分支井汇合流动压降计算

随着节约型开发方式的发展以及海洋油气的开发，分支井开发油气资源技术越来越受到人们的重视。分支井开采的一个显著特点是存在分支与主支的汇合，在汇合点处存在汇合流动的局部阻力损失，即汇合流动压降。为此，需要建立汇合流动压降物理及数学流动模型，分析汇合流动局部损失的大小，从而为分支井油气产能分析提供基础。文中采用类比方法建立了三分支井的物理模型；通过流体力学分析，建立了三分支井的等径三通的汇合流动模型和等径斜支管的汇合流动模型；汇合流动压降计算表明，当总的流量小于1000m^3／d，各支管内直径不小于76mm时，无论是等径三通还是等径斜支管，其局部阻力损失都很小，最多为0．01MPa左右，是1000m井深油井重力压力损失的0．13％左右；而在生产压差为6MPa水平段井筒内，局部阻力损失0．01MPa，只有6MPa的0．17％左右。考虑现场的工程实际，可以忽略由于分支汇合流动而造成的局部阻力损失。而且三分支井的分支点处采用普通分叉管时，汇合点处最好采用等径三通连接。

Pressure Drop Calculation for Aggregate Flow in Multilateral Wells

With the improvement of economic development mode and the exploitation of offshore hydrocarbons, more and more attention is paid on the multilateral wells in the development of hydrocarbon resources. A distinguished feature of multilateral-well development mode is the convergence of branches and major branch. The local resistance loss in the intersection point is named as the aggregate flow pressure drop. Therefore, it is necessary to establish the physical and mathematical flow model for the aggregate flow pressure drop, analyze the magnitude of the local resistance, and thereby offer foundations for the productivity analysis when developing oil and gas with multilateral wells. The physical model for three-branched well was established by means of analogy. The aggregate flow models for the equant tee joint of three braches and for the equant oblique branch were established respectively by the analysis of fluid mechanics. Computation results for the aggregate flow pressure drop show that the local resistance loss is negligible for both the equant tee joint and the equant oblique branch when the total flow rate is less than 1000 m3/d and the diameter of each branch is no less than 76mm, the maximum value of which is about 0.01MPa that is about 0.13 percent of the gravitational pressure drop of a well at the depth of 1000m. Simultaneously, the local resistance loss in the bore hole is only 0.17 percent of the horizontal drawdown pressure of 6MPa. In the light of the in-situ engineering practice, the local resistance loss resulted from the multilateral aggregate flow can be negligent. Meanwhile, it is better to use equant tee joint on the intersection point when the normal Y-branch is adopted on the branch point of three-branched well.