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%.

Coal seam drainage enhancement using borehole presplitting basting technology——A case study in Huainan

Xinji No. 2 underground coal mine extracts the coal seams #4 and #5. These two seams are highly gassy and gas drainage is required to control mine gas emission and reduce outburst risk. Because the seam permeability coefficient is very low and around 0.1 m^2/(MPa^2·d), a number of technologies have been trialled to enhance the seam permeability prior to gas drainage. Of these technologies trialled, the deep borehole presplitting blasting technology has been proven to be quite effective in increasing permeability. In Xinji No. 2 mine it doubled or sometimes tripled gas drainage volume. This paper describes the technology, its application in the enhancement of seam permeability in Xinji No. 2 coal mine, and its effect on gas drainage performance.

Gas drainage technology of high gas and thick coal seam

Gas drainage in Jincheng Mining Group Co.,Ltd.was introduced briefly and theimportance of gas drainage in gas control was analyzed.Combined with coal-bed gas occurrenceand gas emission,the double system of gas drainage was optimized and a progressivegas drainage model was experimented on.For guaranteed drainage,excavationand mining and realization of safety production and reasonable exploitation of gas in coalseams,many drainage methods were adopted to solve the gas problem of the workingface.

Gas Drainage Technology in Fully Mechanized Caving Face with Horizontal Sublevel Mining in Steep and Extra-Thick Coal Seam

This paper analyzes the gas source of the horizontally sectioned fully mechanized caving face in the steeply inclined and extra-thick seam of Adaohai Coal Mine, and numerically simulates the stress distribution and pressure relief of the lower section coal after the upper section working face is mined. It theoretically analyzed the reasonable layout of the drainage boreholes, and designed the drainage borehole layout accordingly. In the upper and lower section of the working face, the actual drainage effect of the boreholes was inspected, and the air exhaust gas volume in the working face was statistically analyzed. It was confirmed that the layout of boreholes was reasonable, the gas control effect of working face was greatly improved and fully met the needs of safe mining. The control effect was greatly improved and the need for safe mining was fully met, and thus a gas drainage technology suitable for the coal seam storage conditions and mining technology of the Adaohai Coal Mine was found. That is to say: the gas emission from the working face of the section mining mainly comes from its lower coal body. Pre-draining the lower coal body of the section and depressurizing gas interception and drainage are the key to effectively solve the problem of gas emission from the working face. Drainage boreholes in the working face of the section should be arranged at high and low positions. The high-level boreholes are located about 2 m from the top of the working face, and the high-level boreholes are about 9 m away from the top of the working face. Through the pre drainage of high and low-level boreholes in advance and the interception and pressure relief drainage, the gas control in the horizontal sublevel fully mechanized caving mining face in steep and extra thick coal seam can realize a virtuous cycle.

Regional gas drainage techniques in Chinese coal mines

China's rapid economic development has increased the demand for coal.These results in Chinese coal mines being extended to deeper levels.The eastern Chinese,more economical developed,regions have a long history of coal mining and many coal mines have now started deep mining at a depth from 800 to 1500 m.This increase in mining depth,geostresses,pressures,and gas content of the coal seam complicates geologic construction conditions.Lower permeability and softer coal contribute to increasing numbers of coal and gas outburst,and gas explosion,disasters.A search on effective methods of preventing gas disasters has been provided funds from the Chinese government since 1998.The National Engineering Research Center of Coal Gas Control and the Huainan and Huaibei Mining Group have conducted theoretical and experimental research on a regional gas extraction technology.The results included two important findings.First,grouped coal seams allow adoption of a method where a first,key protective layer is mined to protect upper and lower coal seams by increasing permeability from 400 to 3000 times.Desorption of gas and gas extraction in the protected coal seam of up to 60%,or more,may be achieved in this way.Second,a single seam may be protected by using a dense network of extraction boreholes consisting of cross and along-bed holes.Combined with this is increased use of water that increases extraction of coal seam gas by up to 50%.Engineering practice showed that regional gas drainage technology eliminates regional coal and gas outburst and also enables mining under low gas conditions.These research results have been adopted into the national safety codes of production technology.This paper systematically introduces the principles of the technology,the engineering methods and techniques,and the parameters of regional gas drainage.Engineering applications are discussed.

