RU2057907C1 - Process of exploitation of low-discharge well with electric pump having frequency-controlled drive - Google Patents

Abstract

FIELD: oil production. SUBSTANCE: for prevention of influence of drain of fluid from pipe string on discharge of well, for expansion of capabilities of control over inflow of products after termination of pump feed in each cycle frequency of voltage supplied to electric pump is controlled keeping maximal frequency of voltage supplied to electric pump in process of inflow of fluid from pool. Pump does not resume feed to prevent discharge of fluid from string of lifting pipes through pump into well at this frequency and resumes feed with its transfer to increased frequency when pressure at pump intake reaches specified value in process of inflow. EFFECT: improved operational stability of electric pump. 3 dwg

Description

 The invention relates to oil production and can be used for the operation of low-production wells equipped with electric pumps, in particular submersible centrifugal electric pumps.

A known method of operating a low-rate well with an electric pump, based on its periodic operation with turning off the drive motor at a given value of pressure at the pump intake and subsequent start-up after the set technological break for the well has expired [1]
A characteristic feature of this method is the limited regulation of the pump performance by changing the back pressure at the wellhead and the difficulty of setting the duration of the technological pause during which the fluid is drained from the riser pipes into the well and the formation fluid is restored, which does not effectively control the well operating conditions.

The closest in combination of features and technical nature to the proposed invention is a method of operating a low-flow well electric pump with a variable frequency drive, based on the regulation of the rate of fluid flow from the formation into the well by periodically repeating cycles, each of which consists of sequentially carried out processes of starting the pump with increasing the frequency of the supply voltage, the fluid supply by the pump to the column of lifting pipes at a higher than nominal value to reduce the frequency and supply pump zero by lowering the frequency of the supply voltage after reaching a predetermined pressure in the tubing string, followed by disconnecting the pump and the discharge of fluid from the tubing string into the well through a pump [2]
The disadvantage of this method is to limit the flow of fluid from the reservoir into the well as a result of the systematic discharge of fluid from the column of lifting pipes and the uncontrolled recovery process in the well after the pump is stopped.

 The task to which the claimed invention is directed is due to a feature of operating a low-production well whose productivity is small and goes beyond the scope of matching with an electric pump. Therefore, the pumping of fluid from such a well has to be periodically stopped with the aim of the necessary accumulation of fluid in the well due to the influx of reservoir products, however, when implementing the known methods, the recovery process occurs in the well when the pump is disconnected from the power supply, the fluid located in the column of lifting pipes under excess pressure merges into the well and this process cannot be prevented by known methods, including, for example, using deep check valves, Installed on the electric pump. As a result, the efficiency of fluid pumping is reduced, the recovery process is distorted, the flow of fluid from the reservoir is reduced due to the outflow of fluid from the riser pipes into the well. At the same time, starting the pump before the discharge is complete is difficult and can lead to a failure of the pump unit, and a forced increase in the duration of shutdown of the pump is not effective due to a decrease in the influx of formation products. The way out of this situation does not allow the implementation of well-known technical solutions.

 In essence, the proposed method of operating a low-flow well of an electric pump with a variable frequency drive is based on controlling the rate of fluid flow from the formation into the well by periodically repeating cycles, each of which consists of sequentially carried out processes of starting the pump with an increasing frequency of the supply voltage, pumping the fluid into the column lifting pipes at an increased frequency compared to the nominal value and reducing the pump flow to zero by lowering the frequencies supply voltage after reaching a predetermined pressure in the column of lifting pipes with subsequent shutdown of the pump and draining the liquid from the column of lifting pipes through the pump into the well and differs from the prototype in that when the pump is stopped in the cycle, the liquid is drained from the column of lifting pipes through the pump into the well by regulating the pressure developed by the pump at zero supply by changing the frequency of the supply voltage in accordance with the restoration of pressure in the well and in the column of lifting pipes, box under the influence of fluid flow from the reservoir. Resume the pump in the cycle by transferring it to an increased frequency after a given recovery due to the influx of reservoir products, but no later than the expiration of the specified pump operation time in zero flow mode. Regulate the frequency of the voltage during the recovery process in the cycle from the condition of maintaining the highest frequency at which the pump still does not resume the flow of fluid.

