和产出机理 ........................................12 2.2 采动对煤层气产出的影响分析 ...................................................................14 2.2.1 采动影响后煤储层应力的变化 ................................................................................. 14 2.2.2 采动影响后煤储层结构形态的变化 ......................................................................... 21 2.3 淮南矿区采动区煤层气井生产曲线特征及原因分析 ................................25 2.3.1 采动区煤层气井生产曲线特征 ................................................................................. 25 2.3.2 采动区井与常规煤层气井产气特征差异性分析 ..................................................... 31 2.4 本章小结 .....................................................................................................33 第 3 章 煤矿采动区煤层气井产能数值模拟模型 ............................. 34 3.1 采动区煤储层的视渗透率量化表征和泄水降压处置方法 ........................34 3.1.1 采动区煤储层的视渗透率量化表征 ......................................................................... 34 3.1.2 采动区煤储层泄水降压处置方法 ............................................................................. 42 3.2 地质模型的建立 ..........................................................................................46 3.2.1 理想模型分析 ............................................................................................................. 46 3.2.2 地质模型概化 ............................................................................................................. 48 3.3 数学模型的建立 ..........................................................................................49 3.3.1 煤基质块微孔隙系统 ................................................................................................. 49 3.3.2 采动影响的裂隙系统 ................................................................................................. 50 3.3.3 辅助方程 ..................................................................................................................... 54 3.3.4 定解条件 ..................................................................................................................... 54 3.3.5 采动影响煤储层模拟数学模型 ................................................................................. 55 万方数据 目 录 ii 3.4 数值模型的建立 ..........................................................................................56 3.4.1 离散差分 ..................................................................................................................... 56 3.4.2 建立差分方程 ............................................................................................................. 57 3.5 差分方程求解 ..........