东曲矿预留钻孔疏放28206工作面老空积水技术研究

近距离煤层群开采时,上部煤层开采后形成的采空区积水是威胁下部煤层安全开采的主要因素之一。针对传统采空区积水的防治方法存在一定盲目性,导致工程量通常较大的情况,本文根据东曲矿28206工作面和29206工作面是近距离煤层开采的具体情况,提出在28206工作面开采时预留疏水钻孔,对工作面低洼区域采空区积水进行监测和有序疏放,最终保证了下部29206工作面的安全开采,为类似近距离煤层群防治采空区积水提供了经验借鉴。

瓦斯抽放孔“一孔两用”注水降尘技术研究

为了解决潞安集团郭庄煤业3308工作面粉尘浓度高的问题,基于煤层注水降尘技术,开展工作面瓦斯抽采孔进行动静压联合注水降尘实验研究。实验结果表明,煤层注水过程中,距离钻孔越近增水量越大,平均增水率为55.6%,煤层注水前后粉尘质量浓度最大降幅可达78%,“一孔两用”钻孔布置以及注水方式能够减少煤层注水二次打孔周期及投资,取得一定的经济效益。

松软煤层近水平孔解卡机理研究

为了减少松软煤层卡钻事故的发生,分析了近水平孔卡钻的原因及卡钻的形成过程,并建立了各阶段的卡钻力学模型。通过对卡钻主要影响因素的分析,得出解卡的关键在于减小岩屑堆积的密实度和提升排渣效率,以此指导了L型螺旋槽钻杆的结构及功能设计。通过对U型槽螺旋钻杆、三棱钻杆和L型螺旋槽钻杆的排渣性能进行试验对比,验证了L型螺旋槽钻杆的排渣性能最优。通过现场试验验证了L型螺旋槽钻杆较市场上常用的U型槽螺旋槽钻杆更优。

底板钻孔截流抽采技术在分叉煤层瓦斯治理中的应用

针对突出煤层分叉区域工作面开采过程中2下煤层卸压瓦斯大量涌出、上隅角瓦斯治理困难等问题,采取在上顺槽施工底板定向长钻孔、下顺槽施工拦截钻孔截流抽采相结合瓦斯治理技术,研究底板拦截钻孔布孔方式、层位及抽采范围,显著提高拦截钻孔的成孔率和抽采效果,实现了瓦斯零超限。

东欢坨矿-950 m水平石门揭煤瓦斯基础参数测试及抽采实践

东欢坨矿延深至-950 m水平后,煤层瓦斯含量、压力逐步增大,瓦斯灾害风险较大。为了解决新水平石门揭煤安全问题,自主设计研发上仰瓦斯压力测试钻孔补偿式不泄压装置和高压注浆二次封堵工艺,创新性地解决了测压过程遇到的封孔以及承压水干扰的问题,合理设计瓦斯综合治理方案,安全高效的完成了新水平石门揭煤工作,为矿井后续其他煤层的揭煤和瓦斯治理奠定了坚实的理论和实践基础。

液态CO_2相变致裂煤层增透技术布孔方式研究

液态CO2相变致裂技术是一种新颖的低透煤层增透技术。为了更好地将液态CO2相变致裂技术运用到低透气煤层增透领域中,在平煤十三矿进行了液态CO2相变致裂的穿层强化预抽煤层瓦斯现场试验,通过煤层致裂后的瓦斯抽采效果反映出的不同布孔方式下的致裂差异,确定液态CO2的爆破孔的合理布孔方式。现场试验表明液态CO2相变致裂在交错的梅花孔布置方式下由于能量分布均匀,致裂效果优于矩形孔布置方式,研究结果为该技术在煤层增透强化预抽领域的推广应用奠定了基础。

