Gas outburst disasters and the mining technology of key protective seam in coal seam group in the Huainan coalfield

Coal and gas outburst disasters in coal seams are becoming more serious as coal mines extend deeper underground in China. To aid gas control in high-gas outburst coal seam group, this study performed research based on the geological conditions of the Xinzhuangzi coal mine in the Huainan coalfield. The laws of gas occurrence, the strength of the coal outburst, and the regional partition were studied. Simultaneously, we introduced the key protective seam mining technology and confirmed the mining sequence of coal seam groups. The results indicate that (1) each seam absorbs gas well, and the currently measured gas content is up to 15.0 m³/t. (2) Although some differences about coal seams outburst intensity remain, the differences in the same group are very small. (3) The coal seam B10 was chosen as the key protective seam and was mined first; then adjacent seams were mined from bottom to top by layer within the roof of B10 and from top-to-bottom within the floor of B10 to guarantee each adjacent coal seam received the good effects of pressure-relief and increasing permeability. (4) The main methods of gas extraction in each protected seam are surface boreholes and net-like penetrating boreholes in the floor roadway, and related technical parameters were determined according to the degree of pressure-relief in coal seam. This in situ experiment indicates a method aiding the gas control problem and guaranteeing safe and highly efficient exploitation of high-gas outburst seams.     

Stress distribution characteristic analysis and control of coal and gas outburst disaster in a pressure-relief boundary area in protective layer mining

Coal and gas outburst disasters in coal seams are becoming more serious as coal mines extend deeper underground in China. Furthermore, the protective coal seam mining technology featured by economic efficiency has been proven to be the most effective and widely applied method for the prevention of coal and gas outburst disasters. However, the determinations of the protective area coal and gas outburst prevention in a pressure-relief boundary area are fundamental issues that research should be focused on. The technical method for determining stress distribution in pressure-relief boundary area during protective coal seam mining is put forward in this paper. The method is based on a stress-seepage coupled relationship within a gas-containing coal seam. The method includes complex lab experiments and on-site measurements at the Qingdong Coal Mine. The final data illustrate that the permeability and vertical stress in the pressure-relief boundary area of the coal sample form a negative exponential function relationship. Additionally, the permeability of the coal sample within the abovementioned area is significantly different compared with that located at the center of the pressure-relief area. In the pressure-relief boundary area, the gas pressure distribution gradient is 0.0375 MPa/m, while the vertical stress distribution gradient registers 0.56 MPa/m. Under this condition, coal and gas outburst disasters are prone to be triggered. Therefore, effective precautions against coal and gas outburst disasters can be put forward in accordance with stress distribution characteristics within the abovementioned “boundary area.”     

韩城矿区碎软煤层顶板梳状孔水力压裂瓦斯抽采工程实践

韩城矿区碎软煤层发育,煤层透气性差,本煤层钻孔钻进困难,瓦斯抽采效果差。顶板梳状孔水力压裂技术结合了水力压裂技术和定向钻进技术二者的优势,是解决碎软低渗煤层瓦斯抽采难题的有效技术途径。在韩城矿区王峰煤矿3号煤层顶板粉砂岩中施工长钻孔并向煤层开分支,采用套管+封隔器座封的整体压裂方式进行水力压裂工程试验。钻孔总长度344 m,有效压裂长度284 m,累计注水量874.79 m3,最大泵注压力9.4 MPa。试验结束后对钻孔瓦斯抽采相关参数连续监测86 d,钻孔瓦斯抽采体积分数27%~51%,平均42.11%,钻孔瓦斯抽采纯量8.25~21.41 m3/min,平均17.02 m3/min,钻孔累计抽采瓦斯量约210万m3。与常规的穿层钻孔水力冲孔技术相比,该技术百米钻孔瓦斯抽采量提高了11.48倍,初步证明了该技术在碎软煤层瓦斯强化抽采领域的适用性。      

深部强冲击地压易发矿区厚煤层开采解放层卸压效果数值模拟

为研究深部强冲击厚煤层开采上、下解放层的卸压效果。采用数值模拟方法,分析不开采解放层,开采下解放层,开采上、下解放层条件下,被解放层的应力变化情况及应力变化规律,计算开采下解放层后的合理卸压角,确定解放层平巷位置。模拟结果表明开采上、下解放层后,应力明显减小,但仍存在高应力区,易发生冲击地压,必要条件下应采用其它辅助卸压方式。证明了煤壁前方应力增加区域一般在煤壁前方8～25m。该研究为工作面开采设计提供理论指导,对防治冲击地压具有一定的现实意义。     

