REVIEW AND CRITICAL ANALYSIS OF THE CURRENT STATE AND WAYS TO IMPROVE REGULATED POWER SUPPLIES AND AUTOMATIC CONTROL SYSTEMS FOR ELECTRIC CENTRIFUGAL PUMPING UNITS IN INTERMITTENT OPERATION OF OIL WELLS

Abstract

Link for citation: Kladiev S.N. Review and critical analysis of the current state and ways to improve regulated power supplies and automatic control systems for electric centrifugal pumping units in intermittent operation of oil wells. Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 9, рр. 203-215. In Rus. Relevance. At present efforts are being made to convert low- and medium-flow oil wells to cyclical or short-term operation in order to reduce the excess pumping capacity that resulted from the reduction of well flow that is caused by reduced reservoir pressure during long-lasting exploitation of the deposit. The need for such a conversion requires justification for the use of more complex configurations of regulated power supply sources and automatic control systems of centrifugal pump units electric drives in automated process control systems. The local low-level automatic control systems for a mechanized electric drive method for lifting an oil-containing liquid from the well to the surface, namely the installation of variable-speed AC electric drives consist of ground-based devices and special submersible equipment. The ground-based devices are control stations with AC voltage and frequency converters with built-in telemetry units, external sine filter, step-up transformer. The special submersible equipment includes asynchronous induction electric motor, power cable, submersible telemetry unit, process sensors, centrifugal pump. The power supply of such a unit is provided from the external electric three-phase network of 6 kV through a reducing transformer substation of 6/0,4 kV. In the continuous mode of operation of oil pumping plants the electric pumps and other equipment, operate in quasi-static modes. Unregulated electric drive, as well as the open-loop controlled electric drive does not allow for smooth acceleration to the nominal performance of pumping equipment for pumping oil out of well in difficult conditions and its smooth regulation when reducing the well flow because of reducing oil flow to the slaughter. Therefore, the main way of smoothly reducing the excess performance of the submersible centrifugal pump is the periodic activation mode, which includes pumping the oil mixture out of the well and stop – for its accumulation and recovery of formation pressure. The introduction of cyclical technology shows that it is impossible to use the open-loop system of regulated electric drive everywhere, where acceptable quality indicators of transition comparable with the quality of closed-loop control systems are objectively unattainable. Due to the fact that the amount of pressure at the well intake created by a centrifugal pump, necessary to lift the well fluid to the surface, depends on the square of the rotation speed of the pump working stages, the operating pump productivity range Qmin... Qmax (m3/day) is obtained by varying the motor stator winding voltage (80…100) % from the nominal voltage value by using AC voltage controller with a phase control mode. If the stator voltage value is less than 80 % of Unom then the well fluid is not lifted to the surface and does not flow out of wellhead equipment. Therefore, when a frequency converter with Unom/fnom=const is used, the supply voltage and frequency of the motor should be varied in the same range. The price for using cyclic operation is a decrease in the reliability of submersible pumps. It is necessary to use special designs of submersible electric motors, improve power supply systems and synthesize closed-loop control systems of automatic control of electric drive of submersible pump. The purpose of the study is the review and critical analysis of the current state and ways to improve regulated power supplies and automatic control systems for electric centrifugal pumping units in intermittent operation of oil wells. Object: systems of power supply and automatic control of centrifugal pump units in intermittent operation of oil well, telemetry systems, energy-efficient submersible motors and centrifugal pump designs. Methods: methods of the theory of the automatic control system for developing the concept of operation of low flow of wells, analysis and synthesis of open and closed loop control systems of electric submersible centrifugal pumping units. Results. The paper introduces the scientific problem of development, implementation, models and methods of identification of technological processes, complexes and integrated control systems of oil extraction by electric drive method, taking into account the influence of a long submerged cable, low flow of wells and difficult operating conditions. The author proposed scientifically based technical solutions in the form of a structure of a power channel of an electromechanical system with a frequency-regulated induction motor, long submersible cable and indirect method of measuring state variable from ground-based measurements at load changes and measurement channel characteristics.