RU2380521C2 - Method of oil withdrawal from high gas content well and electroloading equipment for it - Google Patents

Abstract

FIELD: oil-and-gas industry.

SUBSTANCE: descend an assembly into borehole at a defined depth, which includes a centrifugal pump (CP) and a submersible asynchronous motor (SAM).Set up current frequency f_s, feeding SAM, in a range f_s=(0.74-0.78)f, start up SAM, extract a damping fluid from a production string (PS) until dynamic level. After the SAM descending pump compressed inert gas in to the bottomhole clearance. At that control dynamic level with a frequency (4-6) times per hour. Bleed the bottomhole clearance inert gas into a oil collector system with a rate of overburden pressure depression (2-4) at/hour and limit the current value, feeding SAM till a nominal one. At that keeps the mentioned value simultaneously changing current frequency inversely to the current variation value. Also in side of the PS a tubing string located, equipped with CP in its bottom part. SAM stiffly connected to the CP shaft. PS wellhead connected with a tubing system via shut off valve and fitting, and via the second shut off valve and a return valve - with a nipple chamber and oil collector. A sonic depth finder installed on the wellhead fitting for identification of dynamic level current value. A control station installed on the well surface, which includes a frequency converter, connected via transformer, a power cable, equipped with a high temperature cable cover, to the SAM, controller connected with its output through PI regulator to the frequency convector driving port, and with input - to a remote sensing submersible block.

EFFECT: light hydrocarbons with a high content of associated gas extraction assembly operation regime stability increase.

2 cl, 2 dwg

Description

The invention relates to the oil industry and can be used to produce products with high gas content and low density from a well equipped with a submersible electric centrifugal pump unit.

There is a method of selecting oil from wells by selecting the appropriate installation of electric centrifugal pumps (ESP) by calculation, equipped with a gas separator (G.Z. Ibragimov and others. Technique and technology for the extraction and preparation of oil and gas. M: Publishing house MGOU, 2005)

After descent into the well and applying voltage to the ESP electric motor, the well is brought to a stationary mode of operation. At the same time, periodically, using an automated gas metering unit (AGZU), the current value of the pump’s daily output (Qzh) is determined, the current value of the liquid level in the well (Ndin) is determined with the help of an echo sounder, and the value of the annular pressure in the well (Rz) is determined using manometers. Periodically, using a sampling valve installed on the wellhead reinforcement, samples of the well products are taken for the value of its current water cut (V,%). With the help of instruments installed in the control station, the current value of current loads on the electric motor is measured, the “protections” are set, with the deviation from the rated current loads (In) acceptable for the motor: with “overload (ZP)”, referred to as overload protection, and “underload ( ZSP) ”, referred to as“ feed failure protection ”. In the process of bringing the well to a stationary mode of operation, the ESPs are periodically turned off for natural cooling of the electric motor and restoration of the liquid level in the well. The well is considered to be brought to a stationary mode of operation, if during the last 8 hours of continuous operation of the ESP, stabilization of the values of Qzh, Ndin and V.

The disadvantages of this method are that it is unacceptable when developing formations with light hydrocarbons, which are characterized by a high gas content (up to 250 m ³ / t). This is expressed in the fact that when the pressure at the inlet of the electric centrifugal pump decreases, the volume of the gas phase increases several times and the gas separator does not provide the outlet of the incoming gas to the nominal value for the ESP. At the same time, when low-density products (gas-liquid mixture) come from the reservoir, the current loads and, accordingly, the power consumed by the submersible motor are reduced. The current consumption of the motor It decreases to the values of the no-load current Ixx of the motor, i.e. It≈Ixx and the protective block of the ZSP installed in the station turns off the electric motor. ESP, selected by calculation according to well-known methods in wells with high gas content, operates in a periodic (unstable) mode and does not go to a stationary mode of operation. In the case of forced "coarsening" of the ZSP parameters at the control station, the ESP engine in the well "overheats" with a decrease in the insulation resistance of the stator windings and fails.

