Safety analysis of stability of surface gas drainage boreholes above goaf areas

As longwall caving mining method prevails rapidly in China coal mines, amount of gas emission from longwall faces and goaf area increased significantly. Using traditional gas drainage methods, such as drilling upward holes to roof strata in tailgate or drilling inseam and cross-measure boreholes, could not meet methane drainage requirements in a gassy mine. The alternative is to drill boreholes from surface down to the Iongwall goaf area to drain the gas out. As soon as a coal seam is extracted out, the upper rock strata above the goaf start to collapse or become fractured depending upon the rock characteristics and the height above the coal seam. During overlying rock strata being fractured, boreholes in the area may be damaged due to ground movement after the passage of the Iongwall face. The sudden damage of a borehole may cause a Iongwall production halt or even a serious mine accident. A theoretical calculation of the stability of surface boreholes in mining affected area is introduced along with an example of determination of borehole and casing diameters is given for demonstration. By using this method for the drilling design, the damage of surface boreholes caused by excessive mining induced displacement can be effectively reduced if not totally avoided. Borehole and casing diameters as well as characteristics of filling materials can be determined using the proposed method by calculating the horizontal movement and vertical stain at different borehole depths.

Method for designing the optimal sealing depth in methane drainage boreholes to realize efficient drainage

The purpose of underground methane drainage technology is to prevent methane disasters and enable the efficient use of coal mine methane(CMM),and the sealing depth is a key factor that affects the performance of underground methane drainage.In this work,the layouts of in-seam and crossing boreholes are considered to analyze the stress distribution and failure characteristics of roadway surrounding rock through a numerical simulation and field stress investigation to determine a reasonable sealing depth.The results show that the depths of the plastic and elastic zones in two experimental coal mines are 16 and 20 m respectively.Borehole sealing minimizes the air leakage through the fractures around the roadway when the sealing material covers the failure and plastic zones,and the field test results for CMM drainage at different sealing depths indicate that the CMM drainage efficiency increases with increasing sealing depth but does not change once the sealing depth exceeds the plastic zone.Moreover,sealing in the high-permeability roadway surrounding rock does not have a strong influence on the borehole sealing performance.Considering these findings,a new CMM drainage system for key sealing in the low-permeability zone was developed that is effective for improving the CMM drainage efficiency and prolonging the high-concentration CMM drainage period.The proposed approach offers a valuable quantitative analysis method for selecting the optimum sealing parameters for underground methane drainage,thereby improving considerably the drainage and utilization rates of CMM.

Numerical simulation on the movement law of overlying strata in the stope with a fault and analysis of its influence on the ground gas drainage boreholes

In order to study the influence of a fault on the movement law of the overlying strata as well as its effect on the gas drainage boreholes, based on the practical situation of 1242（1） panel at Xieqiao Mine in Huainan, the Finite Element Method （FEM） model was built up, and the distribution of the stress field and the displacement field of the overlying strata in the stope with a fault were simulated by using the FEM software ANSYS. The results indicate that because of the existence of the fault, the horizontal displacement of overlying strata near the gas drainage borehole becomes larger than that in the stope without a fault, and the distribution of the stress field of the overlying strata changes greatly. When the working face is far away from the fault, the distribution of the stress field is approximately symmetrical. As the working face advances to the place 50 m away from the fault, the stress range at the right side goaf area is as twice as that at the left side. Here, the stress distribution area of goaf area and the fault plane run through, the fracture-connected-zone is formed. It can be presumed that the gas adsorbed in the coal and rock will flow into the fault zone along the fracture-connected-zone, which causes the quantity of gas drainage reduce remarkably.

