薄及中厚软煤层水力压裂煤岩损伤机理及瓦斯运移规律

发布时间：2018-05-23 11:34

本文选题：薄及中厚软煤层 + 水力压裂　；参考：《重庆大学》2016年博士论文

【摘要】：西南地区是我国重要的产煤基地和能源供应基地,不仅煤炭资源丰富,资源总量达到3866亿吨;而且煤层气储量达到4.21亿m3,开发潜力大。但西南地区煤层地质条件复杂,主采煤层厚度大多在0.8m~3.5m,以薄及中厚煤层为主;煤质普遍较软,f值在0.2~1;煤层透气性极低,渗透率在10-4 mD~10-3mD。导致西南地区煤层气开发及瓦斯灾害防治困难,严重制约清洁能源高效开发及煤炭安全生产。因此,如何大幅度增加薄及中厚软煤层透气性成为有效解决西南地区煤层气开发效率低灾害防治困难的关键问题。近年来,重庆松藻矿区将水力压裂技术引用到煤矿井下增透抽采煤层气,初步应用结果表明:平均单孔抽采纯量提高了3~5倍。但薄及中厚软煤层水力压裂裂缝起裂扩展规律及其对顶板损伤破坏机理、压裂过程中瓦斯运移富集规律仍然不明确。本论文采用理论分析、数值模拟、实验室及现场实验的方法,研究了薄及中厚软煤层水力压裂裂缝起裂扩展、煤岩损伤变形及瓦斯运移机理。主要研究结论如下:(1)建立了煤层水力压裂起裂压力及起裂方向计算模型,并揭示了煤层产状、地应力对煤层起裂压力、起裂方向的影响规律。煤层产状是影响薄及中厚软煤层水力压裂钻孔布置方式的主要因素,通过分析煤层产状和地应力共同影响下钻孔应力状态,根据最大拉应力理论,建立了煤层水力压裂钻孔起裂压力及起裂方向计算模型,并采用相似模拟实验对计算模型进行了验证。结果表明:起裂压力随水平主应力差、煤层倾向与最大主应力方位的夹角增大而减小,随煤层倾角增大而增大;随着煤层倾角减小,裂缝起裂方向由沿着煤层走向起裂逐渐向走向与倾向之间逆时针偏转,且偏转速度逐渐加快;随着煤层倾向与最大主应力方位的夹角增大,裂缝起裂方向由沿着煤层倾向起裂逐渐向煤层走向逆时针偏转,且偏转速度逐渐减慢。(2)通过构建薄及中厚软煤层水力压裂区域煤层—顶板损伤力学模型,揭示了水力压裂区域顶板损伤变形机理。理论分析了水力压裂克服煤体黏弹塑性致使顶板产生变形破坏,导致煤体卸压增透的基本原理。并通过将煤层水力压裂影响区域顶板简化为弹性薄板,建立薄及中厚软煤层水力压裂区域煤层—顶板损伤力学模型。在此基础上,利用FLAC3D分析薄及中厚软煤层水力压裂过程中顶板应力状态,揭示了煤层厚度、地应力、水力压裂工艺参数对顶板损伤变形的影响规律。(3)建立了薄及中厚软煤层水力压裂瓦斯运移模型,揭示了水力压裂瓦斯运移富集规律。理论分析了薄及中厚软煤层水力压裂过程中高压水驱替瓦斯的基本原理,根据渗流力学理论分析含瓦斯煤体水气驱替动力学过程,并建立薄及中厚软煤层水力压裂水气驱替两相渗流模型,揭示了煤体孔隙度、渗透率、瓦斯压力及水力压裂工艺参数对薄及中厚软煤层水力压裂瓦斯运移的影响规律。(4)研发出薄及中厚软煤层水力压裂技术工艺及压裂效果评价方法。根据薄及中厚软煤层水力压裂增透原理及赋存特征,研发出适用于薄及中厚软煤层水力压裂增透技术工艺;提出了“一看、二探、三测”的薄及中厚软煤层水力压裂增透效果评价方法。并将该技术应用于同华煤矿3121掘进条带增透抽采煤层气,结果表明:水力压裂范围为50m~60m时,瓦斯富集区位于30m~50m;与相邻未压裂的2127掘进条带相比,平均单孔瓦斯抽采纯量由1.75m3/d增加至10.36m3/d,提高了4.9倍;巷道掘进效率提高90.7%,平均风排瓦斯量从1.53m3/min降到0.45m3/min,降低了70.8%。
[Abstract]:Southwest China is an important coal producing base and energy supply base, not only rich in coal resources, the total amount of resources reached 3866 million tons, and the coal bed gas reserves reached 421 million m3, and the development potential is large. But the coal seam geological conditions in the southwest area are complex, the thickness of the main coal seam is mostly in the 0.8m~ 3.5m, which is mainly thin and medium thick coal seam, and the coal quality is generally soft and F value. In 0.2~1, the permeability of coal seam is very low, the permeability in 10-4 mD~10-3mD. leads to the difficulty in the development of coal bed gas and the prevention of gas disaster in the southwest region, which seriously restricts the efficient development of clean energy and the safe production of coal. Therefore, how to increase the permeability of thin and medium thick soft coal seam to effectively solve the low disaster prevention of coal seam gas development efficiency in Southwest China In recent years, hydraulic fracturing technology was quoted by hydraulic fracturing technology in coal mine in Chongqing. The preliminary application results showed that the average single hole extraction purity increased by 3~5 times. But the fracture expansion law of hydraulic fracturing fracture in thin and medium thick soft coal seam and its damage mechanism to the roof, and gas in the process of fracturing The law of migration and enrichment is still not clear. In this paper, the theoretical analysis, numerical simulation, laboratory and field experiments have been used to study the crack initiation and expansion, the damage and deformation of the coal and rock and the mechanism of gas migration in thin and medium thick soft coal seam. The main conclusions are as follows: (1) the calculation of the fracturing pressure and the cracking direction of the hydraulic fracturing of the coal seam The coal seam production is the main factor affecting the layout of the hydraulic fracturing drilling holes in thin and medium thick soft coal seams. By analyzing the joint stress state