不同煤级煤液相侵入效应低场核磁共振实验研究

我国煤层普遍具有低透气性、高瓦斯含量的特性,在低透气性煤层增透方面,煤层注水、水力压裂、水力割缝等水力化技术得到了广泛应用,并取得了良好的瓦斯治理效果。然而水作为外侵液进入煤体,堵塞了瓦斯流动通道,降低了瓦斯解吸量,产生了水锁效应。为分析水力化技术造成水锁效应的内在机理,利用压汞实验分析了煤样孔容分布规律,以及利用扫描电镜分析了原始、饱水、饱CMC溶液煤样的微观结构,基于低场核磁共振技术研究了煤样在饱水状态以及饱CMC溶液状态下的液相滞留效应,并根据曲线相似度法分析了孔径与束缚流体饱和度的相似度。研究结果表明:CMC溶液可以溶解煤中的矿物质增加煤孔隙裂隙以及降低水在煤体表面的表面张力,从而达到解除水锁效应的目的;随着煤变质程度的增大,T 2截止值在逐渐减小,T 2截止值的数值与煤样孔径大小呈负相关;煤样的束缚流体饱和度远大于自由流体饱和度,煤样在饱水状态下的束缚流体饱和度比饱CMC溶液状态下高;高变质程度的煤大孔孔容少、微孔孔容多,使得水在煤孔隙中的毛细管力大,最终造成高阶煤的水锁效应严重;大孔孔容是影响束缚流体饱和度的主控因素,微孔起到正向促进作用,得到束缚流体饱和度S与大孔孔容V A、微孔孔容V D的耦合关系式:S=94.86-1078.96 V A+261.24 V D。滞留在煤体内的束缚水阻塞了瓦斯流动通道,是造成水锁效应的根本原因,增加煤层的孔隙裂隙以及选用合适的表面活性是减缓煤层水锁效应的有效措施。

基于核磁共振测试的煤层水锁效应解除方法

为提高煤层瓦斯抽采效果,提出利用核磁共振(NMR)无损害测试方法,结合煤矿实际需求,从孔隙负压和表面活性剂两个方面对煤层水锁效应解除方法进行实验研究。结果表明:随孔隙负压的增加,核磁共振T2截止值可分为3个阶段:"稳定—降低—稳定"阶段。当煤层内的孔隙负压小于360.9 Pa时,煤层内的外来水会堵塞煤体孔隙,产生煤体水锁效应;当孔隙负压大于769.6 Pa时,能够消除水分对煤层孔隙的封堵,解除煤层水锁效应。在表面活性剂方面,阴离子和非离子表面活性剂溶液可以解除煤体中的水锁效应,有利于瓦斯抽采,且阴离子表面活性剂溶液解除水锁程度要大于非离子表面活性剂溶液;阳离子表面活性剂溶液会抑制煤层水锁效应的解除,阻止瓦斯在煤层中的运移,抑制瓦斯的抽采。

基于酸热耦合作用的煤体微观孔隙结构演化规律研究

为了揭示酸热耦合作用在提高煤层透气性的作用机理,结合低温氮吸附法和压汞法在不同孔径测试下的优势,以X射线衍射(XRD)物相分析为辅助手段,从细微观多角度分析煤体孔隙结构。研究结果表明:酸热耦合条件对煤体孔隙结构有显著影响,且呈现随温度增加先增强后减弱的趋势;在50℃条件下,5%HF+5%HCl混合酸液对孔隙的改造作用最为显著,具体在微小孔阶段(低温氮吸附法测得)孔体积提高了22.3%,比表面积提高了23.9%,平均孔径提高57.1%,在可见裂纹阶段(压汞法测得)孔体积提高了110.2%。

煤层新型润湿剂的实验合成及性能分析

为提高煤层润湿性,降低煤尘对井下作业的危害,以天池煤作为研究对象,选取了海藻酸钠和新型非离子表面活性剂KNOX-6201,KNOX-1335和阴离子表面活性剂KNOX-RF经过正交实验进行复配,研究不同表面活性剂复配形成润湿剂对煤尘润湿性的影响。通过对复配溶液的表面张力、与煤样形成的接触角以及煤样的水分复吸率,得出最佳复配方案及分析原因。结果表明,非离子表面活性剂复配润湿剂的润湿性低于非离子与阴离子表面活性剂复配之后的协同润湿作用。对于同一掺比的混合溶液,煤尘表面的接触角会随着海藻酸钠的掺量增加而逐渐减小。当加入0.5 g海藻酸钠、1 mL阴离子表面活性剂KNOX-6201,1 mL非离子表面活性剂KNOX-1335和1 mL非离子表面活性剂KNOX-RF复配溶液的表面张力为26.587 mN/m,最终接触角为0.76°,煤表面的亲水性更强。此时,水分复吸率最大为23.73%,溶液对煤的润湿性能更好。本工作对研制新型煤层润湿剂,进一步提高表面活性剂的润湿性,降低煤矿开采过程中的煤尘具有重要意义。