Experimental and measured research on three-dimensional deformation law of gas drainage borehole in coal seam

Using self-researched gas drainage borehole stability dynamic monitoring device, three-dimensional deformation characteristics of borehole under steady vertical load were researched experimentally and systematically. This research indicated that under the action of steady loading, the mechanical deformation path of the simulated gas drainage borehole is gradually complicated, and the decay of the borehole circumferential strain is an important characterization of the prediction and early warning of borehole instability and collapse. The horizontal position of borehole occurs compressive strain, and the vertical of which occurs tensile strain under the action of vertical stress. At the initial stage of loading, the vertical strain is more sensitive than that in the horizontal direction. After a certain period of time, the horizontal strain is gradually higher than the vertical one, and the intersection of the borehole horizontal diameter and the hole wall is the stress concentration point. With the increase of the depth of hole, the strain shows a gradual decay trend as a whole, and the vertical strain decays more observably, but there is no absolute position correlation between the amount of strain decay and the increase in borehole depth,and the area within 1.5 times the orifice size is the borehole stress concentration zone.

Dynamic leakage mechanism of gas drainage borehole and engineering application

Borehole leakage not only affects the gas drainage effect but also presents considerable risk to human security. For the research on the leakage mechanism of gas drainage borehole, the rheological and visco-elastic-plastic characteristics were considered to establish the mechanical model of coal mass around borehole, which is used to analyze the leakage mechanism and deduce the dynamic leakage model. On the basis of the real coal seam conditions, the variation rules of the stress, leakage ring, and air leakage amount were analyzed through numerical simulation, and the influence factors of air leakage amount were also investigated to provide the theoretical basis for the sealing technology. Results show that the air leakage amount of borehole is inversely proportional to the increase in supporting stress and sealing length, and directly correlated with the increase in borehole radius and softening modulus. Using theoretical analysis, we design a novel active supporting sealing technology that can use grouting material to seal the fractures to reduce the leakage channels and also provide supporting stress to prevent borehole deformation. The engineering test results indicate that the average gas concentration with the novel active supporting sealing technology is increased by 162.12% than that of traditional polyurethane sealing method. Therefore, this technology not only effectively resolves borehole leakage but also significantly improves the gas drainage effect.

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.

An improved siphon drainage method for slope stabilization

The siphon drainage is an effective measure for the slope groundwater control. However,for the traditional siphon drainage, limitations such as siphon lift restriction and poor reliability in longterm service prevent it from being widely used. In this study, an improved siphon drainage method with inclined borehole penetrating the deep part of the slope is proposed to overcome the limitations suffered by the traditional method. Through experimental research, theoretical analysis and engineering practice,the reliability and capability of the proposed method are investigated. The results demonstrate that with the inclined pipe the height difference between the control point of the groundwater level and the orifice can be controlled to be less than the height of the water column corresponding to the local atmospheric pressure. As a result, deep drainage can be achieved.In addition, by controlling the diameter of siphon drainage pipe not larger than 4 mm, a plug flow can be formed in the siphon pipe, which can prevent air accumulation in the siphon process and a continuous and effective siphon drainage is achieved. Through a practical project running smoothly since September 2013, it is found that the proposed method can effectively drain the groundwater deep in the slope and the maximum drawdown of groundwater level in boreholes can reach 8.5 m with an average drainage flow of 5.5 m3/d. The practical results also illustrate that 4 mm siphon pipe can be used to realize deep slope drainage and restart siphon automatically.

Fracture evolution and pressure relief gas drainage from distant protected coal seams under an extremely thick key stratum

When an extremely thick rock bed exists above a protected coal seam in the bending zone given the condition of a mining protective seam, this extremely thick rock bed controls the movement of the entire overlying stratum. This extremely thick rock bed, called a ＂main key stratum＂, will not subside nor break for a long time, causing lower fractures and bed separations not to close and gas can migrate to the bed separation areas along the fractures. These bed separations become gas enrichment areas. By analyzing the rule of fracture evolution and gas migration under the main key stratum after the deep protective coal seam has been mined, we propose a new gas drainage method which uses bore holes, drilled through rock and coal seams at great depths for draining pressure relief gas. In this method, the bores are located at a high level suction roadway （we can also drill them in the drilling field located high in an air gateway）. Given the practice in the Haizi mine, the gas drainage rate can reach 73% in the middie coal group, with a gas drainage radius over 100 m.