 In FIG. 1 shows a installation diagram of a pump with a variable frequency drive, with which a method of operating a well 1 is carried out. The installation comprises a downhole pump 2 on a column 3 of lifting pipes, a drive motor 4 with a current-carrying electric cable 5, a thyristor frequency converter 6, a control device 7, a sensor 8 the pressure in the column of the lifting pipes, the sensor 9 of the frequency of the output voltage of the converter 6, the sensor 10 controls the power consumed by the electric motor 4, the sensor 11 of the voltage of the electric pump in turbine mode rotation, the sensor 12 pressure in the well at a depth of descent of the pump 2 and the sensor 13 of the temperature of the electric motor 4.

 Figure 2 presents a block diagram of an algorithm for implementing the method.

левая область срыва (ЛОС) подачи насоса при работе на газожидкостных смесях (неустойчивость при малой подаче);

правая область срыва (ПОС) подачи насоса при работе на газожидкостных смесях (неустойчивость при больших подачах); →_→_→- траектория рабочего режима насоса при осуществлении способа.In FIG. Figure 3 presents the generalized characteristics of a centrifugal pump with highlighted areas of supply disruption, trajectories of movement of the operating mode according to the algorithm, where

left stall area (VOC) of the pump supply when working on gas-liquid mixtures (instability at low flow);

the right stall area (PIC) of the pump supply when working on gas-liquid mixtures (instability at high flows); → _ → _ → - the trajectory of the operating mode of the pump during the implementation of the method.

 The method is carried out according to the algorithm presented in figure 2, as follows.

• P_нас•(0,198-0,18B) где μ_нд вязкость дегазированной нефти, мПа· с;
μ_нп- вязкость нефти в пластовых условиях, мПа· с,
Р_нас. давление насыщения, МПа,
В обводненность пластовой продукции,
уменьшают до нуля подачу насоса путем снижения частоты питающего напряжения (указание 8, условие 7 на фиг.2, траектория 3 на фиг.3) со скоростью -df/dt, до 1-5 Гц/с. Регистрируют прекращение подачи насоса, например, с помощью датчика частоты 9 и датчика 10 мощности в момент, когда мощность, потребляемая электронасосом на заданной частоте, становится равной потребляемой мощности насоса в режиме нулевой подачи для этой же частоты, определенной по стендовым характеристикам (условие 7 на фиг.2).Using the frequency converter 6 include (indication 1 in FIG. 2) a drive motor 4 via an electric cable 5 to the voltage of the starting frequency f _start (Fig. 2,3) to 10-20 Hz; after that, the electric pump 2 is started for several seconds at an increasing frequency of the supply voltage with a speed of + df / dt, up to 10 Hz (note 2, condition 2 in FIG. 2; path 1 in FIG. 3) to a given frequency, f _ass . increased in comparison with the nominal value of f _n and sufficient for the pump 2 to exit from the left supply stall area [4] while ensuring stable operation in the mode of pumping fluid from the well 1 (indication 3, 4, 5 in FIG. 2, trajectory 2 in FIG. 3). After creating a predetermined pressure P _to P _back in the column 3 of the lifting pipes controlled by the sensor 8, during the operation of the pump 2 at a given frequency, the pressure P _c in the well 1 is controlled, for example, at the depth of the pump descent according to the readings of the pressure sensor 12 of the thermomanometric system after reaching a predetermined pressure value (condition 6 in FIG. 2), corresponding, for example, to that admitted on receiving an electric pump:
P _c = P _add =

• P _us • (0,198-0,18B) where μ _nd viscosity of degassed oil, MPa · s;
μ _np - oil viscosity in reservoir conditions, MPa · s,
P _us. saturation pressure, MPa,
In water cut formation,
reduce the pump flow to zero by reducing the frequency of the supply voltage (reference 8, condition 7 in FIG. 2, trajectory 3 in FIG. 3) at a speed of -df / dt, to 1-5 Hz / s. The cessation of pump supply is recorded, for example, using a frequency sensor 9 and a power sensor 10 at a time when the power consumed by the electric pump at a given frequency becomes equal to the power consumption of the pump in zero-feed mode for the same frequency determined by bench characteristics (condition 7 on figure 2).

 Then, the pump is left to work at the achieved frequency of the supply voltage, providing the necessary pressure to prevent the discharge of fluid into the well 1. In this case, the well is transferred from the pumping mode to the recovery mode carried out under the influence of fluid inflow from the reservoir (due to the exclusion of fluid drain from the riser pipes). In the recovery process (cycle as directed by 8, conditions 7, 9, 10 in FIG. 2; trajectory 4 in FIG. 3), the liquid level and pressure rise in the well, therefore, to keep the pump in zero flow mode (with a pressure sufficient for prevention of fluid drainage from the column of lifting pipes into the well) during the recovery process using the control device 7 systematically change the frequency of the output voltage of the transducer 6 (reference 8, conditions 7, 9, 10 in Fig. 2), maintaining its greatest value at each moment of recovery, at which the pump still does not resume flow (does not leave the VOC) and as a result develops a pressure sufficient to prevent the discharge of fluid from the riser pipes into the well.

