水平井偏心环空低速顶替运移机制研究

水平井固井顶替过程中，受限于现场设备，难以实现紊流顶替，而在层流流速区间内，两相流体在偏心环空中运移机制复杂。基于计算流体动力学方法，建立几何模型和数值模型，采用流体体积法对两相流体顶替界面进行追踪，研究了不同顶替流速下水平井偏心环空流体运移机制。结果表明，（1）低偏心度下，1倍隔离液用量能够实现90%顶替效率，而当偏心度大于0.5时，顶替效率相对较低，即使增加隔离液用量，也未能提高顶替效率；（2）针对套管严重偏心情况，将流速由1.0 m/s降低到0.2 m/s，有助于界面平稳发展，并多置换出6.8%钻井液，解决窄边滞留，宽边指进问题；（3）水平井偏心环空固井注替过程存在偏心效应、重力效应、黏滞效应等多方面影响，这些因素相互制约、相互作用，因此，针对现场实际井况，合理设计固井工艺参数，不仅能提高固井质量，还能起到降本增效的作用。

Study of the Transport Mechanism of Low-speed Displacement in Eccentric Annulus of Horizontal Wells

When displacing the cementing of horizontal wells, it is usually difficult to realize the replacement in turbulent flow because of instrumental limitation. In laminar flow, however, the transport mechanism of two-phase flow in the eccentric annulus can be quite complex. Based on the computational fluid dynamics method, we developed a geometric and numerical model, tracked the displacement interface of two-phase flow using the fluid volume method, and analyzed the transport mechanism of displacing fluids in the eccentric annulus of horizontal wells under various displacing flow rates. The following conclusions are drawn from the results:(1) With a low eccentricity, one-time use of isolation fluid can realize 90% displacing efficiency. When the eccentricity is greater than 0.5, the displacing efficiency becomes relatively small. In this case, increasing the amount of isolation fluids cannot further increase the displacing efficiency; (2) Considering the severe eccentricity of the casing, reducing the flow rate from 1.0 m/s to 0.2 m/s can help stabilize the interface and results in 6.8%higher displacement of drilling oil. Furthermore, this approach can also resolve the retention issue on the narrow side and pointing issue on the wide side; (3) The cementing displacement process in the eccentric annulus of horizontal wells is affected by multiple factors, including the eccentric effect, gravity effect, and viscous effect. These factors interact and inhibit with each other. Therefore, a reasonable design of cementing process parameters based on the actual well conditions on site can not only improve cementing quality, but also reduce cost and increase efficiency.