幂律流体在不同接触率裂隙介质中的渗流规律

Analysis of seepage law of power-law fluid in fractured media with different contact rates

  • 摘要: 铀矿是国家重要的战略资源,而砂岩型铀矿赋存于煤层之间的铀矿含水层中,当进行煤铀协调开采时,在上下部煤层开采的应力扰动下,常发生砂岩原有裂隙的接触变化。考虑到铀矿地浸开采中必然受非牛顿流体溶液的影响,为探究接触扰动下砂岩裂隙的非牛顿流体渗流规律,依据巴西劈裂形成的真实砂岩表面,进行数字化重构。针对幂律流体在不同接触率裂隙模型中的流动进行数值模拟,探究了接触率与幂律流体特性在压力场、速度场的耦合效应,揭示了接触扰动下槽流、涡流的发展规律,提出针对不同幂律流体,相同流向横截面积的大小对截面压力、流速的变化趋势。结果表明:接触率的增大会增强流动的非线性。在接触区附近出现明显的压力分割线,更小的幂律指数与更大的入口速度表现为更强的压力阻隔效应。接触区之间的槽道为流体加速区域,小黏度流体对槽道的加速效果更加敏感,同时易在回流区产生涡流且涡流面积随着速度的增大而增大。裂隙的横截面积与裂隙的渗流速度呈相反的关系,而对于压力分布,压力与横截面积并非单调对应而是沿流向可能存在上升区域。压力曲线的变化和速度曲线的变化趋势相反,这种对应关系随着接触率的减小而增大,且压力曲线的变化稍滞后于速度曲线的变化。此外,不同幂律指数、入口速度的幂律流体在不同接触条件下的流动状态差异较为明显,证实幂律流体的流动对于接触面积、幂律指数以及入口流速具有一定的敏感性。

     

    Abstract: Uranium ore is a critical strategic resource for nations. Sandstone-type uranium deposits, hosted in aquifers between coal seams During coordinated coal-uranium mining, the original fractures in sandstone frequently experience contact alterations under stress disturbances induced by the extraction of upper and lower coal seams Considering that in-situ uranium mining is inevitably affected by non-Newtonian fluid solution, in order to explore the seepage law of non-Newtonian fluid in sandstone fractures under contact disturbance, digital reconstruction is carried out based on the real sandstone surface formed by the Brazilian split. Numerical simulation was carried out on the flow of power-law fluid in fracture models with different contact rates. The coupling effect of contact rate and power-law fluid characteristics in pressure field and velocity field was explored, and the development law of groove flow and eddy under contact disturbance was demonstrated. The variation trend of the same cross-sectional area of flow direction on the cross-sectional pressure and velocity. The results indicate that the nonlinearity of the flow is enhanced with the increase of the contact rate. There is an obvious pressure division near the contact zone, and a smaller power-law index and a larger inlet velocity show a stronger pressure barrier effect. The groove between the contact zone is the fluid acceleration zone, and the small viscosity fluid is more sensitive to the acceleration effect of the groove, and it is easy to generate eddy on the back flow area, and the eddy area increases with the increase of velocity. The cross-sectional area of the fracture is inversely related to the seepage velocity of the fracture, and for the pressure distribution, the pressure and cross-sectional area are not monotonic, but there may be a rising region along the flow direction. The change of pressure curve is opposite to that of velocity curve, and the corresponding relationship increases with the decrease of contact rate, and the change of pressure curve lags slightly behind that of velocity curve. In addition, power-law fluids with different power-law indexes and inlet velocity have obvious difference in flow state under different contact conditions, which proves that the flow of power-law fluid is sensitive to contact area, power-law index and inlet velocity.

     

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