• P_нас•(0,325-0,316)•B
Для этого увеличивают частоту питающего напряжения (в соответствии с указанием 2 до выполнения условия 3 на фиг.2, траектория 5 на фиг.3) и далее, регулируют скорость притока жидкости из пласта периодическим повторением процессов откачки и восстановления в скважине, не допуская слива жидкости из колонны подъемных труб. Продолжительность процесса восстановления (условие 9 на фиг.2) без отключения насоса устанавливают индивидуально для скважины из условий, например, охлаждения двигателя 4 в потоке жидкости, создаваемом притоком ее из пласта в процессе восстановления (до нескольких минут). Режим откачки жидкости из скважины устанавливают, в дополнение к приведенным выше условиям, с учетом замены жидкости в скважине до глубины спуска двигателя 4 и насоса 2 и устойчивой подачи без срыва в ПОС, обусловленной снижением гидравлического КПД насоса.The well is transferred from the recovery mode to the pumping mode when, for example (condition 10 in FIG. 2), the pressure at the pump intake reaches the optimum value:
P _c = P _opt =

• P _us • (0.325-0.316) • B
To do this, increase the frequency of the supply voltage (in accordance with instruction 2 until condition 3 in FIG. 2 is fulfilled, trajectory 5 in FIG. 3) and then regulate the rate of fluid flow from the formation by periodic repetition of pumping and recovery processes in the well, preventing fluid from draining from a column of lifting pipes. The duration of the recovery process (condition 9 in FIG. 2) without shutting down the pump is set individually for the well from conditions, for example, cooling of engine 4 in a fluid stream created by its influx from the formation during recovery (up to several minutes). The mode of pumping fluid from the well is set, in addition to the above conditions, taking into account the replacement of fluid in the well to the depth of descent of the engine 4 and pump 2 and a stable supply without interruption in the PIC due to a decrease in the hydraulic efficiency of the pump.

After a given restoration of pressure in the well, but no later than the expiration of a given duration t _in t _ass. the pump operates in zero flow mode, returns to the pumping liquid (note 2 in figure 2), the frequency range in this case is from 40 to 65 Hz. Note that the signal from the temperature sensor 13 t $\genfrac{}{}{0ex}{}{\text{about}}{\text{from}}$ = t $\genfrac{}{}{0ex}{}{\text{about}}{\text{ass}}$ as part of a thermomanometric system, the pump can be turned off. In this case, the well is left for a long recovery (indication 12, 13, condition 11, 14, 15 of the correction of the task of the technological parameters in FIG. 2), the duration of which is determined by the rate of fluid discharge into the well and its effect on the rate of influx into the well from the reservoir. The intensity of fluid discharge from the column of lifting pipes through the pump into the well is determined by monitoring with the help of the sensor 11 the voltage U _g generated by the drive 4.

 Thus, the present invention expands the possibilities of regulating the influx of reservoir products; prevents the limiting effect on the flow rate of a well from the discharge of fluid from a column of lifting pipes; reduces the frequency of repeated starts of the electric pump, which are difficult, even with the frequency control of the electric pump.

Claims (1)

 METHOD FOR OPERATING A SMALL-DEVELOPING ELECTRIC PUMP WELL WITH A FREQUENCY-REGULATED DRIVE, including periodic repetition of cycles, in each of which the pump is started at an increasing frequency of the supply voltage, the liquid is pumped into the column of lifting pipes when the pressure reaches a higher value than the nominal value and in the pipe string, the pump flow is reduced to zero by reducing the frequency of the supply voltage to ensure the flow of fluid from the reservoir, characterized in that after the pump stops flowing in each cycle, the frequency of the voltage supplying the electric pump is regulated, maintaining the maximum frequency of the voltage supplying the pump during the flow of fluid from the reservoir, at which the pump does not resume flowing to prevent drainage of the liquid from the column of lifting pipes through the pump into the well, and resumption of flow by transferring it to an increased frequency, an electric pump is carried out after reaching a predetermined pressure at the pump inlet during the inflow.

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