of the coal seam and the ground stress, the coal seam hydraulic pressure is established according to the maximum tensile stress theory. The calculation model has been verified by the similar simulation experiment. The results show that the crack pressure decreases with the horizontal main stress, the coal seam tendency decreases with the angle of the maximum main stress orientation, and increases with the increase of the coal seam inclination, and along with the decrease of the coal seam dip angle, the direction of crack initiation is along the edge. As the coal seam strike cracking gradually converse clockwise between trend and tendency, and the deflection speed increases gradually, with the increase of the angle of coal seam tendency and the maximum principal stress orientation, the direction of crack initiation is gradually deflected from coal seam tendency to coal seam to reverse clockwise, and the partial speed degree gradually slows down. (2) through the construction of thin and medium thick soft coal seam. The mechanical model of coal seam roof damage in hydraulic fracturing area reveals the mechanism of roof damage and deformation in hydraulic fracturing area. The basic principle of hydraulic fracturing to overcome the deformation and damage of the roof caused by the viscoelastic plasticity of the coal body and the pressure relief of the coal body is analyzed theoretically. On the basis of FLAC3D analysis thin and the stress state of the roof in the hydraulic fracturing process of medium and thick soft coal seam, the influence law of the thickness of coal seam, ground stress and hydraulic fracturing parameters on the deformation of the roof is revealed on this basis. (3) a thin and medium thick soft coal seam has been established. The model of hydraulic fracturing gas migration reveals the law of gas migration and enrichment in hydraulic fracturing. The basic principle of high pressure water displacement in the process of hydraulic fracturing in thin and medium thick soft coal seam is theoretically analyzed. The hydrodynamics process of gas and gas displacement in coal bearing coal body is analyzed according to the theory of seepage mechanics, and water and gas displacement in thin and medium thick soft coal seam hydraulic fracturing is established. The two phase seepage model reveals the influence law of coal body porosity, permeability, gas pressure and hydraulic fracturing parameters on the hydraulic fracturing gas migration in thin and medium thick soft coal seam. (4) research and development of thin and medium thick soft coal seam hydraulic fracturing technology and evaluation method of fracturing effect. The technology of hydraulic fracturing technology for thin and medium thick soft coal seam is developed, and the evaluation method of "one look, two exploration, three measurements" and the evaluation method of hydraulic fracturing effect in medium thick soft coal seam is put forward. And the technology is applied to the 3121 tunneling strip of Tonghua coal mine to increase the permeability and extraction of coal bed gas. The result shows that the hydraulic fracturing range is 50m~60m, tile. The concentration area is located in 30m~50m. Compared with the 2127 adjacent non fractured strip, the average gas extraction purity of the single hole is increased from 1.75m3/d to 10.36m3/d, increased by 4.9 times, the driving efficiency of the tunnel is increased by 90.7%, the average gas discharge amount is reduced from 1.53m3/min to 0.45m3/min, and 70.8%. is reduced.
【学位授予单位】：重庆大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TD712

【参考文献】