Pressure relief, gas drainage and deformation effects on an overlying coal seam induced by drilling an extra-thin protective coal seam

Numerical simulations and field tests were used to investigate the changes in ground stress and deformation of, and gas flow from, a protected coal seam under which an extra-thin coal seam was drilled. The geological conditions were: 0.5 meter mining height, 18.5 meter coal seam spacing and a hard limestone/fine sandstone inter-stratum. For these conditions we conclude: 1) the overlying coal-rock mass bends and sinks without the appearance of a caving zone, and 2) the protected coal seam is in the bending zone and undergoes expansion deformation in the stress-relaxed area. The deformation was 12 mm and the relative defor- mation was 0.15%. As mining proceeds, deformation in the protected layer begins as compression, then becomes a rapid expansion and, finally, reaches a stable value. A large number of bed separation crannies are created in the stress-relaxed area and the permeability coefficient of the coal seam was increased 403 fold. Grid penetration boreholes were evenly drilled toward the protected coal seam to affect pressure relief and gas drainage. This made the gas pressure decrease from 0.75 to 0.15 MPa, the gas content decrease from 13 to 4.66 m3/t and the gas drainage reach 64%.

Three-dimensional numerical simulation of methane drainage by high-level drill holes in a lower protective coal seam with a “U” type face

Different drill-hole positions may produce different drainage results in low protective coal seams.To investigate this possibility,a 3D stope model is established,which covers three kinds of drill holes.The FLUENT computational fluid mechanics software is used to solve the mass,momentum and species conservation equations of the model.The spatial distributions of oxygen and methane was obtained by calculations and the drainage results of different drill-hole positions were compared.The results show that,from top to bottom,methane dilution by oxygen weakens gradually from the intake to the return side,and methane tends to float;methane and oxygen distribute horizontally.The high-level crossing holes contribute to better methane drainage and a greater level of control.Around these holes,the methane density decreases dramatically and a "half circle"distribution is formed.The methane density decreases on the whole,but a proportion of the methane moves back to deep into the goaf.The research findings provide theoretical grounds for methane drainage.

Effect of protective coal seam mining and gas extraction on gas transport in a coal seam

A gas–solid coupling model involving coal seam deformation,gas diffusion and seepage,gas adsorption and desorption was built to study the gas transport rule under the effect of protective coal seam mining.The research results indicate:(1) The depressurization effect changes the stress state of an overlying coal seam and causes its permeability to increase,thus gas in the protected coal seam will be desorbed and transported under the effect of a gas pressure gradient,which will cause a decrease in gas pressure.(2) Gas pressure can be further decreased by setting out gas extraction boreholes in the overlying coal seam,which can effectively reduce the coal and gas outburst risk.The research is of important engineering significance for studying the gas transport rule in protected coal seam and providing important reference for controlling coal and gas outbursts in deep mining in China.

Study on the countermeasures against methane outburst of mining multiple upper protective layers in coal seams cluster

In order to prevent coal and methane outbursts, mining protective layers is an effective means, yet no precedents of mining multiple protective layers is discoveried in seams which includes several seams are prone to outburst like Xinzhuangzi Mine. This paper perfected the related theories through analyzing mining multiple upper protective layers. By means of examining several parameters, it synthetically analyzed and ascer- tains the protected effectiveness and scope and reasonable parameters, finally obtained the specific indexes and effectiveness of mining multiple protective layers in coal seams cluster.

Top coal caving mining technique in thick coal seam beneath the earth dam

It is important to study the mining technology under structures for raising the coal resources recovery ratio. Based on the geological and mining conditions, the top coal caving harmonic mining technique in thick coal seam beneath the earth dam was put forward and studied. The 5 factors such as the panel mining direction, panel size, panel location, panel mining sequence and panel advance velocity were taken into account in this technique. The dam movement and deformation were predicted after the thick coal seam mining and the effects of mining on the dam were studied. By setting up the surveying stations on the dam, the movement and deformation of the dam were observed during mining. By taking some protective measures on the dam, the top coal caving mining technique in thick coal seam beneath the earth dam was carried out successfully. The study demonstrates that harmonic mining in thick coal seam is feasible under the dam. The safety of the earth dam after mining was ensured and the coal resources recovery ratio was improved.

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。

以煤层倾向为参考方向的锐角优化垂线法煤柱设计方法

垂线法广泛应用于我国矿区地表建(构)筑物的保护煤柱的设计,但其原理中存在走向方向不明确导致计算时需人工干预和小角值拐角处保护煤柱过估等问题。针对村庄尺度的建筑物群,提出应按位置给出不同的开采参数和松散层参数;用煤层倾向作为垂线法的参考方向,代替指向不明确的走向,实现垂线计算公式选择、垂线长度计算的自动化;提出锐角优化算法,解决煤柱角点角值较小时出现的煤柱留设尺寸过大问题。基于上述优化,通过MATLAB编程实现煤柱自动化计算,并一定程度上减小了煤柱的尺寸。优化后的垂线法能够更好地应用于矿山保护煤柱设计。

