Theoretical analysis and engineering application of controllable shock wave technology for enhancing coalbed methane in soft and low‑permeability coal seams

Coalbed methane(CBM)is a significant factor in triggering coal and gas outburst disaster,while also serving as a clean fuel.With the increasing depth of mining operations,coal seams that exhibit high levels of gas content and low permeability have become increasingly prevalent.While controllable shockwave(CSW)technology has proven effective in enhancing CBM in laboratory settings,there is a lack of reports on its field applications in soft and low-permeability coal seams.This study establishes the governing equations for stress waves induced by CSW.Laplace numerical inversion was employed to analyse the dynamic response of the coal seam during CSW antireflection.Additionally,quantitative calculations were performed for the crushed zone,fracture zone,and effective CSW influence range,which guided the selection of field test parameters.The results of the field test unveiled a substantial improvement in the gas permeability coefficient,the average rate of pure methane flowrate,and the mean gas flowrate within a 10 m radius of the antireflection borehole.These enhancements were notable,showing increases of 3 times,13.72 times,and 11.48 times,respectively.Furthermore,the field test performed on the CSW antireflection gas extraction hole cluster demonstrated a noticeable improvement in CBM extraction.After antireflection,the maximum peak gas concentration and maximum peak pure methane flow reached 71.2%and 2.59 m^(3)/min,respectively.These findings will offer valuable guidance for the application of CSW antireflection technology in soft and low-permeability coal seams.

Theory of gas extraction from coal seams and its use

Gas extraction is one of the main measures of control and use of gas of coal mines. At present, the design method is under the experimental period and do not satisfy the need of practice. In this paper, the theory of gas extraction of coal seams based upon Darcy law was studied. Mathematical model of gas extraction of coal seams was established and two kinds of solv- ing approaches based on computer software and linear approximation were given. The rightness and the validities of the model were examined with a practical example. Results obtained can be used to determine and optimize the parameters related etc.

Application of deep borehole blasting on fully mechanized hard top-coal pre-splitting and gas extraction in the special thick seam

In order to solve the problems of top-coal inadequate destruction and large amounts of gas emission in mining extra thick and hard coal seam,this study investigated the pre-splitting for deep borehole blasting and gas pre-draining technologies on top coal.The mechanism of the technologies was systematically expounded based on hard top-coal cracks development obtained by numerical simulation and theoretical analysis.The results show that explosive blasting in the hard rock results in a large number of cracks and large displacement in the rock mass due to the effect of explosion stress.Meanwhile,the thick top-coal caves,and desorbing gas flows along the cracks improve gas extraction.Finally,the pre-splitting for deep borehole blasting and gas pre-draining technologies was applied in No.3802 working face of Shui Liandong Coal Mine,which increases monthly output in the face to 67.34 kt and the drained gas concentration to 86.2%.The drained gas average concentration from each borehole reaches 40%,and the effect is remarkable.

Technique of coal mining and gas extraction without coal pillar in multi-seam with low permeability

Aimed at the low mining efficiency in deep multi-seams because of high crustalstress,high gas content,low permeability,the compound 'three soft' roof and the trouble-somesafety situation encountered in deep level coal exploitation,proposed a new idea ofgob-side retaining without a coal-pillar and Y-style ventilation in the first-mined key pressure-relieved coal seam and a new method of coal mining and gas extraction.The followingwere discovered:the dynamic evolution law of the crannies in the roof is influenced bymining,the formative rule of 'the vertical cranny-abundant area' along the gob-side,thedistribution of air pressure field in the gob,and the flowing rule of pressure-relieved gas ina Y-style ventilation system.The study also established a theoretic basis for a new miningmethod of coal mining and gas extraction which is used to extract the pressure-relievedgas by roadway retaining boreholes instead of roadway boreholes.Studied and resolvedmany difficult key problems,such as,fast roadway retaining at the gob-side without a coalpillar,Y-style ventilation and extraction of pressure-relieved gas by roadway retainingboreholes,and so on.The study innovated and integrated a whole set of technical systemsfor coal and pressure relief gas extraction.The method of the pressure-relieved gasextraction by roadway retaining had been successfully applied in 6 typical working faces inthe Huainan and Huaibei mining areas.The research can provide a scientific and reliabletechnical support and a demonstration for coal mining and gas extraction in gaseous deepmulti-seams with low permeability.

