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红外加热储层煤岩热损伤特征扫描电镜及增透试验研究

SEM and permeability enhancement experiment study on thermal damage characteristics of coal-rock under infrared radiation

  • 摘要: 中国煤层气资源丰富,为提高煤层气抽采效率,减少煤矿开采过程中的瓦斯突出等灾害事故,提出了一种煤层气增产新技术原理—红外加热抽采煤层气。利用自制的红外加热渗流实验仪,采用扫描电镜及Matlab图像后处理相结合的方法,研究了煤岩样品在不同红外温度作用前后的孔裂隙发育扩展规律及渗透率变化特征。结果表明:红外辐射作用能够使煤岩体发生损伤破坏,红外温度越高,热损伤越明显。煤样孔隙率随着红外温度升高而增大,原生微孔隙裂隙相互贯通,新生裂隙逐渐增多,试样表面附着矿物颗粒随之减少,孔隙结构由狭长转向椭圆,各区间孔隙等效直径均大幅提升,小孔隙到大裂隙同步扩容,红外加热150 ℃时8~15 μm孔隙过渡阶段的孔容变化波动最大,提升为原始状态的4.35倍,总孔容增大高达99.5%;随着红外温度的升高,煤体渗透率亦随之增大,低温阶段原始孔隙率低的试样渗透率增幅偏小,原始孔隙率高的试件渗透率最高可增大130%,高温阶段试样渗透率均大幅跃升,较低温阶段其渗透率可高出9倍以上,较原始状态其渗透率可达到30倍以上,建立红外作用前后煤岩试样孔隙结构变化与宏观渗透率增加之间的统计定量表征关系,提出红外作用煤岩孔隙结构响应系数;红外辐射温度升高,能够有效地促进煤岩试样孔隙的增加与裂隙扩展,进而引发渗透率的增大,提高煤层气抽采效率。

     

    Abstract: China is rich in coalbed methane resources. In order to improve the efficiency of CBM extraction and reduce disasters such as coal and gas outbursts in the process of mining, a new technology principle of CBM production enhancement- infrared heating extraction of CBM is proposed. Using a self-made infrared heating seepage tester, the method of combining scanning electron microscopy and Matlab image post-processing was used to study the development and expansion of pores and fissures and the change characteristics of permeability of coal samples before and after different infrared temperatures. The results show that the effect of infrared radiation can damage the coal and rock mass, and the higher the infrared temperature, the more obvious the thermal damage. With the increase of infrared temperature, the porosity of coal samples increases. The primary micro pores and cracks are interconnected, the new cracks gradually increase, and then the mineral particles attached to the surface of the sample decrease accordingly. The pore structure changes from narrow and long to elliptical, the equivalent diameter of pores in each interval is greatly increased, and the volume of small pores to large cracks expands synchronously. When infrared heating at 150 ℃, the change of pore volume in the transition stage of 8-15 μm fluctuates the most, which is 4.35 times that of the original state, and the total pore volume increases by up to 99.5%. With the increase of infrared temperature, the permeability of coal also increases. The permeability of the samples with low original porosity in the low temperature stage increases slightly, but the permeability of the samples with high original porosity can increase up to 130%. The permeability of the samples in the high temperature stage jumped significantly, it can reach more than 9 times compared with the lower temperature stage, and 30 times compared with the original state. The statistics between the change of pore structure of coal samples before and after infrared action and the increase of macroscopic permeability are established, and the response coefficient of pore structure of coal under infrared action is proposed. The increase of infrared radiation temperature can effectively promote the increase of coal and rock sample pores and the expansion of cracks, which in turn leads to the increase of permeability and the improvement of CBM extraction.

     

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