底板梳状长钻孔替代穿层钻孔瓦斯抽采技术可行性

底板岩巷穿层钻孔抽采技术和本煤层定向长钻孔抽采技术是目前高瓦斯和突出矿井回采工作面最为主要的瓦斯治理措施。晋城矿区赵庄矿煤层具松软低透气性特点,主要采用岩巷穿层钻孔消突为主,本煤层顺层钻孔消突为辅的瓦斯治理方法。但底板岩巷穿层钻孔存在工程量大、施工周期长及成本高等缺点,本煤层钻孔存在钻孔抽采不均匀、钻孔覆盖密度不足等技术缺陷。为对比考察底板梳状长钻孔与底板岩巷穿层钻孔的抽采效果,在赵庄矿1307采面开展了2种瓦斯治理方法。结果表明:抽采条件和抽采范围相同条件下,5个底板梳状长钻孔的瓦斯抽采总量占到底板岩巷穿层钻孔瓦斯抽采总量的75.4%,而底板梳状长钻孔的经济投入仅占底板岩巷穿层钻孔经济投入的29.2%。由此得出,研究区梳状长钻孔替代穿层钻孔的瓦斯抽采技术是可行的。该研究为底板梳状长钻孔替代底板岩巷的技术可行性提供了实践参考,为松软低透的高瓦斯和突出矿井的瓦斯治理提供了更为经济可行的治理方案。      

中硬低渗煤层定向长钻孔水力压裂瓦斯高效抽采技术与应用

针对黄陇侏罗纪煤田中硬煤层渗透性差、瓦斯抽采浓度及流量衰减速度快等问题,利用自主研发的水力压裂成套工艺设备,提出煤层定向长钻孔水力压裂瓦斯高效抽采技术,并在黄陇煤田黄陵二号煤矿进行工程应用试验。现场共完成5个定向长钻孔钻探施工,单孔孔深240~285 m,总进尺1 320 m;采用整体压裂工艺对5个本煤层钻孔进行压裂施工,累计压裂液用量1 557.5 m3,单孔最大泵注压力19 MPa;压裂后单孔瓦斯抽采浓度及百米抽采纯量分别提升0.7~20.5倍、1.7~9.8倍;相比于普通钻孔,压裂孔瓦斯初始涌出强度提升2.1倍,钻孔瓦斯流量衰减系数降低39.6%。试验结果表明:采取水力压裂增透措施后,瓦斯抽采效果得到显著提升,煤层瓦斯可抽采性增加,为类似矿区低渗煤层瓦斯高效抽采提供了技术支撑。      

Pressure-Relief Mining of the Working Face Under the Coal Pillar in the Close Distance Coal Seams

Intensive strata behaviors are generated when the No. 8707 working face of the 8# coal seam in a coal mine is advanced by way of the pillars left over of the upper part of 7# close distance coal seam. The theoretical analysis, numerical simulation and filed measurement were utilized to obtain the rule of the stress change when the 8707 working face of the 8# coal seam passes the pillars left over of the 7# coal seam. Meanwhile, a pressure-relief mining (PRM) technology was put forward. According to the research results, when the 8707 working face in the 8# coal seam was advanced to the position that was 20 m in front of the pillar left over, the abutment pressure reached the maximum for 26 MPa and the stress concentration factor was 3.25, which was likely to give rise to the rock burst. With the advance of the working face, the abutment pressure was reduced slowly. As the 8707 working face advanced 15 m away the pillar left over, the transfixed shear failure region of 45° was found in the bedrocks of the upper and lower coal seams, which was readily to give rise to the shear rupture, leading to the rock burst. Based on the aforementioned research, this research carried out the PRM by applying the hydraulic fracturing technology on the coal roof and pillar, which can ensure the safety and efficient mining of working faces.     