Variable frequency of pulse hydraulic fracturing for improving permeability in coal seam

Variable frequency,a new pattern of pulse hydraulic fracturing,is presented for improving permeability in coal seam.A variable frequency pulse hydraulic fracturing testing system was built,the mould with triaxial loading was developed.Based on the monitor methods of pressure sensor and acoustic emission,the trials of two patterns of pulse hydraulic fracturing of single frequency and variable frequency were carried out,and at last fracturing mechanism was analyzed.The results show that the effect of variable frequency on fracture extension is better than that of single frequency based on the analysis of macroscopic figures and AE.And the shortage of single frequency is somewhat remedied when the frequency is variable.Under variable frequency,the pressure process can be divided into three stages:low frequency band,pressure stability band and high frequency band,and rupture pressure of the sample is smaller than that of the condition of single frequency.Based on the Miner fatigue theory,the effect of different loading sequences on sample rupture is discussed and the results show that it is better to select the sequence of low frequency at first and then high frequency.Our achievements can give a basis for the improvement and optimization of the pulse hydraulic fracturing technology.

Relaxation study of cement based grouting material using nuclear magnetic resonance

Aiming at actual condition of poor effect of hole sealing for the reason of poor cement paste fluidity in the process of coal mine gas drainage,by adding a water reducing agent,cement paste for hole sealing was produced.The changes of initial distribution,weighted average values and total relaxation signal intensity of transverse relaxation time(T 2) of water in pure cement paste and water reducing agent added cement paste were studied with low field proton nuclear magnetic resonance(NMR).The results show that there are four peaks in T2 distribution curves of cement paste:the first peak is related to the bound water in flocculation,the second and the third peaks are related to the water in flocculation,water reducing agent makes it extending towards the long relaxation time,increasing its liquidity,and the fourth peak is related to the free water.By using weighted average values of T2 and total relaxation signal intensity,hydration process of cement pastes could be roughly divided into four stages:the initial period,reaction period,accelerated period and steady period.By analyzing the periods,it makes sure that the grouting process should be completed in the reaction period in the site,and the drainage process should be started in the steady period.The results have great guiding significance to the hole sealing and methane drainage.

Kinetic characteristics of coal gas desorption based on the pulsating injection

In order to understand the kinetic characteristics of coal gas desorption based on the pulsating injection(PI), the research experimentally studied the kinetic process of methane desorption in terms of the PI and hydrostatic injection(HI). The results show that the kinetic curves of methane desorption based on PI and HI are consistent with each other, and the diffusion model can best describe the characteristics of methane desorption. Initial velocity, diffusion capacity and ultimate desorption amount of methane desorption after PI are greater than those after HI, and the ultimate desorption amount increases by 16.7–39.7%.Methane decay rate over the time is less than that of the HI. The PI influences the diffusion model parameters, and it makes the mass transfer Biot number B0 idecrease and the mass transfer Fourier series F00 increase. As a result, PI makes the methane diffusion resistance in the coal smaller, methane diffusion rate greater, mass transfer velocity faster and the disturbance range of methane concentration wider than HI.Therefore, the effect of methane desorption based on PI is better than that of HI.

Microscopic properties and sealing performance of new gas drainage drilling sealing material

The geological condition of Chinese coal mines are complex and high gassy,which account for ffty percent to seventy percent.Because of the abundant pores and cracks around the drainage drilling hole,the gas concentration attenuates rapidly,and the effective gas drainage period is short.The traditional sealing materials of yellow mud and cement-sand grout will readily shrink after the drilling hole is sealed,the sealing length is short and the sealing quality is not satisfactory.Currently widely used polyurethane material will shrink when it comes into contact with water,and the price is also very high.In this study,taking cement as a base material,a novel composite sealing material mixed by expansion admixture,additive,and fbrin and coupling agent was developed and the sealing performance and expansion property of the material were also studied and analyzed.The FEI Quanta TM 250 environmental scanning electron microscope was used to investigate the microstructure of material.The results revealed that the new composite sealing material had a desirable expansion performance and a defnite fluidity convenient for grouting.The solidifed material,combining closely with the drilling wall,possessed an adequate strength and was not easy to shrink.Compared to the conventional polyurethane,the gas drainage concentration by drilling sealing exceeded 40 percent,and the sealing capacity improves5 times,the sealing effect increases signifcantly.