Definition, theory, methods, and applications of the safe and efficient simultaneous extraction of coal and gas

Simultaneous extraction of the coal and gas is an effective method of eliminating coal mine gas disasters while safely exploiting the coal and achieving efficient gas drainage in China, which is widely accepted by the main coal-producing countries around the world. However, the concrete definition of simultaneous extraction is vague and there is little accurate theoretical support for the simultaneous extraction of coal and gas, which makes it difficult to determine an efficient gas drainage method appropriate to the features of coal seams. Based on theoretical analysis, laboratory tests and field observations, a specific definition of simultaneous extraction of coal and gas is proposed after analyzing the characteristics of coal seam occurrences in China, and we developed the mechanism of mining-enhanced permeability and established the corresponding theoretical model. This comprises a process of fracture network formation, in which the original fractures are opened and new fractures are produced by unloading damage. According to the theoretical model, the engineering approaches and their quantitative parameters of ＇unloading by borehole drilling＇ for single coal seams and ＇unloading by protective seam mining＇ for groups of coal seams are proposed, and the construction principles for coal exploitation and gas-drainage systems for different conditions are given. These methods were applied successfully in the Tunlan Coal Mine in Shanxi Province and the Panyi Coal Mine in Anhui Province and could assure safe and efficient simultaneous extraction of coal and gas in these outburst coal mines.

Progress on the hydraulic measures for grid slotting and fracking to enhance coal seam permeability

A method of hydraulic grid slotting and hydraulic fracturing was proposed to enhance the permeability of low permeability coal seam in China. Micro-structural development and strength characteristics of coal were analysed to set up the failure criterion of coal containing water and gas, which could describe the destruction rule of coal containing gas under the hydraulic measures more accurately. Based on the theory of transient flow and fluid grid, the numerical calculation model of turbulence formed by high pressure oscillating water jet was used. With the high speed photography test, dynamic evolution and pulsation characteristics of water jet water analysed which laid a foundation for mechanism analysis of rock damage under water jet. Wave equation of oscillating water jet slotting was established and the mechanism of coal damage by the impact stress wave under oscillation jet was revealed. These provide a new method to study the mechanism of porosity and crack damage under high pressure jet.Fracture criterion by jet slotting was established and mechanism of crack development controlled by crack zone between slots was found. The fractures were induced to extend along pre-set direction,instead of being controlled by original stress field. The model of gas migration through coal seams after the hydraulic measures for grid slotting and fracking was established. The key technology and equipment for grid slotting and fracking with high-pressure oscillating jet were developed and applied to coal mines in Chongqing and Henan in China. The results show that the gas permeability of coal seam is enhanced by three orders of magnitude, efficiency of roadway excavation and mining is improved by more than 57%and the cost of gas control is reduced by 50%.

Influence of Water Injection Fracturing on Crack Damage in Soft Coal and Application in Gas Extraction

In order to study the hypotonic and rheological particularity of “three soft” coal seam in west Henan, China, this paper explored the stress and damage characteristics of crack in coal under condition of water injection fracturing based on ABAQUS platform;The cohesive element in T-P damage evolution criterion was used to describe the approximately linear relationship between crack width and extending distance in soft coal. The simulation results show that stress evolution and crack damage in soft coal is a gradually developing process under condition of water injection fracturing. When the static pressure is 4 - 10 MPa, and the injection time is about 1 - 2 hours, the damage range of crack in soft coal can basically reach an ideal data of 80 - 100 m, and then greatly improve the hypotonic performance of “three soft” coal seam.