An experimental and numerical investigation on the deformation of overlying coal seams above double-seam extraction for controlling coal mine methane emissions

This study investigates the deformation and the resultant pressure relief of highly gassy coal seams where a double seam mining operation takes place at lower depths at the Wulan Coal Mine, China. In order to predict the depressurization effect in the overlying coal seams, we simulate the extraction process by constructing a scaled model in the laboratory using similar rock materials. Analyses of experimental results concluded that due to the mining-induced stress redistribution, the pressure within target coal seams, which were 109 m above the mined seams, could be fully relieved to attain the statutory approval for gas drainage.In addition to scaled-model studies, computational modeling studies were conducted using UDEC (Universal Distinct Element Code), which showed that the features of deformation resulting from the double-seam extraction were different from that of in the case of single-seam extraction. The results of the numerical studies revealed that in addition to the panel margin on the air return side, areas near the intake entry could also be considered as borehole drilling positions. Besides, it was found that the gob of the extracted seams below the gassy one provided a “buffering effect” for the would-mined protective coal seam and that the depressurization effect was largely weakened.The laboratorial findings are instructive to the field practice of methane drainage. During the mining operation, a “displacement comparison method” was adopted to measure the dilated amount of protected coal seams, and as expected, the maximum dilation percentage was much more than 0.2% — the critical value upon which the target coal seam is appropriately depressurized to allow gas drainage to be safely and effectively implemented.     

下伏煤层瓦斯压力消散数值模拟

平煤五矿己15煤层为低瓦斯煤层,下伏己16-17煤层为高瓦斯煤层,相对层间距比例1.0-4。己16-17煤层煤厚3.5m,为主采煤层。为降低己16-17煤层的瓦斯压力,实现安全高效生产,该矿以已15煤层为保护层,采用上保护层开采技术改变具有突出危险的煤层瓦斯赋存状态,降低被保护层的瓦斯压力。基于多孔介质流体流动理论,利用有限元数值模拟技术,模拟平顶山五矿超近上保护层的开挖过程,分析被保护煤层的瓦斯流动过程和煤层瓦斯压力的变化规律,论证保护层开采技术可以改变高突、高瓦斯煤层瓦斯赋存状态的可行性。     

松软煤层瓦斯钻孔失稳分析及动态密封技术

松软煤层钻孔在钻进及抽采瓦斯过程中,容易发生钻孔形变、缩径、坍塌甚至堵孔等工程问题,造成瓦斯钻孔成孔率低、密封性差、服务时间短及瓦斯抽采阻力大等抽采问题。针对上述技术难题,基于松软煤层的构造演化过程,分析了自重应力、构造应力、采动应力及瓦斯应力等因素对松软煤层瓦斯钻孔稳定性的影响,得出了松软煤层钻孔的多应力耦合作用失稳机制。同时,针对松软煤层瓦斯钻孔失稳规律,提出以护孔为基础,自适应动态密封为关键的"护-封"一体化松软煤层瓦斯钻孔密封技术。工程试验结果表明,该技术可使单孔瓦斯抽采体积分数增加至90%以上,单孔瓦斯体积分数提高2~3倍,且抽采浓度稳定。      

Spatial variation of selenium in Appalachian coal seams

Selenium (Se) is a trace element that can cause human physical deformations due to selenosis, and mutagenic changes on a range of sensitive macro-organisms. Previous studies indicated that Se enrichment is significantly greater in coal than in other rock units, suggesting a correlation between Se and coal bed proximity. Since coal extraction can cause a release of Se, some regulatory authorities have responded by requiring sampling of coal seams and adjacent rock for Se prior to issuing coal mining permits. This sampling is done under the assumption that Se in a small number of samples will be correlated to the Se concentrations throughout the strata they represent. For example, in one case a single continuous deep rock core was sampled for Se to estimate the concentrations of Se across a 2.52 km² proposed surface coal mine. This project examined the adequacy of such an approach using univariate statistics and variograms to determine the spatial variability and correlation of Se concentrations collected from six Appalachian coal seams. The results from all analyses showed no significant spatial correlation of Se within any coal seam examined. Given this lack of measured Se spatial correlation in Appalachian coal seams for scales as small as 0.10 km, it is unlikely that a Se spatial correlation exists in adjacent rock units at similar scales either, which is currently the assumption being made for sampling to minimize Se pollution from surface coal mining.     

穿层钻孔各煤层瓦斯抽采比例计算方法及应用

为了测定穿层钻孔多煤层瓦斯抽采各煤层瓦斯抽采比例及残余瓦斯含量,分别提出了相应的解决方法。计算穿层钻孔多煤层瓦斯抽采各煤层瓦斯抽采比例时,提出将煤层厚度、原始瓦斯含量、透气性系数的乘积作为瓦斯抽采相关量,将瓦斯抽采相关量归一化处理来计算,考虑了影响穿层钻孔瓦斯抽采的主要因素;预测穿层钻孔多煤层瓦斯抽采各煤层残余瓦斯含量时,利用原始瓦斯含量与吨煤瓦斯抽采量来计算,吨煤瓦斯抽采量与穿层钻孔瓦斯抽采总量、穿层钻孔在该煤层的瓦斯抽采比例及该煤层的质量有关。结果表明:提出的穿层钻孔多煤层瓦斯抽采各煤层瓦斯抽采比例计算方法,与贵州省青龙煤矿现场实测结果的最大相对误差仅为2.03%,能够满足工程实践的需要。      

