煤矿井下射孔导向压裂与递进排采技术研究及应用.pdf

煤矿井下射孔导向压裂 与递进排采技术研究及应用 重庆大学博士学位论文 学生姓名李 栋 指导教师卢义玉 教 授 副 导 师沈大富 教授级高工 黄昌文 教授级高工 领 域能源与环保 类 别工程 重庆大学资源及环境科学学院 二 O 一八年九月 万方数据 万方数据 Research and Application of Perforating -guided Hydraulic Fracturing and Progressive Drainage Technology in Underground Coal Mine A Thesis ted to Chongqing University in Partial Fulfillment of the Requirement for the Doctor’s Degree of Engineering By LI Dong Supervised by Prof. Lu Yiyu Assistant Supervised by Prof. Shen Dafu Prof. Huang Changwen Field Energy and Environmental Protection College of Resources and Environmental Sciences of Chongqing University, Chongqing, China September 2018 万方数据 万方数据 中文摘要 I 摘 要 作为煤炭生产和消费大国，我国煤层气（煤层瓦斯）资源十分丰富，但瓦斯 灾害却也是煤矿安全生产的“第一杀手”，此外，瓦斯排空对生态环境亦造成了极 强的破坏。近年来，用于油气储层改造的水力压裂技术被引入到煤矿井下煤层增 透工程中，取得了一定成效，但由于煤层增透与油气储层改造之间存在的诸多差 异，导致煤矿井下水力压裂难以直接援用油气井水力压裂理论与装备。在工程实 践中，水压裂缝扩展形态不理想和闭合过早，大幅降低了煤层增透效果和瓦斯抽 采效率，同时还给压裂和采掘作业带来了重大安全隐患，严重阻碍了该技术在煤 矿井下的推广应用。为此，本文提出了煤矿井下射孔引导水压裂缝起裂及扩展， 再沿主裂缝方向遵循压降传递时空规律依次布设多级钻孔实施排采，延缓裂缝闭 合，促进瓦斯运移产出的新方法。 该方法实现高效抽采煤层瓦斯的关键在于裂缝定向起裂、有序扩展及排采作 业时空衔接合理，为此本文拟开展以下研究①射孔导向压裂裂缝起裂及扩展规 律；②射孔导向压裂瓦斯运移规律及递进排采；③煤矿井下射孔导向压裂与递进 排采系统；④煤矿井下射孔导向压裂与递进排采现场试验。主要取得以下成果 （1）在分析了煤矿井下水力压裂特点的基础上，提出了射孔引导水压裂缝定 向起裂、有序扩展的方法；考虑了地应力场、瓦斯压力、钻孔内水压力及高压水 向煤层滤失等多个因素，采用叠加原理和最大拉应力准则，构建了射孔导向作用 下裂缝起裂压力、起裂角的力学模型及计算步骤；采用拉剪复合型破坏判据和最 大周向应力理论，建立了裂缝扩展临界水压和裂缝延伸角的力学模型及计算步 骤，并通过工程实例计算和数值模拟验证了模型的正确性。 （2）揭示了射孔导向下水压裂缝的起裂及扩展规律射孔导向下的煤体起裂 压力较常规水力压裂下降 30，各射孔参数对起裂压力影响程度不一射孔孔径 对其影响较小，起裂压力随射孔深度在 01.5 倍孔径范围内增长而大幅下降，射 孔方位角对其影响则呈现出明显的阶段性。射孔导向压裂经历了应力累积、裂缝 起裂及沿射孔方向扩展、裂缝转向扩展和裂缝沿最大主应力方向扩展四个阶段。 裂缝起裂位置及扩展形态取决于垂直于最大主应力平面上两个主应力的差值 （）和射孔方位角（），任意条件下均存在一临界射孔方位角（ C ）， 当 C 时，裂缝在射孔孔眼尖端起裂并沿射孔方向扩展，但会逐渐转向到最大 主应力方向，转向距离随增大而增大；当 C 时，裂缝在钻孔壁面上起裂并 沿最大主应力方向扩展形成一条规则的双翼平直裂缝；当 C 时，裂缝在射孔 万方数据 重庆大学博士学位论文 II 孔眼尖端和钻孔壁面上同时起裂，在钻孔两侧分别形成单翼弯曲裂缝和沿最大主 应力方向扩展的单翼平直裂缝，越大， C 越小，更容易形成多裂缝形态。 （3）射孔导向压裂形成了包括宏观裂隙区、微裂隙贯通区和微裂隙产生区的 椭圆形有效影响范围，分析了瓦斯在此空间内的运移规律注水过程中高压水进 入煤基质使煤层含水率增大，钻屑瓦斯解吸指标 K1值和吸附常数 a 随之呈对数函 数减小，抑制了吸附瓦斯的解吸，而且注水时间越长该抑制效果越明显，同时高 压水随裂缝扩展驱赶游离瓦斯逐步向煤层深部运移，在压裂有效影响范围至其外 推约 5m 的环形空间形成瓦斯富集带；排水过程中煤层压力不断下降，沿主裂缝方 向压降传递最有效，优先降至临界瓦斯解吸压力启动解吸，瓦斯渗透率提升最为 明显。在此基础上提出了沿主裂缝方向遵循压降传递时空规律递进布置多级钻孔 实施排采，延缓裂缝闭合，促进瓦斯运移产出的排采方法。 （4）研发出适用于煤矿井下的轮式车载定位钻机、高压泵组、水力射孔器、 高承压胶囊封隔器、气体射流泵排采装置及抽采孔带压快速密封装置等射孔导向 压裂与排采系统装备；构建了回采工作面和石门揭煤压裂岩柱最小安全厚度模型 及压裂孔最优布置间距模型 12 2 42 2 21cos2 L LL mm dkc  ，优化了布孔、射孔、 封孔、压裂、裂缝监测及排采等核心工艺，构建了包括压裂区地质预报、岩柱注 浆加固、孔口防反冲及安全监测等的安全防控体系。 （5）现场试验表明与常规水力压裂和抽采相比，采用新工艺后煤体起裂压 力明显降低，裂缝起裂及扩展受射孔导向显著，并有效弱化了高压水对顶底板的 损伤破坏，压裂有效影响范围扩大了 35以上，瓦斯抽采浓度提高了 1520 个百 分点，平均单孔瓦斯抽采纯量提高 2.73 倍，煤层瓦斯抽采率提高 14.2 个百分点， 钻孔工程量节省 40，大幅缩短了瓦斯抽采达标时间，并基本杜绝了喷孔和瓦斯 超限等现象。将该技术推广应用至西南地区三十余座矿井和瓦斯隧道的低透气性 煤层增透工程中，保障了煤矿安全生产，提高了煤层气开发利用率，减少了对生 态环境的破坏，产生了良好的经济和社会效益。 关键词关键词煤矿井下，射孔导向，水力压裂，裂缝扩展，瓦斯运移，递进排采 万方数据 英文摘要 III ABSTRACT As a big country in coal production and consumption, Chinas CBM resource is very rich, but the gas is also the chief killer of coal mine production. In addition, the gas discharging cause great damage to the ecological environment. In recent years, the hydraulic fracturing used to increase the permeability of hydrocarbon reservoirs was introduced into gas drainage of seam in underground coal mines. However, because of the differences between the coal seam and the hydrocarbon reservoirs, the hydraulic fracturing theory and equipment for hydrocarbon reservoirs can not be used directly in underground coal mine. The cracks expansion irregular, cracks closure prematurely, and the instability of safety pillar often occur in engineering. Which have greatly reduced the enhancement effect and gas drainage efficiency, and also brought hidden danger to fracturing and mining operation, which seriously hindered the application of hydraulic fracturing in underground coal