深煤层气井低伤害完井液分析

深煤层气井的开采通常是采用水敏损害的完井液,但这类完井液存在着严重的伤害问题,对煤层气井的开采效率有着不利影响。在煤层气开采过程中,需要不断向井底注入液体,在注入过程中不可避免地会对煤层造成一定的伤害。从深煤层气井开采过程中出现的问题出发,对煤层气井中常见的完井液进行了分析和讨论,并在此基础上提出了相应的低伤害完井液方案。分析结果表明:低伤害完井液能有效降低深井煤层气开采过程中出现的问题。

我国煤层水害基本架构及发展情势

为了解决煤炭资源安全高效开发过程中面临的煤层水害问题,基于近20余年间煤层水害事故的统汇分析,提出了“隐蔽突水致灾因素”萌生、煤层水害“三要素”定型、多要素耦合孕灾、突破临界状态激发灾变和灾变后负效应显现等5个煤层水害的主体构成阶段,依据各阶段独立属性特征,将煤层水害概括为顶板水害、底板水害和老空水害3个主类,以及巨厚基岩含水层高势能涌(淋)水、岩溶陷落柱导升突水、同位水平空间侧向涌水等11个子类,并对不同类型煤层水害的孕灾致灾诱因、发育发展过程机理、灾变显现特征等进行阐述。最后,对我国煤层水害的未来发展情势做了简要展望和分析。

近直立煤层上覆煤柱下巷道冲击地压防治研究

以近直立特厚煤层终采线保护煤柱下掘进过程中遇到冲击地压问题为工程背景,通过数值模拟、理论分析和现场实践的方法,研究了保护煤柱下方掘进面开采过程中冲击危险程度的变化,提出了相应的防治手段和检验措施,得出如下结论:巷道掘进影响了煤柱区域应力状态,增加终采线煤柱区域应力集中区的范围及冲击危险性;掘进工作面经过煤柱边缘应力集中区时,前方应力峰值较大,围岩冲击危险性较高。根据PDCA管理模式提出了理论分析→实施解危→效果验证→掘进实践→优化调整→效果验证的双循模式管控,通过实施掘进面密集大孔径卸压孔和全方位高压注水软化等系统性防治工程,并采用微震、地音、电磁辐射等技术进行效果验证,实现了掘进工作面安全的通过煤柱影响区域。这为矿井冲击地压防治提供了参考和借鉴。

上保护层双工作面开采卸压增透效应研究

针对中兴煤业2#煤层煤与瓦斯突出、被保护层工作面长度大、抽采能力有限等问题,提出了上保护层双工作面开采方式。通过理论计算、数值模拟和现场实测相结合的方法,研究了采用该方式时被保护层工作面的垂直应力和垂直位移的分布规律,分析了2#煤层的卸压效果。结果表明:随保护层工作面长度的增大,卸压比例总体呈减小的趋势,当保护层工作面长度为110 m时,被保护层工作面的垂直应力和垂直位移的卸压比例分别达到91%和87.4%。卸压后现场实测2^(#)煤层最大残余瓦斯含量和最大残余瓦斯压力分别降低为5.37 m^(3)/t和0.44 MPa,孔隙率增加到4.05%,煤层透气性系数增加到1.08 m^(2)/(MPa^(2)·d),最大膨胀变形量大于3‰,各指标均表明卸压增透效果显著。

上保护层开采下特厚突出煤层沿空巷道合理位置研究

基于上保护层开采下特厚煤层瓦斯地质条件,综合理论分析、数值模拟、工程实践等方法,对采空区侧向应力分布特征、突出危险性预测指标变化规律及沿空巷道合理位置进行了研究。结果表明:上保护层开采后裂隙岩体存在应力恢复效应,应力恢复后采空区侧向应力峰值会向采空区方向移进;根据采空区侧向不同距离下的煤体突出预测指标测试结果划分了充分卸压排放区、有效卸压排放区及危险区域,结合工程类比、数值模拟结果、隔绝采空区气体需要,确定了沿空煤柱留设宽度为5~7 m;调整后巷道掘进期间突出预测指标及回风瓦斯浓度最大值分别为0.16 mL/(g·min^(1/2))、0.22%,与未调整之前相比降幅分别达到66%、35.3%,保证了巷道安全掘进,验证了沿空煤柱留设的合理性。

煤层群上下保护层开采围岩应力及裂隙演化规律研究

为实现煤层群上下保护层开采过程中被保护层卸压瓦斯的高效抽采,采用数值模拟方法研究上下保护层开采后围岩应力、裂隙分布及演化规律,探明上下保护层开采的卸压瓦斯富集区。研究结果表明:下保护层开采后,被保护层工作面上侧覆岩卸压高度明显大于下侧覆岩卸压高度,次采上保护层后,增大了被保护层卸压范围。下保护层开采后被保护层走向卸压角为63°,倾斜上下边界卸压角为87°、72°。上保护层开采后被保护层走向卸压角为59°,倾斜上下边界卸压角为76°、79°。经过保护层卸压后,被保护层抽采卸压瓦斯纯流量相比卸压前呈现10余倍增大,卸压瓦斯抽采具有明显的时空效应。

