Study On Single Crank And Positive Torque Flexible Pumping System

Artificial lift technology dominates oil production in the world, and the conventionalbeam pumping system is the world’s most widely used artificial lift technology. Theconventional beam pumping system has high energy consumption and low efficiency when itapplies to stripper wells, which is not only inconsistent with the national energy savingrequirements, but also reduces the economic benefits of development. The number of stripperwells increases as many oilfields come into middle and late period and more low productivityand low permeability reservoirs is developed. The problem of beam pumping system is moreserious. In order to solve the problem, the principle of single crank positive torque flexiblepumping unit is developed and the structure of one new pumping unit is designed. The workcharacteristics of hydraulic self-sealing oil well pump and steel wire flexible oil well rod areinvestigated. The low energy consumption and high efficiency pumping system for stripperwells is optimized and designed.In order to solve the negative torque and low efficiency of the conventional beampumping unit, the multi-level phase shift balance positive torque principle and high efficientflexible transmission principle are proposed. The new single crank positive torque flexiblepumping unit is designed based on the principles. Calculation formulas of the hanging pointdisplacement, velocity, acceleration, and the net torque of the output shaft of the reducer ofthe pumping unit are derived. The net torque of pumping unit and the effect of structureparameters on the kinematics and dynamics of the pumping unit are analyzed. The resultsshow that the net torque of the pumping unit is positive and there are different influence onthe kinematics and dynamics of the pumping unit when the structural parameters are different.The conventional plunger pump is replaced by the hydraulic self-sealing pump in orderto reduce the leakoff rate and the friction. The working characteristic of the hydraulicself-sealing pump is studied. According to the structure and working principle of the hydraulicself-sealing pump, fluid pressure variation of the pump is studied. Through laboratoryexperiments, the leakage and friction of the pump are tested. The analysis and test resultsindicate that, in the low-yielding wells, the upstroke fluid pressure can be approximated as aconstant sunk pressure, and the downstroke fluid pressure can be approximated as a constant traveling valve outlet pressure. The results also include that the leakoff rate of the pump isnear to zero, the upstroke friction of the pump remains constant, the downstroke friction ofthe pump is approximately zero, and the leakoff rate and friction are insensible of thevariations in the gap between the plunger and the cylinder.To reduce the conventional sucker rod string weight and eliminate the coupling brokenoff and the piston effect, the wire rope flexible sucker rod string is selected and studied. Basedon the good tensile and no compressive mechanical properties of the wire rope, the heavierrod is installed on the lower part of the wire rope flexible sucker rod. The force acting on thesucker rod string is analyzed, and the mathematical model of the rod string vibration isestablished.According to the mathematical models of work characteristics of the single crankpositive torque flexible pumping unit, the hydraulic self-sealing oil pump and the wire ropeflexible sucker rod string, the mathematical model of work characteristics of the flexiblepumping system is established. Using finite difference method, the model is programmed forsolving. On the basis of a stripper well production condition, the sucker rod string and thepumping unit structure are optimized by the program. In the optimized pumping system, thewire rope is exposed only to the pulling force, and the net torque of the pumping unit reduceroutput shaft is positive and keeps smaller fluctuation range.By use of parametric modeling method in the ANSYS Workbench software,three-dimensional model of the key structure of the single crank positive torque flexiblepumping unit is established. By means of finite element static mechanical analysis, the stressand strain of the key structure with different size parameters are studied. And then the strengthof the key structure is checked to make sure the structure to compliance with the safetyrequirements.On the basis of theoretical studies, the prototype of the single crank positive torqueflexible pumping unit is manufactured. By means of laboratory and field tests, theperformance of the pumping system composed by the unit and the hydraulic self-sealingpump and the wire rope is tested. The indoor test proved that design principle of the unit iscorrect, technically feasible. Field test shows that the pumping system achieves positivetorque with the low rod load, and improves helpful load rate and system efficiency.