mines. Therefore, this thesis proposes a new to delay the closure of fracturing cracks and promote the production of gas migration by perforating-guided and progressive drainage. The key to extract gas efficiently by this lies in the crack orderly expansion and the reasonable connection between the drainage holes. The main research contents and achievements are as follows 1 Based on the analysis of the characteristics of hydraulic fracturing in coal mines, considering the ground stress field, gas pressure, water pressure in the borehole, and fluid loss from the high pressure water to the coal seam, the crack initiation pressure, initiation angle mechanical model and calculation steps of perforating-guided fracturing cracks are constructed by superposition principle and maximum tensile stress criterion. The critical hydraulic pressure and crack extension angle mechanical model and calculation steps for crack propagation are established by shear-shear composite failure criterion and maximum circumferential stress theory. The correctness of the model is verified by engineering example calculation and numerical simulation. 2 The crack initiation and propagation law of hydraulic cracks under perforation guidance are revealed. The cracking pressure of coal guided by perforation is 30 lower than that of conventional hydraulic fracturing. The perforation parameters have different effects on the cracking pressure the perforation pore size has little effect on it, and the cracking pressure decreases rapidly with the perforation depth increasing from 0 万方数据 重庆大学博士学位论文 IV to 1.5 times the diameter of the hole, while the perforation azimuth has a significant stage effect. Perforation fracturing undergoes four stages of stress accumulation, crack initiation and expansion along the perforation direction, crack propagation and crack propagation along the direction of the maximum principal stress. The crack initiation position and the extended shape depend on the difference between the two principal stresses  perpendicular to the maximum principal stress plane and the perforation azimuth angle .There is a critical perforation azimuth 0  in any combination. When  0, the crack starts at the tip of the perforation and expands in the direction of the perforation, but gradually turns to the direction of the maximum principal stress, and the steering distance increases with increases. When  0, the crack cracks on the wall of the borehole and expands along the direction of the maximum principal stress to a regular double-wing straight crack. When  0 , the crack simultaneously cracks at the tip of the perforating hole and the wall surface of the borehole, and a single-wing curved crack and a single-wing straight crack extending along the direction of the maximum principal stress are respectively ed on both sides of the borehole. The larger  is, the smaller 0  is, the more easily to s a multi-crack morphology. 3 The perforating-guided fracturing s an elliptical effective influence range including a macro-fracture zone, a micro-fracture penetration zone and a micro-fracture zone in the coal seam. The law of gas migration in this space is analyzed the high-pressure water enters the coal matrix to increase the moisture content of the coal seam during the water injection process. The drill cuttings gas desorption index K1 and adsorption constant a decrease logarithmically, and the adsorption gas desorption is inhibited. Moreover, the longer the water injection time, the more obvious the inhibition effect. At the same time, the high-pressure water drives the free gas to the deep coal seam, ing a gas enrichment zone in