偏心度和密度差耦合条件下水平井顶替界面特征研究

为了解水平井水平段偏心环空固井时的顶替界面特征，提高水平井水平段偏心环空固井的顶替效率，建立了考虑流态耦合与质量扩散的水平井水平段三维动态顶替数学模型，对水泥浆顶替隔离液过程中，偏心度和密度差耦合条件下的顶替界面形态进行了数值模拟。数值模拟结果表明:偏心度增大，偏心效应增强，顶替界面高边指进趋势增强；正密度差增大，浮力效应增强，顶替界面低边指进趋势增强；偏心度和密度差合适的耦合可使偏心效应和浮力效应达到临界平衡状态，此时顶替界面形态相对稳定且界面长度无明显增长，顶替效率最高。模拟结果为水平井水平段偏心环空固井提高顶替效率提供了理论依据。 

Horizontal Well Cement Displacement Interface Features under the Coupling of Eccentricity and Density Difference

To understand the features of the cement displacement interface in the horizontal section of the eccentric annulus and to improve horizontal section eccentric annulus cement displacement efficiency, a three-dimensional dynamic displacement mathematical model in horizontal section was established considering flow regime coupling and mass diffusion. The cement displacement interface morphology during cement displacement of the spacers was numerically simulated considering the coupling of eccentricity and density difference. The results showed that the eccentric effect increases with the eccentricity. Further, the fingering trend of high-side displacement interface was enhanced. When the positive density difference increased, the buoyancy effect and consequently the fingering trend of the low-side displacement interface were reinforced. Determining a suitable eccentricity and density difference coupling allowed a critical equilibrium state between the eccentric effect and buoyancy effect. Under these conditions, the displacement interface morphology was relatively stable; the interface length appeared to not significantly increase, and the displacement efficiency reached the maximum value. The simulation results could provide theoretical bases for improving the cement displacement efficiency of horizontal section eccentric annulus.