Prediction of methane emissions during the extraction of close-to-roof layer of a seam of large thickness

Prediction of methane emissions at the stage of longwall planning constitutes the basis for the determination of the appropriate method and parameters of ventilation and selection of prevention means including the methane drainage technol- ogy. The growth of methane saturation of coal seams with the extraction depth, with simultaneously increasing output concen- tration, contributes to the increase of the quantity of methane emitted into longwall areas. The subject matter of the article has been directed at the predicted quantity of methane emissions into planned longwalls with roof caving in the layer of seams adjacent to the roof of large thickness. The performed prognostic calculations of methane emissions into the longwall working were referred to two sources, i.e. methane liberated during coal mining by means of a cutter-loader and methane originating from the degasification of the floor layer destressed by the longwall conducted in the close-to-roof layer. The calculations of predictions allow to refer to the planned longwall, on account of the emitting methane, with possible and safe output quantity. Planning of extraction in the close-to-roof layer of a seam of large thickness with roof caving is especially important in con- ditions of increasing methane saturation with the depth of deposition and should be preceded by a prognostic analysis for de- termining the extraction possibilities of the planned longwall.

重复注气压降法煤层渗透率模型与原位测试研究

煤层渗透率作为衡量瓦斯渗流与抽采难易程度的重要指标,对其进行准确测定具有重要意义。针对现有方法计算渗透率测试周期长、结果不稳定、模型不完善等问题,研究煤层渗透率的快速准确测定方法及相应的计算模型。基于煤层中气体径向不稳定流控制方程,结合不同压差下气体在煤层中的体积流量方程,建立可利用全区间压降数据测定煤层渗透率的注气压降计算模型。应用COMSOL数值模拟软件的达西渗流模块对模型进行求解,针对现场工程设计中可对压降曲线产生影响的测压气室长度进行单变量处理,根据模拟结果分析钻孔的测压气室长度可设计为2.0 m。根据数值模拟结果进行现场布置,搭建井下重复注气压降试验系统,结合煤层瓦斯赋存条件和巷道条件施工两组穿层钻孔,对2个测点分别注入两次高于煤层瓦斯压力的补偿气体进行渗透率原位测试,测试周期分别约为6 d和17 d,第2轮测试的注气压力高于第1轮。结合理论推导验证了注气压降过程中煤层瓦斯的雷诺数均处于线性达西渗流段,瓦斯在煤层中的渗流符合达西定律,满足计算模型的假设。与传统煤层渗透率计算方法进行了比较,结果表明:本方法和径向流量法的计算结果基本一致,可以满足实际工程需要。重复注气压降法的测试结果稳定可靠,具备快速测定的优点。

开采保护层与预抽煤层瓦斯防突效果分析

为比较开采保护层与预抽煤层瓦斯防突效果,以1124(3)运顺开采保护层段和预抽煤层瓦斯段煤巷掘进为试验对象,统计了试验地点煤巷掘进期间残余瓦斯含量、钻屑瓦斯解吸指标K1、钻屑量等防突指标,采用假设检验方法推断了各防突指标是否有差别,分析了开采保护层段和预抽煤层瓦斯段各防突指标产生差别的原因,验证了开采保护层区域防突措施比预抽煤层瓦斯区域防突措施更加安全可靠。

平顶山矿区多煤层卸压立体抽采模式与工程示范

平顶山矿区多煤层发育、含气层段多,仅靠井下进行瓦斯治理工程量大、难度高。为了开辟平顶山矿区瓦斯抽采新模式,达到“采一层抽多层”的目的,采用气测录井与含气量测试相结合的方法精准判识了煤系主要含气层段和含气量;采用体积法评价了东部5对矿井采动区和采空区的煤系气资源量。基于“O”形圈理论和“防-抗-让”思想,分别优化设计了采动井、采空井的井位、层位和井身结构,构建了采动区、采空区多煤层卸压立体抽采模式并进行了工程示范。结果表明:(1)二_(1)煤层顶板200 m范围内存在四煤组、三煤组、二_(1)煤层顶板60 m范围内的砂岩/泥质砂岩互层段等3处主要含气段。平顶山矿区东部5对矿井的采动区和采空区资源量分别为26.36×10~8 m^(3)和20.00×10~8 m^(3)。(2)采动井最佳井位为0.17~0.28倍采长,且靠近回风巷条带区域;走向上,采动井的间距一般为80~100 m。创建了“大口径、避开岩体变形强烈区、P110梯型扣套管”的采动直井稳孔技术体系和“下行水平轨迹+提高套管强度”的采动L型水平井稳产技术体系,保证了产气通道的畅通性。采空井一般布置在距离回风巷30~50 m的区域,完钻位置一般为二_(1)煤层顶板40~60 m的范围;筛管布置在四煤段顶板至裂隙带底部。(3)建立了“地面采动直井/定向井-采动L型水平井-采空井”联作的卸压立体抽采模式,实现了多气源立体抽采。截至2024年4月30日,累计抽采纯量达5258.8万m^(3),总利用量达到3735.4万m^(3),率先在河南省实现了煤系气产业化开发,示范和引领带动作用显著。