贵州青龙煤矿碎软煤层区域瓦斯递进式抽采技术

针对碎软煤层瓦斯抽采钻孔存在轨迹不可控、成孔深度浅和瓦斯抽采效果差的问题,分析了现有瓦斯抽采钻孔回转钻进技术瓶颈,集成了基于长距离顺层钻进技术和双动力复合排渣技术的压风定向钻进技术,在此基础上提出了利用压风定向钻进技术,开展碎软煤层区域递进式瓦斯抽采技术。选取黔北煤田中部青龙煤矿21606运输巷道进行现场试验,在坚固性系数为0.37碎软煤层中,施工完成253个顺煤层压风定向钻孔,95%钻孔达到设计孔深,累计进尺超过3万m,单孔瓦斯抽采纯量是普通回转钻孔的10倍以上,单孔瓦斯抽采甲烷体积分数提高约50%以上。试验表明,采用压风定向钻进技术钻进碎软煤层钻孔轨迹可控,成孔率在95%以上,区域递进式瓦斯抽采技术具有无抽采盲区的显著优势,有效缓解了采掘接替紧张局面,提升了矿井瓦斯治理技术水平,为碎软煤层瓦斯治理提供了新的技术途径。      

软煤气动螺杆钻具定向钻进技术与装备

针对软煤钻进成孔深度浅、钻孔轨迹不可控、易出现瓦斯抽采盲区等问题，发明了气动螺杆钻具定向钻进技术，开发了由气动螺杆钻具、窄体定向钻机、随钻测量系统等组成的煤矿井下气动定向钻进技术装备。其中，气动定向钻进工艺和完孔技术，解决了松软煤层顺层定向钻孔长距离安全成孔和可靠护孔难题。在淮南某矿进行试验，试验钻孔30个，最大孔深300 m，平均见煤率92.9%，并全孔段安设筛管；钻孔抽采瓦斯纯量32万m3，试验区域煤巷平均掘进效率9.3 m/d，实现覆盖区域煤层安全高效回采。该技术的成功研发探索出软煤横穿工作面递进式瓦斯治理新模式。      

An integrated technology for gas control and green mining in deep mines based on ultra-thin seam mining

With the increasing demand for coal resources, coal mining has gradually entered into the deep strata of coal seams. Although the increase in mining depth improves energy security, it is associated with severe hazards, especially coal and gas outburst. Protective seam mining is an efficient method for gas control and has been widely used in major coal-producing countries. However, studies on deep ultra-thin protective seam (thickness 0.1–1 m, average thickness 0.5 m) mining and its related problems have been rarely reported. Focusing on the challenges resulting from deep mining (mining depth >1100 m) and the research gap, a coal and gas co-exploitation technique, which combines the gas control technology and green mining (including coal preparation and backfilling), has been proposed in this work. Significant benefits have been achieved in the twelfth coal mine of the Pingdingshan coalfield (study area) following the implementation of this technique. The application of the gas control technology markedly improved the gas drainage efficiency, promoted increased gas utilization, and reduced the greenhouse gas emission, providing notable economic and environmental benefits. In addition, implementation of green mining improved the coal quality, relieved the burden of the transport system, and, in particular, effectively prevented surface subsidence, thus protecting the ecological environment of the mining area, which offered significant economic, environmental, and social benefits. The practice in the twelfth coal mine could be used as a valuable example for coal mines with similar geological conditions.     

气动定向钻进技术在松软煤层条带瓦斯预抽中的应用

针对淮北矿区松软煤巷条带消突采用“底板巷—穿层钻孔”成本高且效率低现状,采用顺层气动定向钻进技术,按钻孔设计精准控制钻孔轨迹于预抽条带煤层中,通过钻孔抽采瓦斯实现煤巷条带消突。根据淮北矿区松软煤层特性,开展煤巷条带预抽瓦斯定向孔设计、气动定向钻进装备选型、软煤定向孔成孔与护孔工艺、抽采效果评价等研究。该技术成功应用于淮北某矿Ⅲ635工作面煤巷条带消突,试验7个孔深均大于300 m钻孔,且全程下筛管,创造两淮软煤矿区顺层钻孔372 m最深记录,成功保障煤巷掘进,减少底板巷和穿层钻孔,为软煤矿区煤巷条带瓦斯高效治理探索出新方法。      

