THE METHOD OF CONTROLLING THE CAVITATION CHARACTERISTICS OF A DRILL JET PUMP

Abstract

The working process of the jet pump is characterized by an increased probability of cavitation in its flowing part, which significantly reduces the efficiency and limits the spread of oil and gas ejection technologies. Based on the use of the equation of energy conservation and flow continuity, a methodology for determining the limiting operating parameters of a downhole jet pump that correspond to cavitation-free operation of the ejection system under the condition of relative rotation of the working medium has been developed. The design scheme of the pressure ejection system is represented by linear hydraulic resistances of the drill string and annulus and local resistances in the form of the working nozzle of the jet pump and the washing nozzles of the bit. Using the system of Bernoulli equations written for the characteristic cross-sections of the ejection system, the correspondence between the minimum pressure value in the flowing part of the jet pump, the depth of the well, the flow rate and the diameter of the working nozzle was established. The relative rotation of the mixed flows was taken into account using the compression ratio of the working flow, the value of which depends on the parameters of the circulation movement of the mixed flows. The minimum pressure value in the flowing part of the jet pump depends directly on the depth of the well and the working flow rate and inversely on the diameter of the working nozzle. The cavitation characteristic of the ejection system is presented in the form of the dependence of the limiting operating parameters on the value of the angle of inclination of the guide elements installed in the flow part of the jet pump. With an increase in the angle of inclination of the guide elements, the minimum diameter of the working nozzle of the jet pump increases. The dependences of the maximum permissible flow rate and the minimum permissible depth of pump placement in the well are characterized by an extreme nonlinear dependence on the angle of inclination of the guide elements.