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.     

Application of pressure relief and permeability increased by slotting a coal seam with a rotary type cutter working across rock layers

Pressure relief to increase permeability significantly improves gas extraction efficiency from coal seams. In this paper we report results from simulations using FLAC^3D code to analyze changes in coal displacement and stress after special drill slots were formed. We investigated the mechanism of pressure relief and permeability increase in a high-gas and low-permeability coal seam through the modeling of gas flow. This allows the development of the technology. Slotting across rock layers in the coal seam with a rotary type cutter was then applied in the field. The results show that pressure relief and permeability increases from slotting the coal seam can increase the transport and the fracture of the coal. This expands the range of pressure relief from the drilling and increases the exposed area of the seam. The total quantity of gas extracted from slotted bore holes was three times that seen with ordinary drilling. The concentration of gas extracted from the slotted drills was from two to three times that seen using ordinary drills. The gas flow was stable at 80%. Improved permeability and more efficient gas extraction are the result of the slotting. The roadway development rate is increased by 30–50% after gas drainage. This technology diminishes the lag between longwall production and roadway development and effectively prevents coal and gas outburst, which offers the prospect of broad application.     

深部煤层瓦斯赋存规律及钻孔抽采有效半径研究

实测了新庄孜矿深部低透气性煤层的瓦斯压力、煤层透气性系数、瓦斯含量、瓦斯涌出衰减系数和自然排放半径等基础参数;在此基础上,数值模拟计算了钻孔抽采瓦斯的有效半径。研究结果表明,煤层的透气性是决定钻孔有效排采半径的主导因素。为提高低透气性煤层抽采瓦斯钻孔预抽消突效果,应积极采取措施提高煤层透气性系数。     

Effects of coal damage on permeability and gas drainage performance

Coal permeability is a measure of the ability for fluids to flow through coal structures. It is one of the most important parameters affecting the gas drainage performance in underground coal mines. Despite the extensive research conducted on coal permeability, few studies have considered the effect of coal damage on permeability. This has resulted in unreliable permeability evaluation and prediction. The aim of this study is to investigate the effect of coal damage on permeability and gas drainage performance. The Cui-Bustin permeability model was improved by taking into account the impact of coal damage on permeability. The key damage coefficient of the improved permeability model is determined based on the published permeability data. A finite-element numerical simulation was then developed based on the improved permeability model to investigate the damage areas and the permeability distribution around roadway. Results showed that the tensile failure occurs mainly on the upper and lower sides of the roadway while the shear failure symmetrically occurs on the left and right sides. With the increase in the friction angle value, the damage area becomes small. A good agreement was obtained between the results of the improved permeability model(c = 3) and the published permeability data. This indicated a more accurate permeability prediction by the improved permeability model. It is expected that the findings of this study could provide guidance for in-seam gas drainage borehole design and sealing, in order to enhance the gas drainage performance and reduce gas emissions into underground roadways.     

Technology and application of pressure relief and permeability increase by jointly drilling and slotting coal

Difficulties with soft coal seams having a high gas content and high stress levels can be addressed by a technology of pressure relief and permeability increase. Slotting the seam by auxiliary drilling with a water jet that breaks the coal and slots the coal seam during the process of retreat drilling achieves pressure relief and permeability increase. Improved efficiency of gas extraction from a field test, high gas coal seam was observed. Investigating the theory of pressure relief and permeability increase required analyzing the characteristics of the double power slotting process and the effects of coal pressure relief and permeability increase. The influence of confining pressure on coal physical properties was examined by using FLAC3D software code to simulate changes of coal stress within the tool destruction area. The double power joint drilling method was modeled. Field experiments were performed and the effects are analyzed. This research shows that there is an “islanding effect” in front of the joint double power drill and slotting equipment. The failure strength of the coal seam is substantially reduced within the tool destruction area. Drilling depths are increased by 72% and the diameter of the borehole is increased by 30%. The amount of powdered coal extracted from the drill head increases by 17 times when using the new method. A 30 day total flow measurement from the double power drilled and slotted bores showed that gas extraction increased by 1.3 times compared to the standard drilled bores. Gas concentrations increased from 30% to 60% and were more stable so the overall extraction efficiency increased by a factor of two times.     

