低渗透性煤层气解吸机理及增透效果试验研究

发布时间：2018-06-28 00:27

本文选题：解吸机理 + 裂隙　；参考：《内蒙古科技大学》2015年硕士论文

【摘要】：我国煤层普遍具有低渗透性的特点，不利于煤层气的开采。为了提高煤层的渗透性，一些新的增透措施正在被研究利用，比如气爆增透技术、超声激励煤层增透技术，其中包括高压电脉冲技术。该项技术起初是被应用于石油开采中，后被嫁接到煤层气开采中，作为一种新的煤层增透技术，尚处于研究起步阶段，因此存在许多问题尚需解决。本文综合利用力学理论知识、试验研究和有限元软件模拟，对该项技术在钻孔注水煤层中的增透效果进行分析研究，得出以下成果：（1）理论分析认为煤层中裂隙的密度、长度、宽度以及贯通程度越发育，煤层的渗透性就越高，就越易于煤层气的解吸。根据岩石力学相关理论，推导出在试验中，孔壁产生新裂隙的起裂压力应不低于5.5MPa，理论计算结果与试验结果相吻合。然后通过断裂力学，对静水压和脉冲压力作用下裂隙尖端应力强度因子的变化过程进行分析，了解了裂隙扩展的演化规律。（2）根据以上理论分析在实验室进行了钻孔注水高压电脉冲煤层增透试验，模拟3MPa静水压以及3MPa静水压条件下施加10kv高压电脉冲后对煤样的致裂效果。然后利用CT扫描仪对试验试件进行扫描分析。由扫描结果可知：原煤样致密、硬度高、无裂隙分布。3MPa静水压作用下，煤样孔壁以及周边没有裂隙产生，而在3MPa静水压中施放10kv高压电脉冲后，孔壁以及周边的裂隙数目明显增多，说明水中高压电脉冲技术对煤样能够起到理想的增透效果。（3）利用ABAQUS扩展有限元法，对钻孔注水高压电脉冲煤层增透试验进行模拟，分析不同的静水压以及不同脉冲压力作用下，煤样裂隙的扩展情况。模拟结果表明：当钻孔内静水压达到3MPa时，裂隙长度未发生变化，宽度有一定的变化。而当静水压达到7.541MPa时，裂隙开始延长。当在静水压中施加脉冲荷载后，裂隙的延伸长度相比静水压显著增加，并且延伸长度随着初始放电能量的增大而增大，说明高压电脉冲对煤样的致裂效果要优于静水压致裂效果，且初始放电能量越高致裂效果越好。伴随着静水压和脉冲压力的作用，在裂隙尖端产生一定的拉应力，且拉应力值随着孔内压力的增大而增大，，这是导致裂隙扩展延伸的主要原因。
[Abstract]:Coal seam in our country has the characteristic of low permeability, which is unfavorable to the exploitation of coalbed methane. In order to improve the permeability of coal seam, some new antireflection measures are being studied, such as gas explosion antireflection technology, ultrasonic stimulation coal seam antireflection technology, including high-voltage electric pulse technology. This technology was first applied in petroleum exploitation, then grafted into coalbed methane production. As a new coal seam antireflection technology, it is still in the initial stage of research, so there are many problems still to be solved. In this paper, the antireflection effect of this technique in borehole water injection coal seam is analyzed and studied by comprehensive use of mechanical theory knowledge, experimental research and finite element software simulation. The following results are obtained: (1) theoretical analysis shows that the more developed the density, length, width and penetration degree of fractures in coal seam, the higher the permeability of coal seam and the easier the desorption of coalbed methane. According to the relevant theory of rock mechanics, it is deduced that the initiation pressure of new cracks in the hole wall should not be less than 5.5 MPA in the experiment, and the theoretical calculation results are in agreement with the experimental results. Then through fracture mechanics, the variation process of stress intensity factor at crack tip under hydrostatic pressure and pulse pressure is analyzed. The evolution law of fracture propagation is understood. (2) according to the above theoretical analysis, the antipenetration test of high pressure electric pulse coal seam with borehole water injection has been carried out in the laboratory. The cracking effect of coal samples under 3MPa hydrostatic pressure and 3MPa hydrostatic pressure with 10kv high voltage electric pulse was simulated. Then the CT scanner is used to scan and analyze the test specimen. From the scanning results, it can be seen that under the condition of dense coal sample, high hardness and no fracture distribution under hydrostatic pressure of .3MPa, there is no fissure in the wall of coal sample and around it, but the 10kv high pressure electric pulse is applied in the hydrostatic pressure of 3MPa. The obvious increase in the number of holes in the wall and the surrounding cracks shows that the high voltage electric pulse technique in water can play an ideal antireflection effect on coal samples. (3) Abaqus extended finite element method is used. The antireflection test of high pressure electric pulse coal seam with borehole water injection was simulated, and the crack propagation of coal sample under different hydrostatic pressure and different pulse pressure was analyzed. The simulation results show that when the hydrostatic pressure of the borehole reaches 3 MPA, the crack length does not change and the width changes to a certain extent. When the hydrostatic pressure reaches 7.541 MPA, the fracture begins to extend. When the pulse load is applied to the hydrostatic pressure, the fracture extension length increases significantly compared with the hydrostatic pressure, and the extension length increases with the increase of the initial discharge energy. The results show that the cracking effect of high voltage electric pulse is better than that of hydrostatic pressure, and the higher the initial discharge energy is, the better the cracking effect is. Along with the action of hydrostatic pressure and pulse pressure, a certain tensile stress is produced at the crack tip, and the tensile stress value increases with the increase of the pressure in the hole, which is the main reason leading to the extension of the fracture.
【学位授予单位】：内蒙古科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TE37

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