热力耦合作用下深部煤层渗流规律试验研究

On the deep coal seam seepage regularity of the thermo-mechanical coupled effect

为了进一步揭示深部煤岩渗透率的变化规律,进行了高有效应力和高温条件下煤体渗透规律测定试验。结果表明:随着有效应力的增大,煤层渗透率呈现递减趋势;温度升高,煤体出现膨胀现象,渗透率减小。初步提出了热力耦合作用下含瓦斯煤渗透率影响机理,即温度升高,煤固体骨架膨胀,试件内部孔隙裂隙体积减小,瓦斯渗流通道减小,渗透率减小;有效应力增大,煤体孔隙裂隙被压缩,导致渗透率逐渐减小。

To disclose the permeability of deep coal seam and modify the current three-axial permeameter by adding heating system, this paper intends to introduce our experimental results of various combinations among the axial compression, confining pressure, pore pressure and the temperature change. We have also measured the permeability change under the high effective stress and high temperature, and generalized the transportation regularity of CH4 under the thermo-mechanical coupling. And, then, based on the above research results, we have tentatively proposed the influenial mechanism of the permeability in the coal containing gas in the action of thermo-mechanical coupling via the formula calculation and theoretical analysis. That is to say, it can be concluded that the volumetric stress tends to change non-linearly with the permeability of the coal sample, whereas the permeability increases proportionally with the high pore pressure and the volumetric stress decreases with the permeability of the sample. Thus, the alternation of permeability is likely to be able to meet the exponental function. At the same time, the effective volumetric stress has a great effect on the permeability. With the increase of the effective stress, the internal fractures tend to get compressed so as to lead to the reduction of the permeability. Therefore, the relation between the effective volumetric stress and the permeability tends to be negatively exponential. On the other hand, if the temperature rises, the coal solid skeleton should expand, but the volume of pore and fracture in the specimen tends to decrease, and so does the gas seepage channel and the permeability. If the heating process goes on, it is likely to find the significant effect on the coal sample temperature stress. And, in turn, the thermal expansion of the coal sample may result in the closure of the crack effect of the coal, the reduction of the seepage channel, and the coal sharpening attenuation of the permeability. In such a case, if the temperature rises by over 55℃, the coal fracture tends to get closed and then stabilized, the permeability attenuation would likely to come to a stop. Based on the above mentioned studies over the high temperature changes that are likely going on in the process of deep coal seam under the coupled action of heat, we have worked out the changing regularity of the permeability of experimental research, which proves to be in conformity with the results of the experiment we have done. Therefore, the conclusion of this paper is expected to be able to provide an experimental basis for the deep coal seam gas migration rule influenced by thermo-mechanical coupling action, which can shed a light to the geological mechanism of the coal-gas exploitation and prevention of coal-gas outburst.