水力驱动桥塞的计算流体力学分析

CFD Analysis of Water-driving Bridge Plug

桥塞在水平井段受液流冲击驱动,流体对桥塞的作用力大小除了与流量、流体黏度有关外,还受桥塞长度、桥塞-套管间隙等结构尺寸的影响。运用CFD方法数值模拟套管-桥塞结构的流场,确定了不同工况下的液流作用力和驱动压差,得出以下结论：桥塞端面压力远大于壁面切向力,是桥塞运动的主要动力,随着井口注液速度的增加或套管-桥塞间隙的减小,液流作用力显著增大,对电缆的抗拉强度有较高要求,应严格控制流速和环空间隙,当间隙为1.0~1.5 mm时,注入流速应小于1.0 m/s;在驱动桥塞的过程中,注入液的部分压能转化为高速间隙液的动能,由于存在环空间隙的变截面和桥塞相对液流的速度差,流场出现明显涡漩,增大了桥塞两端压差;桥塞下入速度的提高和偏心使得液流作用力下降,根据同心桥塞在低运动速度下的模拟结果选择电缆,可提高其安全性。分析结果为桥塞在水平井段中的封堵设计和应用提供了理论依据。

Bridge plug is impacted and driven by flow fluid in horizontal interval, and the acting force is closely related to the fluid flow and the velocity and size of bridge plug. CFD is used for the numerical simulation of flow field of casing-plug to identify the acting force of flow fluid and driving pressure difference under different working conditions. The following conclusions can be drawn： the pressure on end face is much larger than tangent force on wall of plug; therefore, the pressure on end face is the major driving force; with the increase of injection rate at the wellhead and the decrease of clearance between casing and plug, the acting force of flow fluid increases greatly, which means high demand for tensional strength of wireline; the flow speed and annulus gap shall be strictly controlled; when the gas is 1.0 - 1.5 mm, the injection speed shall he less than 1.0 m/s; in the process of driving bridge plug, a portion of pressure energy of injected fluid will be transformed into kinetic energy of high speed fluid in the gap; due to changing section of annulus and speed difference between plug and flow fluid, the whirl shows up in flow field, increasing the pressure difference between two ends of bridge plug; the speed in- crease of plugging setting and its eccentricity decreases the acting force of flow fluid; wireline should be selected based on the numerical simulation of the concentric plug moving at a low speed, which can improve the safety.