基于图像识别的裂隙煤层气非Darcy渗流模拟

Simulation of Non-Darcy Gas Flow in Image-Recognized Real Coal-Bed Fractures

煤层气在煤岩裂隙中流动时,由于其粘度系数较小,很容易产生非Darcy现象。因此,考虑煤层气的非Darcy渗流将会使得研究结果更加客观和准确,对煤层气开采具有实际意义。首先将实物裂隙高清拍照导入Matlab软件中进行图像二值化处理,再利用COMSOL软件对二值图像进行模型重构和数值模拟。模拟结果显示,煤层气渗流速度随着裂隙尺度的变化而不断改变,速度随时间不断增加,但区域渗流速度分布状态保持不变。与Darcy结果的对比分析可知,相同压力梯度下,考虑非Darcy因素的产气量要明显小于仅考虑Darcy因素的情况。同时,结果显示,在渗透率不同的煤裂隙中,煤层气的渗流速度不同。渗透率较大时,渗流速度相对较大,同样,渗透率较小时,渗透速度较小。

When coal-bed methane flows in coal fracture, it easily found out the non-Darcy phenomenon resulted from the relatively low viscosity coefficient of coal-bed methane. So, considering the non-Darcy seepage, the research result would be more objective and accuracy which has significant meaning in coal- bed methane exploitation. At first, the high qualified image of real fracture was introduced to Matlab soft- ware to be binary processed. Then, the binary image which has been processed in the first step was intro- duced to COMSOL software to reconstitute the fracture image so as to simulate the non-Darcy seepage of coal methane. The simulation result showed that the seepage velocity was changing with the scale of frac- ture and the seepage velocity kept on increasing. While, as time went on, the whole flowing state re- mained constant. At last, the result of seepage velocity profile of coal-bed methane in real fracture could be obtained at different time. Meanwhile, through analyzing the comparison between the non-Dacry seep- age velocity and Darcy seepage velocity, the conclusion was draw that coal-bed methane seepage in frac- ture was non-Darcy seepage and the production which took consideration of non-Darcy was less than that of Darcy seepage at the same pressure gradient. Meanwhile, the seepage velocity was changing with the different permeability of coal fractures. The velocity was relatively high in large permeability and low in small permeability.