松软煤层“护孔卸压”钻进力学机制

为解决常规套管钻具应用软煤层钻进存在着钻进阻力大、效率低的技术难题,提出“护孔卸压”钻进新观点,建立护孔钻进旋转阻力矩模型、轴向阻力模型及护孔数值模型,分析常规套管钻具应用于软煤层钻进存在的技术缺陷,探讨“护孔卸压”钻进工艺方法实现卸压、降阻的力学机制。结果表明:受软弱煤岩层钻孔收缩产生的围压影响,应用常规套管钻具钻进,在较短的钻孔深度范围内其旋转阻力矩和轴向阻力超过了钻机的额定扭矩及提拔力,钻杆将无法旋转及退钻,致使钻进终止;通过在套管钻具表面设置间隙或孔结构,减小护孔钻杆与钻孔壁的接触面积,为钻孔孔壁留设变形空间,钻杆表面形成的“卸压区”释放了钻杆周围煤体膨胀应力,并且旋转的钻杆不断切除膨胀的煤体,降低了软煤钻孔膨胀变形对钻杆产生的摩擦阻力;提出护孔面积比Sk概念,用来表征钻杆表面孔隙留设面积大小,伴随Sk减小,其旋转阻力矩和轴向钻进阻力呈逐渐降低趋势,降低幅度可达50%以上,从而降低了钻机的动力损耗,有效提高松软煤层的钻孔深度。基于“护孔卸压”原理,构建了螺旋护孔钻杆模型和多孔结构护孔钻杆模型,在实际应用中,结合施工地点的煤岩力学参数,合理确定护孔面积比Sk是护孔卸压钻具结构优化设计的关键。

多级破煤水力冲孔强化松软低透煤层瓦斯抽采技术研究

在松软低透煤层中应用水力冲孔强化瓦斯抽采时,经常出现堵孔、卡钻等现象。针对这一问题,提出多级破煤水力冲孔技术。在分析堵孔发生原因的基础上,研制了多级破煤系统装置：一级破煤装置对原始煤体进行初始破碎;二级破煤装置对包裹在钻头及钻杆周边的煤渣、煤泥进行破碎、清除;三级破煤装置对小块煤体再次研磨。基于淹没射流速度场分布特征,分析了二级破煤装置射流轴向流速衰减规律,确定了二级破煤装置与一级破煤装置的最佳距离。在此基础上研发了多级破煤水力冲孔工艺,并应用于鹤煤八矿-655轨道石门揭煤瓦斯预抽,应用结果表明采用多级破煤水力冲孔工艺能够实现排渣顺畅,避免堵孔等现象的发生,单孔出煤量为3-8吨,冲孔后瓦斯抽采浓度及抽采流量均提高了3~15倍,石门预抽达标时间缩短至三个月以内,为安全快速揭煤提供了良好基础。

穿煤层钻孔定向水压致裂的数值仿真

选取鸡西城山煤矿现场实例,利用RFPA2D-Flow软件模拟了穿煤层钻孔定向水压致裂全过程.分析了应力、水压的分布与变化规律,研究了损伤区域、卸压区域的形成与扩展过程.对穿煤层钻孔定向水压致裂前后煤层瓦斯抽放过程中瓦斯抽放效果及压力分布进行了对比研究.结果表明,实施定向水压致裂后压裂孔与控制孔之间的卸压区成为主要的瓦斯渗流通道,使瓦斯抽放效果显著提高.