自激振荡脉冲SC-CO_(2)射流冲击频率调制

SC-CO_(2)射流钻完井技术能保证煤层气井稳定性、提高钻井速度和破岩效率,具有广泛的应用前景。但较高的破煤能耗和复杂的系统限制了其工程推广,自激振荡脉冲SC-CO_(2)射流冲击频率和煤岩体的固有频率相同或满足相位关系,能充分发挥谐振效应,达到更好的破煤效果。喷嘴结构是影响射流冲击频率的关键,现有的自振脉冲水射流频率调制方法并不适用于SC-CO_(2)射流。为实现对SC-CO_(2)射流冲击频率的调制,采用大涡模拟研究不同喷嘴结构对自激振荡脉冲SCCO_(2)射流冲击频率的影响规律,通过权重分析得到不同喷嘴结构参数对射流冲击频率的影响程度。采用射流冲击频率测定实验及破煤实验验证喷嘴结构对射流冲击频率的影响规律以及射流冲击频率调制方法的可靠性。结果表明:振荡腔直径、振荡腔长度、碰撞壁角度是影响射流冲击频率的关键因素,可通过调节振荡腔结构实现对射流冲击频率的大幅调制,从而达到谐振效应。调节振荡腔结构使射流冲击频率与煤的固有频率形成谐振时破煤效果显著提升,且谐振倍数越小,射流破煤效果越好,能够有效提高破煤效率。当煤的固有频率是25 Hz时,设置上游和下游喷嘴出口直径为2.5、3.0 mm,调节振荡腔直径、长度、角度分别为10 mm、3 mm、120°,射流冲击频率达到25051.83 Hz,是煤体固有频率的1002.0倍,与煤的固有频率形成谐振效应,有效提高了破煤效率。

基于两堵两注通管直连技术的瓦斯抽采研究

为解决“两堵一注”封孔工艺及传统连管方式在孟津煤矿实施存在的弊端,提出了“两堵两注”通管直连技术,提高了瓦斯抽采浓度,延长了瓦斯抽采时间。为此,采用巷道松动圈理论分析了该矿合适的封孔长度;采用离散元数值模拟方法建立巷道模型,分析了巷道周围应力分布,确定了钻孔的最佳封孔深度;开展了“两堵两注”封孔地面实验和通管直连技术现场实验。结果表明:孟津煤矿二1煤层工作面顺层瓦斯抽采钻孔封孔长度至少为6.75 m;该矿12070工作面穿层钻孔最佳封孔深度为15~30 m;“两堵两注”技术能有效对抽采钻孔进行封堵;通管直连技术在现场应用中大幅度提高了瓦斯抽采浓度,延长了瓦斯抽采时间。

特厚煤层掘进巷道两帮卸压钻孔合理参数数值模拟研究

目前钻孔卸压技术为冲击地压矿井巷道掘进期间防冲主要措施之一,钻孔布置和参数决定着卸压效果。目的为了探讨特厚煤层掘进巷道两帮卸压钻孔合理布置参数,方法基于耿村煤矿综放工作面运输巷道地质采矿条件,利用数值计算方法研究掘进巷道两帮在单排布置时孔深、孔径、孔间距,双排布置时排距等不同参数条件下,巷道围岩应力云图和两帮垂直应力分布特征。结果结果表明:(1)单排布置卸压钻孔时,随着孔深、孔径递增,巷道两帮高应力区逐渐向深部围岩转移,而巷道两帮浅部围岩处于低应力区。(2)当钻孔孔深、孔径达到一定值时,巷道两帮支承压力由“单峰型”转化为“双峰型”,浅部围岩处于临界卸压状态;随着孔深、孔径继续增加,巷道两帮处于过度卸压状态。(3)利用卸压后、无卸压时巷道两帮高应力区向深部围岩的转移量ΔL、峰值应力处距巷道表面距离的比值η表示临界卸压和过度卸压状态,确定出卸压钻孔的合理参数。在耿村煤矿13230综放工作面运输平巷进行超前钻孔卸压和锚网索+36U型可缩性金属支架二级支护后,对巷道两帮实施钻孔卸压防冲,效果显著。结论研究结果对冲击地压矿井回采巷道掘进期间的卸压防冲具有指导和借鉴意义。