Gas emission quantity prediction and drainage technology of steeply inclined and extremely thick coal seams

Gas emissions of workfaces in steeply inclined and extremely thick coal seams differ from those under normal geological conditions, which usually feature a high gas concentration and a large emission quantity. This study took the Wudong coal mine in Xinjiang province of China as a typical case. The gas occurrence of the coal seam and the pressure-relief range of the surrounding rock(coal) were studied by experiments and numerical simulations. Then, a new method to calculate the gas emission quantity for this special geological condition was provided. Based on the calculated quantity, a further gas drainage plan, as well as the evaluation of it with field drainage data, was finally given. The results are important for engineers to reasonably plan the gas drainage boreholes of steeply inclined and extremely thick coal seams.

Spontaneous combustion influenced by surface methane drainage and its prediction by rescaled range analysis

This study established numerical modeling using COMSOLTMto examine the influence of horizontal location and drainage ability of surface borehole on spontaneous combustion in longwall working face gob. Rescaled Range Analysis(R/S analysis) was employed to investigate the chaos characteristic of N_2/O_2 ratio from a surface borehole in 10416 working face gob, Yangliu Colliery, China. The simulation results show that there is always a circular ‘‘dissipation zone" around the drainage borehole and an elliptic ‘‘spontaneous combustion zone" in deep gob. Little influence was found on spontaneous combustion zone on the intake side of the gob but the width of spontaneous combustion zone in middle gob is enlarged, while the depth of spontaneous combustion zone near the return side is reduced. The R/S analysis indicates that the influence of surface borehole on spontaneous combustion can be divided into two stages by the chaos feature of N_2/O_2: safety drainage stage and spontaneous combustion initiating stage. It can be concluded that the methane drainage from gob through surface borehole can intervene in the distribution of spontaneous combustion zone in gob and the chaos feature of N_2/O_2 from surface borehole can effectively reflect coal spontaneous combustion condition in gob.

CFD simulations for longwall gas drainage design optimisation

Computational fluid dynamics(CFD) simulation is an effective approach to develop and optimise gas drainage design for underground longwall coal mining. As part of the project supported by the Australian Government Coal Mining Abatement Technology Support Package(CMATSP), threedimensional CFD simulations were conducted to test and optimise a conceptual design which proposes using horizontal boreholes to replace vertical boreholes at an underground coal mine in Australia.Drainage performance between a vertical borehole and a horizontal borehole was first carried out to compare their capacity and effectiveness. Then a series of cases with different horizontal borehole designs were simulated to optimise borehole configuration parameters such as location, diameter, and number of boreholes. The study shows that the horizontal borehole is able to create low pressure sinks that protect the workings from goaf gas ingresses by changing goaf gas flow directions, and that it has the advantage to continuously maintain such low pressure sinks near the tailgate as the longwall advances. An example of optimising horizontal borehole locations in the longwall lateral direction is also given in this paper.

