影响水平井注水泥顶替效率主要因素的数模分析研究

Analysis and Research on Numerical Simulation of the Main Factors Affecting Cementing Displacement Efficiency at Horizontal Wells

摘要:

水平井注水泥过程中，顶替效率的高低受多种因素的影响。其中，套管偏心度、冲洗液流变性能以及冲洗液与钻井液的密度差的影响较为突出。为了解水平井固井注水泥过程中各种影响因素的作用规律，借助流体力学软件Fluent，建立了偏心水平井三维模型，采用流体体积法（vof）进行了冲洗液顶替钻井液的数值模拟研究。模拟井筒直径为215.9 mm（81/2 in），模拟套管外径为177.8 mm（7 in），环空长度为300 m，冲洗液顶替速度为1 m/s，套管偏心度根据具体算例选取0、0.2、0.3、0.4。模拟结果表明：顶替效率随套管偏心度增加而降低，适当提高水泥浆流性指数，降低稠度系数有利于提高顶替界面的稳定，缩短界面长度，提高顶替效率。当冲洗液与钻井液之间形成正密度差关系时有利于顶替效率的提高。

关键词:水平井固井;顶替效率;fluent软件;偏心度;冲洗液流变性能;密度差

Abstract:

There are many factors which affect the displacement efficiency in the cementing process at horizontal wells. In these factors, the eccentricity of casing, rheological property of flushing fluid and density difference between flushing fluid and drilling fluid are prominent. In order to understand the influence of various factors on horizontal cementing, three-dimensional model of eccentric horizontal well was established by CFD software and numerical simulation study was made on drilling fluid being displaced by flushing fluid by means of VOF method. The inner and outer diameters of the simulated wellbore and casing are 177.8mm（7in）and 215.9mm（81/2in）respectively, the length of annulus is 300m, the displacement velocity is 1m/s and the casing eccentricity is selected 0，0.2，0.3 and 0.4 separately according to the specific example. The simulated results indicate that the eccentricity of casing at horizontal wells is unfavorable to cementing displacement efficiency, and increasing flow behavior index and decreasing consistency index are helpful for improving the stability of displacement interface, reducing its length and enhancing displacement efficiency as well. Meanwhile, when the positive density difference between flushing fluid and drilling fluid is formed, it is conducive to the improvement of displacement efficiency.

Key words:horizontal cementing; displacement efficiency; Fluent software; eccentricity; rheological property of flushing fluid; density difference