考虑壁面浸润性的光滑岩体微裂隙渗流特性数值模拟研究

NUMERICAL SIMULATION OF THE SEEPAGE PROPERTIES OF A SMOOTH ROCK MICRO-FRACTURE CONSIDERING WALL WETTABILITY

在工程岩体中存在大量的微裂隙,由于隙宽尺寸微小,其壁面浸润性显著影响着流体在裂隙内的运动特性。为此,基于Shan-Chen伪势模型的格子Boltzmann方法,建立了光滑岩体微裂隙渗流的数值模型,并结合蒸汽中的悬浮液滴和壁面接触角的模拟,证明了该模型的有效性。最后,考虑壁面浸润性、裂隙隙宽、压力梯度及流体黏滞性等因素的影响,研究了重力驱动下光滑岩体微裂隙的渗流特性。研究结果表明:疏水壁面对附近流体的排斥作用产生加速效果,而亲水性壁面则产生阻碍作用,从总体变化趋势看,疏水壁面对微裂隙渗流的影响比亲水壁面更加显著。随着微裂隙隙宽的减小,其壁面浸润性对渗流流速的影响逐渐增大,且壁面亲/疏水性越强,隙宽对其渗流特性的影响越突出。裂隙的平均渗流流速随压力梯度的增加而增大,两者呈线性关系,且壁面疏水能力越强,其直线斜率越大。此外,流体的运动黏度越大,其流动阻力也越大,从而导致微裂隙渗流的平均流速越小,且流体的运动黏度与平均渗流流速呈反比例关系。

A lot of micro-fractures exist in rock.The wall wettability has a significant impact on the fluid flow due to their small width.Based on the Shan-Chen pseudopotential model,the lattice Boltzmann method is applied to establish the numerical model for studying the seepage properties of a smooth rock micro-fracture.The validity of the proposed model is proved by the simulation of a suspended liquid droplet in vapor and the wall contact angles.The seepage properties of a rock micro-fracture is studied considering the effects of the wall wettability,fracture width,pressure gradient and fluid viscosity.The results show that the hydrophobic wall has an accelerating effect due to the repulsion on the nearby fluid,while the hydrophilic wall has an obstructive effect.In general,the influence of the hydrophobic wall on the micro-fracture seepage is more significant than that of the hydrophilic wall.The effect of wall wettability on the seepage velocity increases with the decrease of the microfracture width.The stronger the hydrophilicity/hydrophobicity of wall is,the more significant the influence of fracture width will be.The average seepage velocity increases linearly with the increase of pressure gradient.The stronger the wall hydrophobicity is,the greater the linear slope will be.In addition,the larger kinematic viscosity of fluid is,the greater the flow resistance will be,which results in the decrease of the average flow velocity.In addition,there is an inverse relationship between the average flow velocity and the kinematic viscosity.