the range of 3345m from the fracturing hole. At the same time, the high-pressure water drives away the dissociative gas to the deep coal seam, ing a gas enrichment zone between the annular effective space line of hydraulic fracturing and push it 5m out. During the drainage process, the pressure of the coal seam is continuously decreasing. But the pressure drop along the main crack direction is most effective, and priority reduce to the critical gas desorption pressure to initiate desorption, and the gas permeability increase is most obvious. On this basis, a to delay the crack closure and promote gas migration output by progressively arranging multi-stage drilling along the direction of the main crack in accordance with 万方数据 英文摘要 V the pressure drop transmission law is proposed. 4 The perforating-guided fracturing and progressive drainage system equipment include wheeled vehicle positioning drilling rigs, high pressure pump sets, hydraulic perforators and gas jet pump drainage devices suitable for underground coal mines is developed. The minimum safe thickness model of hydraulic fracturing rock column and the optimal placement distance model of fracturing hole are constructed. A high pressure capsule packer and a pressure quick sealing device are respectively developed for the fracturing hole and the drainage hole. Optimized process parameters suah as sealing, perforating, fracturing, crack monitoring and drainage, and the safety prevention and control system for fracturing area geological prediction, rock column grouting reinforcement, orifice anti-backlash and safety monitoring was constructed. 5 The field test shows that compared with the conventional process, the cracking pressure of the coal under the perforation guidance is significantly reduced, the crack initiation and expansion are significantly guided by the perforation, and the damage of the high pressure water to the surrounding rock are effectively weakened, and the effective influence range is expanded more than 35. In addition, the gas drainage concentration increased by 1520, the average single-hole gas extraction smelter increased by 2.73 times, the coal seam gas drainage rate increased by 14.2, and the drilling engineering volume saved by 40. The gas extraction time has been greatly shortened, and put an end to the phenomenon of gas blasting over limit. The technology was applied to over 30 mines and gas tunnels in the southwestern region, which ensured the safe production of coal mines, improved the development and utilization rate of coalbed methane, reduced the damage to the ecological environment, and produced good economic and social benefits. Key words underground coal mine, perforating -guided, hydraulic fracturing, crack propagation, gas migration, progressive drainage 万方数据 重庆大学博士学位论文 VI 万方数据 目 录 VII 目 录 中文摘要中文摘要 .......................................................................................................................................... I 英文摘要英文摘要 ....................................................................................................................................... III 1 绪绪 论论 ...................................................................................................................................... 1 1.1 研究目的及意义研究目的及意义 ....................................................................................................................... 1 1.2 研究现状及存在问题研究现状及存在问题 ............................................................................................................... 2 1.2.1 水力压裂裂缝扩展规律及导控方法 ................................................................................. 