松软煤层底板爆破致裂增透模拟试验研究及应用

针对松软煤层爆破增透钻孔施工困难,爆破增透产生的裂隙不发育且易于重新压实的问题,提出在底板岩层开展爆破作业,达到松软煤层增透进而增加瓦斯有效抽采时间的目的。为了监测跨界面应力波传播规律及煤层损伤状况,在实验室构建了物理模型并开展了煤层底板爆破相似模拟试验。同时使用数值模拟的研究方法对煤层底板爆破过程中煤、岩体内部的损伤及裂隙的演化过程进行补充。结果表明:松软煤层底板爆破裂纹沿爆破孔向四周岩体扩展,爆破孔位置和底板煤岩交界面以及煤层内部的破坏较为严重,产生跨界面损伤裂纹。爆炸应力波从松软煤层底板岩层传播到松软煤层时,岩体和松软煤体的交界面产生透射压缩应力波和反射拉伸应力波,透射波作用于松软煤体,使煤层裂隙增加;反射波反作用于岩体,在煤岩交界面形成交叉裂纹,使底板岩层裂隙和松软煤层裂隙贯通,有利于松软煤层的瓦斯垂向运移流动和卸压瓦斯抽采。潘一东煤矿现场应用表明,煤层底板爆破增透后瓦斯抽采纯量及其浓度快速上升,抽采纯量从0.06 m^(3)/min提高到1.46 m^(3)/min,增加了23.33倍;瓦斯浓度从爆破前的10.46%上升到45.50%左右,增加了3.34倍,并且长时间维持在较高水平。研究成果可为深部松软煤层瓦斯高效抽采提供理论基础和技术支持。

低透气性煤层高压脉冲射流割缝-压裂增透技术应用研究

针对盘州平关镇大坪煤矿18采区20号煤层复杂地质条件及瓦斯抽采难题,提出一种高压脉冲射流割缝导向压裂增透技术。为验证该技术效果,分析了其增透技术机理,并设计了4种试验方案进行对比分析。结果表明,采用高压脉冲射流割缝导向压裂方案在瓦斯抽采效果方面显著优于其他方法,与普通抽采、高压脉冲射流割缝、高压水力压裂抽采瓦斯相比,其平均每日抽采瓦斯浓度分别提高了3.01倍、1.41倍和1.67倍;平均每日抽采瓦斯纯流量也相应提升了2.86倍、1.42倍和1.62倍。经过90 d的抽采,该方案的抽采影响半径达到了5.06 m,分别为普通抽采、高压脉冲射流割缝和高压水力压裂抽采方案的2.56倍、1.25倍和1.29倍;在抽采效果相同的条件下,钻孔施工时间分别比普通抽采、高压脉冲射流割缝和高压水力压裂方案缩短了60%、32%和20%,瓦斯抽采达标所需时间分别比普通抽采、高压脉冲射流割缝和高压水力压裂方案缩短了70%、50%和62%。高压脉冲射流割缝导向压裂技术对低透气性煤层瓦斯治理效果较为理想,可供类似矿井借鉴。