大径孔预抽煤巷条带瓦斯技术的优化及应用

针对孟津煤矿二2煤层弱突出危险性的特点,以及11031工作面胶带、轨道顺槽掘进速度缓慢的问题,研究不同孔径钻孔的卸压范围和抽放效果。采用大直径钻孔,钻孔分区式布置对现有区域消突技术进行优化,孔径113 mm的抽放钻孔单孔抽放瓦斯纯量为孔径94 mm的1.8倍。表明大径顺层长钻孔的应用,能够有效消除煤巷预抽条带瓦斯突出危险,提高掘进速度,确保掘进工作面的安全生产。

低透气性突出煤层巷道快速掘进的试验研究

针对在低透气性突出煤层巷道掘进过程中，煤与瓦斯突出综合检测指标经常超限，掘进速度缓慢等问题，提出了深孔预裂控制爆破和巷帮钻孔边抽边掘相结合的综合防突技术，研究了深孔预裂控制爆破技术的作用机理，阐述了深孔预裂控制爆破技术的工艺流程和巷帮钻孔的布置参数．研究表明：在低透气性突出煤层中采用深孔预裂控制爆破和巷帮钻孔边抽边掘相结合的防突措施，可有效地消除激发突出的应力和煤体结构的不均匀性，提高煤体强度和煤层透气性，使巷帮钻孔瓦斯抽放量大幅度地提高，增大了煤体抑制突出的阻力，能有效地预防和消除在掘进过程中煤与瓦斯突出的危险性，且提高巷道掘进速度3～4倍．

A-B胶封孔工艺在煤矿顺层抽采钻孔中的应用性试验

针对目前煤矿常用的钻孔封孔工艺技术存在的不足,提出了A-B胶封孔工艺,并在松藻煤电公司打通一矿W2704顺层钻孔进行了封孔试验,结果表明,该工艺不仅操作简单、方便、节约成本,而且还可提高钻孔瓦斯抽采浓度。采用A-B胶封孔工艺后,钻孔抽采瓦斯的平均浓度为42.4%～60.2%,相比采用马丽散F封孔提高了12.2%～24.5%。

双孔聚能爆破煤层裂隙扩展贯通机理

针对双孔聚能爆破孔间煤层裂隙扩展贯通问题,基于对双孔爆破应力波叠加效应的分析,建立双孔聚能爆破数值分析模型,研究双孔同时起爆时应力波的传播特征、煤体的应力状态、煤体裂隙扩展贯通规律以及应力波叠加效应对裂隙扩展的影响.结果表明,应力波叠加效应致使两爆破孔中间截面上部分区域及其邻域内形成均压区,迫使部分径向裂隙转向,主导爆生裂隙空白带的形成;两爆破孔间的定向裂隙相互贯通后,爆生气体相互作用促进贯通区裂隙的扩展并贯穿空白带.同时,结合煤层深孔聚能爆破现场试验发现,在两爆破孔外侧,应力波叠加效应促进裂隙的扩展,该作用随着远离爆破孔呈先增加后减小之势;在两爆破孔之间,应力波叠加效应抑制部分区域裂隙的扩展,致使两爆破孔之间不同位置处煤层增透效果有起伏变化.

卸压爆破在低透气突出煤层快速掘进中的应用

针对在高瓦斯低透气突出煤层巷道掘进过程中,瓦斯频繁超限、突出预测指标超标次数多、防突措施的钻孔工程量大、巷道掘进缓慢等问题,提出了用深孔控制爆破来释放煤体所积聚的弹性能,以扩大工作面前方煤体卸压带的范围,结合巷帮钻孔边抽边掘的措施,达到增透卸压强化抽放快速消突的目的,实现巷道安全快速掘进。

煤层钻孔升温提高瓦斯抽放效率的新思路

为了进一步提高煤体瓦斯防治效果,基于我国煤储层高瓦斯、低渗透等特性,结合现有的绿色环保蓄热技术及材料,提出了一种新的煤层钻孔加热方法。主要是通过拟定设计一种适用于煤层钻孔的相变储热材料封装装置,并在装置内装入选定的相变储热材料,根据材料的相关参数进行模拟计算热响应半径及其对瓦斯解吸的影响规律。结果显示单从计算角度看,利用在钻孔内安放相变材料提高煤层温度促解吸方法具有一定的可实施性,且相比常规的负压瓦斯抽放、注气增产等方法更节能环保,具有一定的优越性。