Fracture Evolution and Accumulation and Dissipation Law of Energy During Ascending Mining

Ascending mining method is a widely used method in China for coal mine safety. To determine whether ascending mining method can eliminate or reduce the outburst risk or not in Xinzyao Mine, China, a numerical model was built by FLAC3D software to investigate the fracture evolution and accumulation and dissipation law of energy during the process of ascending mining. And a dual water blocking system was used to verify the fracture evolution obtained from the numerical model. The results show that FLAC3D model can predict the fracture evolution in overburden with a reasonable error. The height of water-conducting fractured zone of no. 14-3 coal seam is about 82.5 m, and it increases by 27 % after no. 12-2 coal seam is mined. The largest energy accumulated in no. 12-2 coal seam is about 32.5 kJ/m³ when mining it directly. The energy accumulated in no. 12-2 coal seam decreases by more than 40 % when ascending mining method is adopted. Ascending mining method can effectively eliminate the outburst risk of the upper coal seam. The research is helpful for the determination of ascending mining method and the further study of the prevention mechanism of rock burst.     

Design of gas drainage modes based on gas emission rate in a gob: a simulation study

In the process of working face advance in longwall coal mining, a great deal of gas relieved by the strata adjacent to the mining coal seam and the residual coal in gob migrates to gob. If the gas drainage method in gob is unreasonable, gas will accumulate in the upper corner and overrun in the return air flow. In the paper, a CFD (computational fluid mechanics) model of gob based on the actual geological conditions and gas drainage mode of 1262 working face of Dingji Coal Mine, China, was established. The gas drainage modes that should be taken to effectively control gas accumulation in the upper corner and gas overrun in the return air flow at different gas emission rates were discussed. The simulation results show that when the gas emission rate in the working face is lower than 20 m³/min, buried pipe drainage can effectively control gas accumulation in the upper corner and gas overrun in the return air flow. When gas emission rate there is between 20 and 30 m³/min, the two problems can be solved through cross-measure borehole drainage combined with buried pipe drainage. When gas emission rate there is higher than 40 m³/min, they can be effectively controlled through a three-dimensional drainage mode including buried pipes, cross-measure boreholes, and surface wells. Arranging surface wells within the fractured zone near the return airway can increase the gas drainage rate, and the gas concentration can reach over 85%; the gas concentrations of buried pipe drainage and cross-measure borehole drainage are 15~20% and 70~80%, respectively.     

贵州省煤层气(瓦斯)开发适用性技术分析

近年来在煤层气勘探开发实践中遇到诸多技术瓶颈,针对其中关键技术适用性开发问题,基于贵州地区煤储层呈薄煤层群赋存且构造复杂的地质背景,结合贵州地区煤层气成功开发、利用案例,提出了适用于贵州复杂地质条件下的煤层气开发及利用技术。贵州地区不同薄煤层群可根据实际间距情况采用光套管合层压裂、可捞式桥塞分段压裂等技术,煤层松软地区要加强防煤粉压裂技术及缝内转向技术的综合利用;松软低透煤层群应优选首采层,采动卸压后瓦斯抽采效果较好,同时加强定向长钻孔"以孔代巷"、松软煤层全程下套管、低透煤层CO₂相变致裂或水力割缝等技术的综合应用,实践证明可有效增强瓦斯抽采效果。      

急倾斜上保护层开采瓦斯越流固-气耦合模型及保护范围

开采保护层是防治煤与瓦斯突出最有效的措施之一,其关键是保护范围的合理确定。针对急倾斜多煤层上保护层开采有效保护范围的划定问题,基于煤层瓦斯越流理论,根据煤岩层变形与瓦斯渗流的固-气耦合作用,建立了瓦斯渗流场方程和煤岩体变形场方程,得到了急倾斜上保护层开采瓦斯越流固-气耦合数学模型。以南桐矿区某矿上保护层开采为实例,通过多物理场耦合系统,建立了该矿上保护层开采瓦斯越流几何模型并进行数值计算,获得了上保护层工作面开采后被保护层瓦斯压力的分布规律,确定了上保护层开采的卸压保护范围。数值计算与现场考察试验结果具有一致性,由此验证了数值计算的合理性。研究结果可以对现场保护范围的划定及卸压瓦斯抽放等提供理论指导,具有实际工程意义。