自驱修孔钻头动力参数及钻齿结构研究

自驱修孔钻头是修复失效长钻孔的有效技术手段,为进一步提高修孔速度和瓦斯抽采效果,本文基于射流反冲理论,分析了射流反冲力与喷嘴参数的关系,构建了自驱修孔钻头旋转力学理论模型。采用LS-DYNA开展不同结构钻齿破煤过程,分析了不同钻进压力和扭矩作用下钻齿对煤体破坏形式和钻齿破煤体积变化规律,并开展了破煤实验验证数值模拟结果。形成了自驱修孔钻头参数确定方法,设计了自驱修孔钻头,并在郑煤集团超化煤矿22煤柱面底抽巷进行了工程实验。研究结果表明:(1)喷嘴张角α和偏心角β是决定钻进压力和扭矩分配的关键参数,通过调控张角和偏心角可实现钻进压力和扭矩的最优匹配。(2)相同钻进参数条件下,钻齿结构对破煤体积影响较大,阶梯钻齿破煤效果最优。在钻进压力为120N、扭矩0.6N·m时,阶梯型钻齿结构的修孔钻头能够实现钻进压力和扭矩最优匹配。(3)确定了最优修孔钻头结构参数为:钻头外径28 mm;后置喷嘴张角20°,偏心角90°;前置喷嘴张角90°,偏心角0°。(4)工程应用结果表明:瓦斯抽采纯量提高了1.96倍,瓦斯抽采体积分数提高了3.98倍,修孔速度提高了1.2倍。通过改进钻头动力参数及优化钻齿结构,设计的自驱修孔钻头在工程实践中达到了提高修孔速度和瓦斯抽采效果的目的。

四翼内凹刻槽钻杆高效排渣钻进技术研究

为解决松软煤层钻进钻孔排渣通道堵塞这一制约钻孔施工效果的关键难题,基于优化钻杆截面形状以增大排渣空间、预防钻孔堵塞这一理念,提出四翼内凹刻槽钻杆几何设计构想,通过孔内排渣阻力力学方程计算验证、钻杆排渣效果数值模拟,分析钻杆结构参数对排渣性能的影响,研制四翼内凹刻槽钻杆并在某矿进行工业性试验。研究结果表明:相较于传统圆状刻槽钻杆,四翼内凹刻槽钻杆在施工过程中具有更大的排渣空间,通过孔内沿程阻力计算对比,四翼内凹刻槽钻杆孔内沿程阻力较圆状刻槽钻杆低13%;数值模拟计算结果表明,当弧形内凹切槽对钻杆的圆心角α=35°、切入深度|EF|=4 mm时,渣体运移距离最大,平均运移速度最大,排渣性能最优;工业性试验表明,使用四翼内凹刻槽钻杆施工钻孔,班进尺长度和终孔深度得到显著提升。研究结果可为煤矿瓦斯抽采钻孔钻具设计提供参考。

高流态封孔注浆材料力学性能及水化机制

为提高深部矿井煤层气抽采效率,针对目前常见的封孔注浆材料存在的高分子封孔材料价格昂贵易燃、普通水泥材料渗透性差、粉煤灰等膏体材料强度不足等问题,采用超细水泥为基料研发一种高流态封孔注浆材料。通过对高流态封孔注浆材料开展力学性能试验研究、结合扫描电镜(SEM)、X射线衍射(XRD)等一系列试验的结果,揭示新型高流态封孔注浆材料水化机制。结果表明:高流态封孔注浆材料在水化初期就生成大量的水化硅酸钙(C-S-H)凝胶和钙矾石(AFt)晶体;随着水化反应的持续,水化产物的凝胶粒子充填材料中的孔隙。与普通水泥封孔注浆材料相比,材料的水化反应更迅速、更充分、整体结构致密,比普通水泥封孔注浆材料抗压强度提高3.68%,更有利于保持瓦斯抽采钻孔的稳定性,提高瓦斯抽采效率。

大直径高位定向孔一次钻扩技术及瓦斯抽采效果分析

针对“U”型通风回采工作面采动卸压瓦斯常规治理方式存在的综合效率低、治理成本高等问题,以山西晋城矿区某煤矿生产工作面为研究对象,提出采用φ200 mm大直径高位定向钻孔进行采动卸压瓦斯治理;基于该煤矿顶板大直径高位定向钻孔成孔技术难点分析,选型了关键钻进装备,包括ZDY20000LD型定向钻机、BLY460型泥浆泵车和多动力扩孔钻具;开发了复合强排渣定向钻进技术与多动力一次扩孔技术,实现了复杂地层条件下φ120 mm高位孔定向钻进与φ200 mm一次钻扩成孔,综合成孔效率较常规多次分级扩孔方式提高50%以上。瓦斯抽采效果表明:距煤层顶板30~40 m、距回风巷道40 m区域范围是采动裂隙密集发育区,钻孔平均瓦斯抽采体积分数保持在40%以上、最大瓦斯抽采纯量10.94 m^(3)/min,效果显著。

