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.     

Principle and engineering application of pressure relief gas drainage in low permeability outburst coal seam

With the increase in mining depth, the danger of coal and gas outbursts increases. In order to drain coal gas effectively and to eliminate the risk of coal and gas outbursts, we used a specific number of penetration boreholes for draining of pressure relief gas. Based on the principle of overlying strata movement, deformation and pressure relief, a good effect of gas drainage was obtained. The practice in the Panyi coal mine has shown that, after mining the Cllcoal seam as the protective layer, the relative expansion deformation value of the protected layer C13 reached 2.63%, The permeability coefficient increased 2880 times, the gas drainage rate of the C13 coal seam increased to more than 60%, the amount of gas was reduced from 13.0 to 5.2 m3/t and the gas pressure declined from 4.4 to 0.4 MPa, which caused the danger the outbursts in the coal seams to be eliminated. The result was that we achieved a safe and highly efficient mining operation of the C 13 coal seam.     

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.     

Test studies of gas flow in rock and coal surrounding a mined coal seam

An analysis of the variation rule of abutment pressure at the mining working face in a single coal seam and the mechanical behavior of surrounding rock during stoping is presented. Consideration of the elastic and plastic deformation zones that develop during the mining process allowed the determination of a relationship between horizontal stress and vertical stress. Based on this, a confined pressure unloading test was conducted by the use of the “gas-containing coal thermo-fluid-solid coupling 3-axis servo seepage” experimental apparatus. Thus, gas flow patterns in the elastic and plastic zones were derived from an experimental point of view. Darcy’s law and the Klinkenberg effect were used to derive a gas flow equation for the elastic and plastic stress fields. The study of gas flow phenomena at the working face during coal mining is of great importance for the study of gas migration and enrichment patterns.     

本煤层超前卸压瓦斯抽采的固-气耦合试验

对不同工作面推进速度条件下的超前支承压力演化规律及瓦斯抽采量的变化规律进行了对比分析,对不同轴压卸载起始点、不同围压卸载速度情况下的煤岩固-气耦合规律进行了试验研究.结果表明：轴压、围压同时卸载过程中,煤样经历了应变回弹、应变增加及应变软化3个阶段,轴压卸载起始点越小、围压卸载速度越慢,应变回弹过程越明显.反之,煤样越快进入应变增加和应变软化阶段.固定围压、加载轴压过程中,煤岩渗透率逐渐降低,瓦斯流量变小.轴压、围压同时卸载过程中,煤岩渗透率由缓慢增大到快速增大.当轴压、围压卸载到一定程度后,煤岩渗透率发生突跳.轴压卸载起始点越高、围压卸载速度越快,煤岩渗透率发生突跳时的轴压卸载量越小.     

巨厚火成岩对煤层瓦斯赋存及突出灾害的影响

通过采用火成岩取芯化验、煤样测试及现场观测等方法,分析了海孜煤矿10煤层覆岩中巨厚火成岩的力学性能,探讨了巨厚火成岩对远程10煤层瓦斯赋存与突出灾害的影响.结果表明:10煤层受巨厚火成岩的高温烘烤作用,煤体变质程度增高,煤层瓦斯吸附量增大,极限吸附量达到31.6753 m3/t;同时,巨厚火成岩均厚达120 m,单轴抗压强度平均为144.21 MPa,为矿井的主关键层,其阻碍了煤层瓦斯逸散,使煤层瓦斯含量高,且由于巨厚火成岩长期保持不断裂,导致10煤层工作面两端应力集中影响范围大大增加,达到100 m左右,更易具备煤与瓦斯突出的必要条件.     

Mechanism and control technology of strong ground pressure behaviour induced by high-position hard roofs in extra-thick coal seam miningOA

This work aimed at revealing the mechanism of strong ground pressure behaviour(SGPB) induced by high-position hard roof(HHR). Based on the supporting structures model of HHR, a modified voussoir beam mechanical model for HHR was established by considering the gangue support coefficient, through which the modified expressions of limit breaking span and breaking energy of HHR were deduced.Combined with the relationship between the dynamic-static loading stress of supporting body(hydraulic support ...     

“三软”煤层综放开采避开动压沿空留巷方法及应用

为实施"三软"煤层综放面沿空留巷,掌握留巷围岩结构和矿压变化规律,以新登煤矿31061综放面为研究对象,研究采空区侧向覆岩结构和应力分布,综放面后方沿空留巷变形和顶板压力分阶段变化规律,提出了避开动压沿空留巷方法,并在现场进行了工业试验。研究表明:(1)31061采空区侧向煤壁变形量大,应力降低区范围大,应力集中影响范围达到煤体内部30 m。(2)留巷矿压显现分为3个阶段。工作面后方30~40 m为巷道加速变形阶段,从工作面后方5 m留巷变形速度持续增加,但顶板压力升高较慢;工作面后方40~70 m为变形持续阶段,此阶段巷道变形速度保持稳定,顶板压力快速升高,临时支架产生变形破坏;工作面后方70 m以后为变形稳定阶段,此阶段变形速度明显降低,顶板压力趋于稳定。(3)避开动压沿空留巷方法是利用临时支护使留巷度过动压影响阶段,允许巷道有较大变形量,在工作面后方一定距离处对留巷进行扩修和加固。实践表明,该方法具有成本低、工艺简单、留巷后期稳定性好、留巷施工与采面生产互不干扰等优点,在条件适合的矿区值得推广。     

镶套轴承结构牙轮钻头的开发与应用

研制了一种新型的镶套轴承结构牙轮钻头,并进行了现场试验。试验结果表明,镶套结构的钻头轴承,承载能力有较大幅度提高,镶套轴承结构钻头能够适应高钻压钻井工艺的要求,具有良好的使用性能。     

异常高压低渗透砂岩储层应力敏感性定量模型——以东濮凹陷文13东沙三中油藏为例

为建立异常高压低渗透砂岩油藏储层应力敏感性定量模型,进行了模拟油藏条件的应力敏感性实验.实验采取改变围压(恒定孔隙流体压力)和改变孔隙流体压力(恒定围压)两种方式进行.研究结果表明:应力敏感性实验中改变围压与改变孔隙流体压力对有效应力的影响差异较大.改变围压比改变孔隙流体压力有效应力增加明显得多,改变围压的常规应力敏感性实验夸大了储层应力敏感性伤害程度.基于变孔隙流体压力应力敏感性实验,回归出各类储层的应力敏感性定量模型.其中,变孔隙压力液体应力敏感性模型与实际油田开发较为接近.异常高压低渗透砂岩油藏开发,油井见水后,采液指数、采油指数急剧下降;进入高含水开发阶段,采液指数回升,采油指数仍下降,此类油藏不适合采取提液手段稳定产量.