Technology for Controlling Eccentric Wear of Sucker Rods and Tubing in Pumping Wells Lifting Fluids Containing Polymer

Abstract

Abstract In Daqing Oil Field, after polymer flooding, severe eccentric wear of sucker rods and tubing in many wells with pumping units have occurred. The life span of the tubing string has decreased from 750 days for lifting fluid that does not contain polymer to 270 days for fluid that contains polymer. This has greatly increased work-over job frequencies and the production cost, and has seriously affected normal crude oil production. With respect to this problem, this paper gives an introduction to a technology to control eccentric wear of sucker rods and tubing in pumping wells lifting fluid containing polymer. Based on visco-elastic fluid dynamics, the constitutive equation of visco-elastic fluid and its flowing equation in an eccentric annulus is established, the magnitude of the normal force caused by the flow of fluid containing polymer on the sucker rods and pump barrel is derived and calculated. Based on lab experiments with visco-elastic fluid flowing in the annulus formed by the tubing and sucker rod, the relationship between the magnitude of the normal force of flowing viscoelastic fluid with different concentration, velocity and eccentricity of the sucker rod related to the tubing is measured; the resistant force of visco-elastic fluid flowing across pump valves and pump barrels is also measured; it could be seen (both visually and numerically) that the eccentric wear is mainly caused by the normal force of the flowing visco-elastic fluid. On the basis of the above study, measures to prevent eccentric wear were implemented, which includes centralizing sucker rods, using large clearance pumps with large channels, using uniform diameter sucker rods in the whole well-bore and regularly rotating the sucker rod string. Practice on 6,266 wells in the field indicates that these measures can effectively solve the problem of eccentric wear of sucker rods and tubing in pumping wells, the life span of the tubing string increased from 270 days to more than 1,000 days, which brought about marked economic benefits. At present, all pumping wells in Daqing that lift fluid containing polymer use the technology described in this paper.