Optimization of geometry parameters with separation efficiency and flow split ratio for downhole oil-water hydrocyclone

Abstract

High water cut of crude oil has already become a serious problem for earlier oil well, and downhole oil-water hydrocyclone is thought as one of the solutions to solve this problem. But high separation efficiency usually accompanies with big flow split ratio which still costs large efforts to treat it. In this work, research was carried out to detect the effects of geometry factors on separation efficiency and flow split ratio to optimize the geometry. The oil-water two-phase flow in two-cone hydrocyclone was seriously analyzed and a mathematic model was built to describe it. Results show that backflow generates in upper cone and lower cone, therefore the evaluation and optimization are focused on upper cone, lower cone and lower cylinder. First, cases were designed using orthogonal analysis to overcome the interaction of different factors with constant length of lower cone. The angle of lower cone should be bigger than 0.5° and smaller than 3.0° to obtained a high efficiency with suitable flow split ratio. The change of angle of lower cone alters the critical diameter and affects the velocity and backflow in upper cone. Then, simulations were carried out with constant critical diameter to eliminate this influence to further detect their effects on separation and optimize the geometry. The differences of separation efficiencies are all within 1% with same critical diameter, but effects on flow split ratio are much obvious. The optimization of geometry should be focused on flow split ratio, and the promotion of separation efficiency should be focused on determine the relationship between critical diameter and flow rate. The optimal values are recommended for angle of upper cone, angle of lower cone and length of lower cylinder with critical diameter 28 mm.