低透气煤层无泵式钻扩一体化增透技术与钻具研究

针对在低透气煤层常规机械掏穴、水力冲孔等增透施工中存在的施工效率低、掏穴装置稳定性差以及需要配备高压泵等问题,提出了无泵式钻扩一体化增透施工技术,研制了配套的双通道送水器、双通道钻杆和造穴装置,并进行了现场工业性试验。结果表明:钻扩一体化增透施工技术在煤矿井下静压水条件下,可实现一趟下钻完成先导孔和机械掏穴的同时作业,解决了常规掏穴装置刀翼开合不稳定、必须配套高压泵的问题,降低了该技术的使用成本;研发的双通道送水器、双通道钻杆和造穴装置工作灵活稳定且可靠性高,造穴段单孔直接扩大至原常规钻孔孔径的4.4倍,显著提升了瓦斯抽采效果,该技术的成功应用为煤矿井下低透气煤层瓦斯抽采钻孔施工提供了技术支撑。

松软煤层定向长钻孔钻进技术及应用

针对象山矿井3号煤层受采动影响,卸压瓦斯通过顶底板裂隙释放至保护层工作面及采空区,造成上隅角瓦斯浓度高的难题,结合突出矿井高应力软煤层等复杂地质条件,采用复合钻进与滑动定向钻进工艺,利用ZYL-6000D全方位千米钻机配套螺旋钻杆、YSX18矿用随钻测量系统,采用高压氮气钻进技术,在21315综采工作面施工定向长钻孔进行瓦斯抽采,抽采钻孔使用“三堵两注”两相封孔技术,最终形成松软煤层定向长钻孔钻进控制及钻探工艺技术。试验结果表明,ZYL-6000D全方位千米定向钻机配合高强度刻槽钻杆可提高钻进深度和效率,“三堵两注”两相封孔方法对钻孔周围裂隙进行有效封堵,瓦斯抽采浓度大幅度提升,实现松软煤层定向长钻孔瓦斯治理模块化抽采,为矿井安全高效稳定发展提供有力保障。

倾斜煤层群覆岩“三场”非对称特征及靶向抽采机制

倾斜煤层群“三场”(应力场、位移场和裂隙场)演化规律较为复杂,对卸压瓦斯运移和储集具有重要意义。为了探究倾斜煤层群“三场”演化规律,研究以新疆1930煤矿为对象,开展了倾斜煤层群多重采动相似模拟实验。分析了上覆岩层垮落形态,获得了覆岩应力演化特征,分析了覆岩位移分布和移动方向特征,阐明了采动裂隙分布特征。进而探究了三场演化规律对瓦斯运移的影响,并开展了定向钻孔瓦斯抽采现场试验进行验证。研究结果表明:倾斜煤层群多重采动下,采动裂隙矩形梯台呈现明显的非对称特征。低位侧覆岩应力变化较大,随开采次数增加,卸压效应更为明显,而高位侧覆岩应力变化较小;结合重力−倾角效应,高位侧覆岩更易破坏,垮落次序优先,呈非对称特征。覆岩位移分布呈非对称特征,高位侧位移显著且移动方向变化较大。高位侧裂隙区网格内采动裂隙频数明显高于低位侧;高位侧裂隙区破断裂隙分布更多,且开度较大;采动裂隙呈“高位扩展−低位压缩”的非对称特征。多重采动使得“三场”非对称特征更为显著。此外,覆岩贯通度存在“慢速减小−快速减小”的现象。基于“三场”演化特征和瓦斯运移的关系,揭示了瓦斯抽采靶向优选机制。结合试验结果,构建了基于“三场”演化规律的裂隙带瓦斯抽采靶点区判定流程。现场瓦斯抽采效果良好,保证了工作面安全高效回采。研究结果为倾斜煤层群卸压瓦斯精准抽采提供了理论参考,旨在提高倾斜煤层群瓦斯抽采量,防止上隅角瓦斯超限,实现倾斜煤层群安全高效开采。

高瓦斯矿井综合瓦斯抽采技术实施应用

为解决山西安泽玉华煤矿采煤工作面风排瓦斯量大的问题,实施应用了本煤层瓦斯抽采、采空区瓦斯抽采以及高位定向长钻孔裂隙带瓦斯抽采等综合瓦斯抽采技术,大大提高了瓦斯抽采效果,彻底解决了采煤工作面回风流瓦斯浓度偏高的问题,为矿井安全生产提供了安全保障,为高瓦斯矿井瓦斯治理提供了有益借鉴。