瓦斯抽采钻孔变形塌孔规律及精准监测技术研究

为推进瓦斯抽采钻孔精准智能化发展水平,基于分布式光纤监测和布里渊光学时域分析技术(BOTDA),以山西某矿为工程背景,开展了不同粒径配比下的钻孔堵孔模拟实验;构建了试验矿井堵孔率计算数学模型,揭示了钻孔变形塌孔发育规律,提出了适用于试验矿井的瓦斯抽采钻孔精准监测现场实施技术工艺,并通过现场试验对技术工艺的可行性和准确性进行了验证。结果表明:(1)光纤耦合体应变、模拟煤样堆积质量与钻孔变形塌孔间具有线性关系,随质量增加应变变化趋势相近,呈“陡-缓-陡”三阶段变化。通过分段拟合构建了适用于试验矿井的钻孔堵孔率计算数学模型。(2)通过误差分析,发现随着应变增加最大绝对误差先变大后变小再变大,中期最大绝对误差为19.48%,后期完全堵孔状态下的质量极值越接近不同配比煤样的平均质量极值误差越小。(3)基于上述数学模型解算,揭示了模拟堵孔过程中煤块首先在钻孔底部呈“凸”状堆积,随后滑向两侧,最后又在顶部聚集的塌孔演化规律,以应变值0、45.95×10^(-6)、72.19×10^(-6)为临界值区分塌孔前、中、后期,构建了适用于试验矿井的瓦斯抽采钻孔精准监测技术。通过现场应变监测结果分析,发现在孔周应力、扰动等因素作用下,失稳孔段孔周裂隙更易发育,塌孔程度随时间加剧。结合钻孔沿程堵孔率计算结果,对钻孔沿程变形塌孔情况进行了判断,对比钻孔窥视图可得,该精准监测技术判断结果基本符合实际观测情况。提出的以分布式光纤耦合体和BOTDA技术为基础的钻孔精准监测技术工艺可行、可靠,可为推进瓦斯抽采钻孔精准智能化发展水平提供参考。

高位定向长钻孔水力输送对接筛管护孔技术研究

保障高位定向长钻孔在工作面回采过程中的稳定抽采是实现“以孔代巷”的前提,而采用筛管完孔是维持钻孔稳定的有效护孔措施。为了实现高位定向长钻孔全孔段筛管护孔的工程应用,开发了钻孔内水力输送分组筛管自主对接完孔工艺技术,配套研制了ø95 mm筛管悬挂装置、ø95 mm玻璃钢筛管、ø100 mm封堵短节、ø140 mm钻头通水堵头以及ø95 mm分组筛管对接装置,并在皖北矿区两个煤矿的不同工作面顶板高位钻孔进行了水力输送分组筛管完孔现场试验。试验结果表明:玻璃钢筛管质量轻推送阻力小,可在倾角17°~26°的钻孔内人工连接长100 mø95 mm玻璃钢分组筛管,分组筛管输送过程中水压为1.0~1.5 MPa,输送到位时水压降为0.5 MPa以下,在泵量200~390 L/min下,分组筛管水力平均输送速度可达150~260 m/min,试验期间分组筛管输送到位时泵压变化明显,前后两组筛管对接可靠,可有效实现到位报信,成功实现ø153 mm高位定向钻孔内ø95 mm筛管的全孔段护孔,2个钻孔的筛管水力输送试验深度分别达到501、522 m,工作面回采120 d累计抽采瓦斯纯量分别为139945、176139 m^(3)。钻孔内水力输送对接筛管护孔技术为高位定向长钻孔全孔段大直径筛管护孔提供了可实现的技术解决方案,有助于保障高位定向长钻孔的瓦斯抽采效果,为煤矿井下“以孔代巷”的瓦斯治理模式革新提供技术支撑。