脉动水力压裂频率与流量对裂隙演化的作用

脉动水力压裂能够通过强化煤体的疲劳损伤破坏有效改善煤层渗透特性,脉动频率和流量是影响脉动水力压裂煤岩致裂效果的关键参量,但是针对脉动频率和流量对煤岩水力压裂裂隙演化的影响机制研究还不够充分.依托研制的可以持续产生一定频率脉动压力波的脉动水力压裂实验系统,开展了不同脉动频率和流量的脉动水力压裂物理相似实验,分析了静压压裂与脉动压裂压力曲线、声发射能量率、累积能量以及试件宏观破裂形态.结果表明:相同流量时,和静压压裂对比,脉动压裂在增压阶段和峰值阶段表现出不同的特征,其压力上升趋势呈"内凹"特征,后期增速高于前期,且疲劳作用时间长,破裂压力低,裂隙扩展形态复杂,随着脉动频率降低,这些特征更加明显;相同脉动频率时,流量越小,疲劳作用时间长,破裂压力低,裂隙越发育.在作用效果上,脉动频率和流量有一定的相似之处,脉动频率和流量越高,压裂效果越接近静压压裂,而在作用机理上,脉动频率改变了单位时间内的脉动波对试件的冲击次数,流量则是通过脉动波的幅值改变脉动压裂的疲劳效应.结合两个参量组合特点,提出了脉动频率与流量协同控制的脉动压裂工艺.

CO_(2)注入下煤层气产出及储层渗透率演化规律

为研究CO_(2)注入对煤层气(CBM)抽采及储层渗透率演变的影响,建立了考虑气体流动、竞争吸附、温度变化以及煤体变形的热-流-固耦合模型,通过对CBM和CO_(2)注入强化煤层气开采(CO_(2)-ECBM)过程的模拟,分析了煤层气产出及储层渗透率演变规律,提出了定量表征各参数影响程度的评价方法。结果表明CO_(2)注入3 600 d后煤层气累积产量(4.6×10^(4) m^(3))约为CBM抽采的5.75倍。CBM抽采过程中储层渗透率呈“降低-增加”趋势,其变化主要因CH解吸影响,相对影响系数约为0.57。其次因体积应变和孔隙压力影响,相对影响系数分别为0.2和0.23;CO_(2)-ECBM过程中储层渗透率呈“轻微增加-降低-显著增加-降低”趋势,其变化主要因CO_(2)吸附影响,相对影响系数为0.4,孔隙压力对渗透率的影响极小,其相对影响系数仅为0.02。

瓦斯抽采钻孔动态密封黏液型材料实验研究

为解决动态密封方法中现有黏液材料无法有效封堵煤岩漏气通道的问题,本文对钠基膨润土进行了改性研究。以钠基膨润土为基料,选取黏合剂羧甲基纤维素钠(CMC)、保水剂聚丙烯酰胺(PAM)和表面活性剂脂肪酸甲酯磺酸钠(MES)作为添加剂,研制出一种能与煤壁紧密结合的动态密封黏液型材料。通过单因素实验分别考察了表面活性剂掺量、保水剂掺量及水料比的变化对材料黏度及流动性的影响,掌握了各因变量随自变量的变化趋势。在此实验基础上,根据正交实验原理设计了三因素三水平17组配比实验,对17组实验所得黏液的黏度进行了统计,根据30 min内所得材料黏度值进行拟合与回归性分析,得到了拟合二次回归方程。其次,通过方差分析、等高线分析及响应曲面分析判断出各因素交互性对实验结果的显著性,分析表明3因素显著性排序为:保水剂>水料比>表面活性剂。最后,利用Design-Expert软件得出黏液材料的最佳配比为:表面活性剂4%,保水剂0.8%,水料比10∶1。为验证动态密封黏液型材料的高效性,选取漳村煤矿进行现场实验,并对30天内瓦斯抽采数据进行统计分析。实验表明:试验孔瓦斯抽采浓度比传统黏液材料封孔提高了24.57%,瓦斯抽采时间延长了1.5倍,瓦斯抽采流量得到显著提升,达到了煤矿瓦斯高效抽采的目的。