潘三矿立井揭煤瓦斯抽采模拟研究

瓦斯抽采对于立井揭突出煤层起到重要的作用,准确的确定钻孔瓦斯有效抽采半径和合理的在待抽煤层中布置抽采钻场对煤层消突具有关键性作用。基于多孔介质中流体流动达西定律理论,采用COMSOL Multiphysics软件对该煤层瓦斯抽采进行了模拟。模拟结果表明,此煤层的瓦斯有效抽采半径为3 m,随着抽采时间的增加,煤层瓦斯压力逐渐的降低,但降低的速率会逐渐的减小。瓦斯抽采30天后,其残余的瓦斯压力为0．18 MPa ,这与现场实测的最大残余瓦斯压力0．2 MPa相接近,这说明了模型的可信性,其模拟结果可为瓦斯抽采设计提供参考。     

基于卸压开采的下向穿层钻孔抽采瓦斯技术

为了实现下伏被保护层的卸压瓦斯抽采最大化,本文提出了保护层开采采用“Y”型通风沿空留巷技术,同时配合下向穿层钻孔的立体式抽采瓦斯技术,优化确定了下向钻孔的技术参数、施工时间、粉尘防治等工艺难题。工程实践表明,下向穿层钻孔单孔抽采瓦斯纯量可达0．2m^3/min,最大约0．45m^3/min,浓度高达60～90％,高效稳定时间约20～30d,可实现卸压瓦斯的抽采最大化。     

地面群孔瓦斯抽采技术应用研究

为保证新集一矿突出煤层13-1煤北中央采区的安全开采,先后开采131103、131105等11-2煤层工作面作为保护层。首先在上述两个工作面共布置了6个地面钻孔,建立了地面群孔瓦斯抽采系统,预抽采动区被保护层13-1煤瓦斯。接下来对地面钻孔抽采瓦斯参数进行了考察,主要包括基于示踪技术考察了131105工作面采动卸压地面钻孔走向及倾向瓦斯抽采半径,统计分析被保护层瓦斯抽采率,同时就地面群孔与井下底板巷穿层钻孔瓦斯抽采两种方法进行了抽采率、工程费用等方面的对比。研究结果表明：新集一矿的地层条件下地面钻孔抽采煤层卸压瓦斯沿煤层倾向和走向的抽采半径分别不小于160m和240m;采动区地面群孔瓦斯抽采率达35%以上;地面钻孔相对比井下底板巷,在抽采瓦斯方面具有技术上可靠、安全、经济等优点。     

Numerical simulation of influence of Langmuir adsorption constant on gas drainage radius of drilling in coal seam

To determine reasonable distance of gas pre-drainage drillings in coal seams, a solid–gas coupling model that takes gas adsorption effect into account was constructed. In view of different adsorption constants,the paper conducted the numerical simulation of pre-drainage gas in drillings along coal seam, studied the relationship of adsorption constants and permeability, gas pressure, and effective drainage radius of coal seams, and applied the approach to the layout of pre-drainage gas drillings in coal seams. The results show that the permeability of coal seams is on the gradual increase with time, which is divided into three sections according to the increase rate: the drainage time 0–30 d is the sharp increase section;30–220 d is the gradual increase section; and the time above 200 d is the stable section. The permeability of coal seams is in negative linear and positive exponent relation with volume adsorption constant VLand pressure adsorption constant PL, respectively. The effective drainage radius is in negative linear relation with VLand in positive exponent relation with PL. Compared with the former design scheme, the engineering quantity of drilling could be reduced by 25%.     