经额入路神经内镜手术在慢性硬膜下血肿治疗中的应用

目的评价经额入路神经内镜手术治疗慢性硬膜下血肿(CSDH)的疗效。方法分析80例CSDH病例的临床资料,依据手术方式,分为传统顶结节钻孔外引流术组(钻孔引流组,n=40),以及经额入路神经内镜下小骨窗血肿清除术组(神经内镜组,n=40),比较两组患者治疗有效率、术后1个月血肿复发率、手术时间和术中出血量。结果神经内镜组治疗有效率为95.0%,明显高于钻孔引流组的75.0%,神经内镜组术后1个月血肿复发率为5.0%,明显低于钻孔引流组的25.0%,神经内镜组手术时间为(54.1±7.5)min,较钻孔引流组的(40.7±9.4)min长,差异均有统计学意义(P<0.05)。神经内镜组术中出血量为(30.1±4.5)mL,与钻孔引流组的(27.1±6.4)mL比较,差异无统计学意义(P>0.05)。结论采用经额入路神经内镜手术治疗CSDH,能明显提高手术疗效,且术后血肿复发率极低。值得应用于临床。

长钻孔抽采条件下顶板瓦斯运移规律及减涌机理研究

顶板长钻孔瓦斯抽采是实现“以抽代巷”,实现顶邻近层瓦斯抽采,减少开采空间瓦斯涌出量的重要手段。结合顶邻近层瓦斯抽采减少回风顺槽上隅角瓦斯浓度工程实践,研究抽采条件下顶板瓦斯运移规律及其对工作面、回风顺槽瓦斯浓度涌出量减少作用机理,发现采用斜向高位钻孔群抽采造成的瓦斯压力降低区相互搭接,在回风顺槽顶板上方及左右两侧迅速形成1个沿巷道分布的低瓦斯压力区,该区域有效阻隔顶板瓦斯向回风顺槽的涌出;靠近采空区侧的顶板斜长钻孔对采空区瓦斯流动也有影响,可有效降低上隅角顶板附近瓦斯压力,降低瓦斯涌出量;抽采稳定后,工作面中部偏轨道顺槽一侧,仍会保有较高瓦斯压力区域,在工作面回采过程中应予以关注。

高突矿井未开采保护层区域瓦斯治理研究

为解决高突矿井试验工作面未开采保护层区域瓦斯浓度超限难题,基于COMSOL数值模拟分析了抽采参数对煤层瓦斯预抽效果的影响规律,通过物理相似模拟明确了采动卸压瓦斯导流通道。结合工程实际采掘进度,划分“掘进期”和“回采期”,分别开展瓦斯防治工作,采用立体式瓦斯抽采技术开展“顺层+穿层”钻孔瓦斯抽采。分析了掘进期高负压顺层钻孔与穿层钻孔的预抽效果,对比回采期断层附近穿层钻孔瓦斯浓度,研究了瓦斯抽采效果与工作面推进距离的关系。研究结果表明:不同布孔条件下,钻孔外侧瓦斯有效抽采半径在5 m左右,钻孔间距设置为10 m较为合理。掘进期,通过底抽巷施工穿层钻孔抽采邻近层瓦斯,配合顺层钻孔抽采使煤层瓦斯含量由24.37 m^(3)/t降至6.76 m^(3)/t,煤层瓦斯压力由1.62 MPa降至0.47 MPa;回采期,进风巷施工低负压高抽钻孔抽采上层采空区瓦斯,最大瓦斯浓度仅为8.7%。未开采保护层区域瓦斯抽采结合卸压瓦斯抽采技术成功消除了M18煤层的煤与瓦斯突出危险性。