油气井注水泥顶替机理研究进展

Research progress in the cementing displacement mechanism

油气井固井时,保持注水泥顶替界面的稳态,不仅能减少水泥浆对钻井液的污染,而且还可显著改善注水泥顶替效果。目前的注水泥顶替机理研究成果,尚未建立描述在任意井斜角、偏心环空内的注水泥顶替界面变化数学模型,对注水泥顶替设计的实际指导意义不大。为此,在综述影响注水泥顶替效果的主要因素以及注水泥顶替理论研究现状的基础上,重点分析了"平板流模型"和"Hele-Shaw模型"两种理论在顶替机理研究中应用情况。平板流顶替模型将环空中的顶替看作一维轴向顶替,且无法获得顶替界面在环空的整体形态,只适用于直井内的注水泥顶替;Hele-Shaw顶替模型是考虑轴向和周向速度的二维顶替模型,能够追踪顶替界面在环空中发展情况,有利于确定流体之间界面稳定的定量条件。两者相比,Hele-Shaw顶替模型更接近注水泥顶替实际,且不受井斜角的限制。因此,积极开展基于Hele-Shaw模型的注水泥顶替理论研究具有重要的科学意义和应用价值。

In the course of cementing, to keep displacement interface steady can not only prevent cement slurry from being polluted by drilling fluids, but also improve cementing quality remarkably. However, the current research results are of little significance to guide cementing displacement designs in practice because no such mathematical models have yet been established for describing the displacement interface in the eccentric annulus suitable for wellbores with any deviated angle. In view of this, based on the analysis of the existing cement displacement theories as well as the main influencing factors on cementing quality, this paper discusses mainly the foundation of the slot flow model and the Hele-Shaw model and their applications respectively. The slot flow model is only used for cementing displacement in vertical wells because it only regards the displacement in the annular space as one-dimensional axial dis- placement so a full view of displacement interface in the annulus is inaccessible. The Hele-Shaw model holds that the displacement in the annulus is two-dimensional in both axial and circumferential directions, by which states about displacement interface in the annu- lus can be tracked and quantitative conditions on steady interface can be obtained. By comparison, the Hele-Shaw model is closer to the real practice of cementing displacement, especially in horizontal and highly deviated wells. So it is of application value and scien- tific significance to the theoretical research of cementing displacement mechanism based on the Hele-Shaw model.