煤层注水促抽瓦斯及其影响因素的数值模拟

为有效预防煤矿瓦斯灾害,获取煤层注水促抽瓦斯的合理参数,以常村煤矿2103工作面为例,依据多相渗流理论,采用Fluent软件的VOF模型及多孔介质模型耦合求解,对煤层注水促抽瓦斯技术及其影响因素进行数值模拟,并将模拟结果应用于现场,对比分析数值模拟与现场实测数据,二者基本吻合.研究结果表明:煤层瓦斯含量以注水孔为中心径向逐步降低,以抽采孔为中心径向逐步升高;注水前抽采阶段,随着抽采时间的增加,抽采范围逐渐增大,抽采孔瓦斯流量先快速下降,后逐步缓慢降低;注水促抽阶段,随着注水时间的增加,注水范围逐渐增大,注水流量逐步降低,煤层瓦斯含量缓慢升高,抽采孔瓦斯流量逐渐增加;注水后抽采阶段,随着抽采时间的增加,压力水覆盖范围持续增大,煤层瓦斯含量逐渐降低,抽采孔瓦斯流量逐渐减小.注水时机、注水时间、注水压力、注水方式、布置方式及钻孔间距是影响煤层注水促抽瓦斯效果的6个主要因素.瓦斯正常抽采20 d后,按照一注一抽方式及5 m间距布置注抽钻孔,在8 MPa煤层注水压力下间歇注水10 d,煤层注水促抽瓦斯效果较好.     

Interlayer interference mechanism of multi-seam drainage in a CBM well:An example from Zhucang syncline

Based on the characteristics of the strong volatility of physical property in vertical direction, high gas content, high resource abundance and large exploitation potentiality of coal reservoir in Bide-Santang basin of Zhina coal field, we study the generation mechanism of interlayer interference, propagation rules of reservoir pressure drop and influencing factors of gas productivity in CBM multi-seam drainage in the paper. On the basis of the actual production data of X-2 well of Zhucang syncline in Bide-Santang basin,by simulating the gas production process of a CBM well under the condition of multiple seam with COMET3 numerical simulation software, we analyze the influencing factors of gas productivity during the process of multi-seam drainage, and illuminate the interlayer interference mechanism of multiseam drainage. The results show that permeability, reservoir pressure gradient, critical desorption pressure and fluid supply capacity of stratum have great influence on gas productivity of multi-seam drainage while coal thickness has little influence on it. Permeability, reservoir pressure gradient and fluid supply capacity of stratum affect the propagation velocity of reservoir pressure drop and thereby affect the final gas productivity. Moreover, the influence of critical desorption pressure on gas productivity of multiseam drainage is reflected in the gas breakthrough time and effective desorption area.     

海石湾矿风井井筒含油气岩层突出危险性预测

为了预防砂岩突出，通过实验室测定了油气岩石的力学性质、岩石成分、显微结构、油气含量及透气系数，现场测定了片状岩芯的比例、钻孔变形、油气压力、油气岩石排放半径以及钻孔内油气排放量等． 根据上述多方面的测定结果，综合判断岩石突出的危险程度，为预防岩层突出提供了参数．     

凝析油气体系流固耦合相平衡计算新方法

在分析了孔隙介质内表面吸附、毛细凝聚、毛细管压力等界面物理化学效应和应力变形对孔隙介质中流体相态影响的现象学特征和影响机制的基础上,通过在大尺度空间常规流体相平衡热力学模型中引入界面物理化学效应的影响,同时通过高才尼-卡尔曼方程将毛细管半径与孔隙介质储渗特性的应力敏感性研究成果相关联,建立了同时考虑储层应力变形和界面物理化学效应影响的微孔隙尺度条件下的低渗特低渗凝析气藏多相流体流固耦合露点压力、p-T相图及定容衰竭相平衡热力学计算模型.该模型的初步应用表明,其相态模拟计算结果能更为合理地解释孔隙介质环境中的凝析油气体系相态特征实验研究结果.     

超低渗储层基质块弹性采出程度影响因素分析

随着近年来我国超低渗油气资源的快速开发,其弹性开采阶段的主控因素已引起广泛关注。为研究超低渗储层弹性开采阶段影响采收率的因素,将渗透率、黏度、衰竭压差及衰竭半径组合为4因素3水平正交实验,通过室内实验得出影响采出程度的排序为：衰竭压差>渗透率>衰竭半径>黏度。结合扫描电镜图像,分析采出程度除了与自身的初始弹性能有关外,还与应力敏感性及启动压力梯度有关。此外,对比分析渗透率、流度、流度 压差3种模式的启动压力梯度模型,通过数值模拟与实验数据的误差分析,优选出更趋近真实情况的模型为流度-压差模型     