2 1.2.2 水力压裂对瓦斯运移规律影响研究 ................................................................................. 6 1.2.3 煤矿井下水力压裂配套装备及安全保障 ......................................................................... 8 1.2.4 存在的主要问题 ................................................................................................................. 9 1.3 研究内容、方法及技术路线研究内容、方法及技术路线 ................................................................................................. 10 1.3.1 研究内容 ........................................................................................................................... 10 1.3.2 技术路线 ........................................................................................................................... 11 2 煤矿井下射孔导向压裂裂缝扩展规律煤矿井下射孔导向压裂裂缝扩展规律 ............................................................... 13 2.1 煤矿井下射孔导向压裂煤矿井下射孔导向压裂方法方法 ................................................................................................. 13 2.1.1 煤矿井下水力压裂特点 ................................................................................................... 13 2.1.2 煤矿井下射孔导向压裂方法 ........................................................................................... 14 2.2 射孔导向压裂钻孔应力分布射孔导向压裂钻孔应力分布 ................................................................................................. 15 2.2.1 水力射孔模型 ................................................................................................................... 15 2.2.2 常规水力压裂钻孔应力分布 ........................................................................................... 16 2.2.3 水力射孔孔眼应力分布 ................................................................................................... 19 2.3 射孔导向压裂裂缝起裂及扩展模型射孔导向压裂裂缝起裂及扩展模型 ..................................................................................... 20 2.3.1 常规水力压裂裂缝起裂压力及角度 ............................................................................... 20 2.3.2 射孔导向压裂裂缝起裂压力及角度 ............................................................................... 22 2.3.3 射孔导向压裂裂缝转向扩展模型 ................................................................................... 22 2.4 射孔导向压裂裂缝起裂及扩展规律射孔导向压裂裂缝起裂及扩展规律 ..................................................................................... 24 2.4.1 数值模型及参数 ............................................................................................................... 24 2.4.2 水力射孔对起裂压力影响 ............................................................................................... 25 2.4.3 水力射孔对裂缝转向扩展影响 ....................................................................................... 28 2.5 本章小结本章小结 ................................................................................................................................. 35 3 煤矿井下射孔导向压裂瓦斯运移规律及递进排采方法煤矿井下射孔导向压裂瓦斯运移规律及递进排采方法.......................... 37 3.1 外加水分对瓦斯解吸影响实验外加水分对瓦斯解吸影响实验 ............................................................................................. 37 万方数据 重庆大学博士学位论文 VIII 3.1.1 实验方案 ........................................................................................................................... 37 3.1.2 吸附平衡压力对瓦斯解吸的影响 ................................................................................... 38 3.1.3 外加水分对瓦斯解吸量的影响 ....................................................................................... 40 3.1.4 外加水分对瓦斯解吸速度的影响 ................................................................................... 46 3.1.5 外加水分对解吸指标 K1 的影响 .................................................................................... 48 3.2 外加水分对瓦斯渗流影响实验外加水分对瓦斯渗流影响实验 .....................................................