液氮溶浸煤致裂增透的实验研究

发布时间：2018-05-07 12:59

本文选题：液氮溶浸 + 裂隙扩展　；参考：《河北科技大学》2015年硕士论文

【摘要】：随着我国的经济持续快速发展,所需的各种能源也不断增加。所以加大非常规能源如:煤层气的开发及利用是非常必要的。但煤层气储层都是低孔低渗透,所以在开采时需要人工造缝或使用压裂技术来改造储层使其增大渗透性以便于开采。在国家自然科学基金项目(51574139,51274079)资助下,本文通过液氮溶浸不同饱水度煤样的实验,观察记录溶浸前后煤样的微观、表观裂隙变化率?,波速变化率?等指标,分析不同饱水度对于液氮低温冻却作用下对煤样致裂的影响。并对煤样进行二次冻融,再次比对煤样1次溶浸与2次溶浸后各项指标的变化。分析得出(1)在液氮溶浸后,原煤内原生裂隙扩展并有新生裂隙萌生。(2)煤样的含水率对液氮溶浸的效果有很大影响,饱和试样在溶浸前后的裂隙面积变化和波速变化比干燥和自然含水率两组煤样要明显。(3)煤样二次溶浸后比第一次溶浸的效果明显,有些煤样在进行二次溶浸后碎裂。这表明经反复冻融可以加剧煤样内部结构改变。运用断裂力学方法,分析液氮冻却下原生裂隙扩展,结果表明在液氮冷却作用下,煤裂隙中当应力强度因子与断裂韧度相等时,煤裂隙发生扩展。若应力强度因子达不到裂隙的断裂韧度,煤裂隙不扩展。应用FLAC软件构建模型,分析钻孔煤注入液氮后冻却储层的渗透率演化。模拟发现在煤层注入液氮后会在钻孔附近出现0.16米的拉伸破坏带。在拉伸破坏区域,裂纹萌生和扩展,煤元的渗透性显著增加。
[Abstract]:With the sustained and rapid development of China's economy, the amount of energy needed is increasing. Therefore, it is necessary to increase the development and utilization of unconventional energy such as CBM. But the coalbed methane reservoirs are all low porosity and low permeability, so artificial fracturing or fracturing technology is needed to improve the permeability of the reservoirs in order to facilitate exploitation. Supported by the project of National Natural Science Foundation of China 51574139 (51274079), this paper observed and recorded the microscopic, apparent fracture rate and wave velocity change rate of coal samples before and after leaching by liquid nitrogen leaching experiments with different saturated degree coal samples. The effects of different saturation degrees on the cracking of coal samples under the action of liquid nitrogen cryopreservation were analyzed. The coal samples were frozen and thawed again, and the changes of the indexes after 1 and 2 times leaching of coal samples were compared again. The results show that the water content of coal samples has a great influence on the effect of liquid nitrogen leaching after liquid nitrogen leaching, the primary cracks in the raw coal extend and the new fissures sprout. 2) the moisture content of the coal sample has a great influence on the effect of liquid nitrogen leaching. The change of fracture area and wave velocity of saturated samples before and after leaching is more obvious than that of two groups of coal samples: drying and natural moisture content.) the effect of secondary leaching of saturated samples is more obvious than that of the first. Some coal samples are cracked after secondary leaching. This indicates that repeated freezing and thawing can aggravate the internal structural changes of coal samples. By using the method of fracture mechanics, the primary crack propagation under liquid nitrogen freezing is analyzed. The results show that when the stress intensity factor and fracture toughness are equal to each other, the coal fissure expands under the action of liquid nitrogen cooling. If the stress intensity factor does not reach the fracture toughness of the fracture, the coal fracture does not extend. The permeability evolution of frozen reservoir after injection of liquid nitrogen from borehole coal was analyzed by using FLAC software. It is found that the tensile failure zone of 0.16 meters will appear near the borehole after injecting liquid nitrogen into the coal seam. In the tensile failure zone, the crack initiation and propagation increase the permeability of coal element significantly.
【学位授予单位】：河北科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TE37

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