保护层开采与卸压瓦斯协同抽采技术研究与应用

针对深部低透突出煤层群下保护层开采后上覆被保护层卸压瓦斯及下保护层瓦斯协同抽采的难题,新景矿采用“地面井预抽+高(低)位抽采巷”实现了被保护层卸压瓦斯及上隅角瓦斯的协同抽采。综合应用机械造穴、地面井压裂等增透措施,提高了新景矿15号煤层抽采效率。增透前后支管抽采瓦斯纯流量提高了2.27倍,缩短了保护层工作面预抽瓦斯的达标时间;通过对比15号煤层开采前后3号、8号及9号被保护层的卸压瓦斯地面井抽采瓦斯纯流量提高了1.85倍,实现了保护层与被保护层瓦斯的协同抽采,开采突出煤层群做到安全可控,对阳泉矿区煤层群安全高效开采具有重要的参考意义。

精准定向水力冲孔高效卸压抽采技术应用

针对松软煤层瓦斯抽采钻孔出现钻孔成孔率低和抽采效果差的问题,提出了精准定向水力冲孔高效卸压抽采技术,并基于现有钻机平台研发了配套的定向保直装置和钻冲护一体装置,能够一次实现定向钻进、水力冲孔卸压和全孔段下放筛管功能。现场试验得出:对比矿井原有技术平均每百米偏斜减小了60.46%,钻孔瓦斯抽采纯量平均值提高了4.72倍,瓦斯抽采衰减系数降低了27.5%。该技术在钻孔偏斜率,施工效率,筛管下放率,降低瓦斯衰减等方面皆优于矿井原有技术,简化施工工艺,提高钻孔成孔率,改善了软煤钻孔的瓦斯抽采效果,保障矿井安全高效生产。

采煤工作面煤柱自燃发火防治技术研究

11302综采工作面回采的11#煤层为自燃发火煤层,采面回风巷护巷煤柱在邻近采面回采扰动、地质构造等多因素影响下内部裂隙发育,导致煤柱局部出现温度升高等自燃发火迹象。为确保11302综采工作面安全回采并解决回风巷煤柱自燃发火问题,提出综合采用煤柱注浆+煤壁喷浆方式进行防灭火,通过煤柱注浆封堵内部漏风裂隙、煤壁喷浆隔绝煤柱与空气接触并封堵表面裂隙,并对注浆及喷浆方案进行详细分析。工程应用后,11302回风巷煤柱局部高温点温度降至正常温度,且采面后续回采期间煤柱内温度均未再出现升温情况,表明现场采用的煤柱自燃发火防治技术取得较好效果。

保护层开采工作面瓦斯综合治理技术研究

针对矿井回采煤层瓦斯含量高、压力大等问题,提出先回采下覆厚度较薄、瓦斯治理难度相对较低的6号煤层。将6号煤层作为保护层开采,从而消除下覆9号煤层、上覆2号及5号煤层的突出危险性。针对6号煤层10601工作面回采期间上邻近层、下邻近层以及采空区瓦斯涌出量大等问题,提出综合采用高位钻孔、高抽巷、采空区埋管、强化本煤层抽采等方式进行治理。现场应用后,10601工作面回采期间回风隅角、回风流瓦斯浓度分别控制在0.43%、0.32%以内,采面瓦斯涌出量大问题得以较好解决。

特厚煤层动压巷道小煤柱护巷技术应用

以A特厚煤层煤矿39204工作面为例,介绍一种适用于特厚煤层动压巷道的小煤柱护巷技术。采用FLAC3D数值模拟软件对特厚煤层动压巷道围岩应力分布及变形情况进行仿真分析,结合小煤柱动压巷道控制理论,设计了特厚煤层小煤柱动压巷道控制方案,并将该方案应用于A特厚煤层煤矿工程实践,确认所提出的特厚煤层动压巷道小煤柱护巷技术具有较强的可行性。

煤层气开发老区L型加密水平井钻井及排采技术研究

煤层气开发老区L型加密水平井的技术方案,即通过在低产井的井间添加加密水平井,建立起单井之间的有效井间干扰,使整个区域实现整体降压,从而达到提高低产井单井产气量的目的。本文通过从布井、储层保护、钻井及排采四个方面分别提出了老区加密井在具体实施过程中需要注意事项,为煤层气开发老区加密井钻井及排采提供了一个系统的可行的技术方案。

急倾斜煤层群保护层开采条件下采场应力演化规律

急倾斜煤层群开采存在复杂的岩层运移过程并易导致强矿压事故的发生。为保障兴安煤矿煤层群的安全开采,采用保护层开采技术对主采煤层进行卸压优化,依托FLAC^(3D)数值模拟软件建立急倾斜煤层开采数值模型,探究保护层开采条件下的采场应力、位移与被保护煤层应力、位移的分布演化规律,利用理论计算方法分析了有效卸压保护范围,验证保护层开采技术的可靠性。研究结果表明:急倾斜煤层保护层开采条件下会出现位移与应力扩展的不共轴现象;保护层推进过程中,采场应力与位移演化呈现出初始增长、快速增长、逐渐稳定的3阶段演化规律;保护层开采的有效卸压范围超过80%。