超高压水力割缝强化抽采瓦斯技术研究

水力割缝是一种重要的强化瓦斯抽采增透技术,现已开始在低透气性突出煤层应用。为了进一步考察其实际效果,选取新集二矿1煤组220112工作面底抽巷实施了100 MPa超高压水力割缝试验。试验结果表明:割缝后,瓦斯抽采纯量平均0.77 m3/min,是未割缝钻孔的瓦斯抽采纯量(0.34 m~3/min)的2.26倍;1煤层组瓦斯抽采钻孔抽采30、60天的抽采有效半径为5 m、7.5 m,极限抽采半径为8 m,相比水力冲孔、未割缝钻孔抽采有效半径显著增加,超高压水力割缝强化抽采瓦斯技术具有广泛的应用前景。     

Numerical and experimental evaluation on methods for parameter identification of thermal response tests

Several parameter identification methods of thermal response test were evaluated through numerical and experimental study. A three-dimensional finite-volume numerical model was established under the assumption that the soil thermal conductivity had been known in the simulation of thermal response test. The thermal response curve was firstly obtained through numerical calculation. Then, the accuracy of the numerical model was verified with measured data obtained through a thermal response test. Based on the numerical and experimental thermal response curves, the thermal conductivity of the soil was calculated by different parameter identification methods. The calculated results were compared with the assumed value and then the accuracy of these methods was evaluated. Furthermore, the effects of test time, variable data quality, borehole radius, initial ground temperature, and heat injection rate were analyzed. The results show that the method based on cylinder-source model has a low precision and the identified thermal conductivity decreases with an increase in borehole radius. For parameter estimation, the measuring accuracy of the initial temperature of the deep ground soil has greater effect on identified thermal conductivity.     

单井注气吞吐过程中油气饱和度分布研究

建立了相对渗透率和毛管压滞后模型,对已有的黑油模型进行了改进,使得相渗和毛管压力在实际的油藏模拟中更加精确地体现出来,并使改进后的模型能有效地反映注气吞吐过程的真实动态。基于改进的黑油模型,对单井注气吞吐全过程的三个阶段：注气阶段、关井平衡阶段、开井采油阶段,油气的饱和度分布规律进行了模拟计算和结果分析,研究结果对实际的水平地层单井吞吐均具有一定的指导意义和作用。     

城市生活垃圾填埋场气压分布一维稳态分析模型

掌握填埋场气压分布是填埋气灾害控制和资源化利用的基础。提出了分层垃圾填埋体气压分布一维稳态分析模型及求解方法。该模型可分析含有给定抽气压力或给定抽气流量水平导气层的填埋体气压分布。采用该模型探讨了垃圾分层特征、封顶覆盖层下和填埋体内的高渗透性水平导气层、填埋体底部渗沥液导排系统兼作填埋气导排通道对填埋体气压分布的影响规律。通过参数分析得到以下结论：填埋体垃圾不考虑产气速率和固有渗透系数随垃圾埋深增加而减小（产气速率和固有渗透系数按埋深平均）会高估填埋体内气压;封顶覆盖层下和填埋体内设置水平导气层可有效降低填埋体内气压;填埋体底部填埋气导排通道对填埋气气压较大的深部垃圾降压效果较明显。分析结果表明,该模型可指导填埋气收集系统设计,如水平导气层位置和间距布置及抽气功率选择等。     

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.     

Induced drill-spray during hydraulic slotting of a coal seam and its influence on gas extraction

Hydraulic slotting can induce drill spray in a gassy, low permeability coal seam. This then influences subsequent gas extraction. This paper describes the drill spray phenomenon from a mechanical perspective and analyzes the effects of water jet damage during slotting. A simulation of the stresses around the drill hole and slot was prepared using FLAC-3D code. It helps explain the induction of drill spray during hydraulic slotting. The stress concentration around the bore increases as the diameter of the hole increases. As the hole enlarges the variation in stress also increases, which introduces an instability into the coal. This allows easy breaking and removal of the coal. Destruction of the coal structure by the water jet is the major factor causing drill spray. Energy stored as either strain or gas pressure is released by the water jet and this causes the coal to fracture and be expelled from the hole. Field tests showed the effect on gas extraction after slotting with drill spray. The concentration of gas increases after drilling. Compared to conventional techniques, the hydraulic slotted bore gives a gas concentration three times higher and has an effective range twice as far. This makes the gas extraction process more efficient and allows reduced construction effort.