The closest analogue is the method of oil extraction from wells by an installation including an electric centrifugal pump driven by a submersible induction motor (Patent RU 2016252, IPC F04D 15/00, publ. July 15, 1994), which includes measuring and maintaining pressure values at the centrifugal pump intake , measuring the active power and operating current of the motor, calculating the energy coefficient and regulating the speed of rotation of the pump drive by changing the frequency of the current supplying the submersible asynchronous electric motor.

This patent describes an installation for implementing the known method of pumping oil, which contains a production casing, a submersible induction motor, which drives an electric submersible centrifugal pump (ESP), and tubing. The submersible induction motor is powered from the power transformer through the control station via a power cable. Manometers were used to measure pressure in the annulus, at the mouth and to control the flow line. The flow control is provided by a fitting, and the prevention of fluid drainage from the flow line into the annulus of the well and overflow relief is provided by a check valve.

The disadvantages of the known method and installation are: the need for additional testing at the stand of each section of the installation, followed by calculations of the energy coefficient; the lack of technical equipment (stands) and appropriate methods for assessing the active power consumption of ESPs when pumping liquid media with a large (> 70%) volumetric gas content; a significant difference between the energy coefficient installed on water and the energy coefficient obtained for gas-liquid media and, therefore, the inability to achieve stable operation of the installation that implements the above method.

The technical result of the invention is to increase the stability of the operating mode of the installation in the well, pumping light hydrocarbons with a high content of associated gas.

The specified technical result is achieved by the fact that in the method of pumping oil with a high value of associated gas, an installation including an electric centrifugal pump, a submersible induction motor is lowered into the well to a predetermined depth, the frequency f _{p of the} current supplying the submersible induction motor is set within f _p = ( 0.74-0.78) f, start the submersible induction motor, driving the pump, pump out the kill fluid from the production string to a dynamic level, after starting the submersible asynchronous electric motor compressed inert gas is pumped into the annulus of the well, while the dynamic level of the well is monitored at a frequency of (4-6) times per hour, from the moment the formation production arrives in the oil gathering system, inert gas is drained from the annulus into the oil gathering system with a rate of excess reduction pressure (2-4) at / h and limit the amount of current supplying the submersible induction motor to the nominal value, maintaining the indicated value while changing the frequency of the current back to ortsionalno change in the value of current powering the submersible induction motor.

An installation for pumping oil with a high value of associated gas from a well contains a production string, inside of which there is a tubing with a centrifugal pump located in its lower part, with a submersible asynchronous motor rigidly connected to its shaft, the wellhead of the column through the first valve and the pipe connection located on the surface of the well pump-compressor unit for the injection of inert gas, and through the second valve, check valve - with the unit choke chamber and the system eftesborder, sonar to determine the current value of the dynamic level, located on the wellhead reinforcement, a control station installed on the surface of the well, including a frequency converter connected via a transformer, a power cable equipped with a high-temperature cable insert, with a submersible asynchronous electric motor, a controller, an output connected through PI controller to the control input of the frequency converter, and the input to the submersible telemetry unit mounted on the submersible asynchronous electric trodvigatele.

Figure 1 presents a diagram of a well equipped with a unit for pumping oil with high gas content from the well.

Figure 2 is a block diagram of a control station.

Installation for pumping oil with high gas content from the well contains a reservoir 1 (Fig. 1), production casing 2, inside of which there is a tubing 3 with a centrifugal pump 4 located in its lower part, with a shaft of which a submersible asynchronous electric motor 5 is rigidly connected The wellhead of the column through the first valve 6 and pipe 7 is connected to a pump-compressor unit located on the well surface (not shown in the drawing) for inert gas injection, and through the second valve 8, ny valve 9 - choke assembly with the chamber 10 and oil collection system (not indicated by the figure). Gate valves 6 and 8 are designed to open and close the annulus of the well. To determine the current value of the dynamic level, an acoustic echo sounder 11 was used, and to control the magnitude of the annular pressure, a manometer 12 was used, which was placed on the reinforcement of the wellhead. A control station 13 (FIG. 2) is installed on the surface of the well, including a frequency converter 14 connected through a step-up transformer 15, a power cable 16 (FIG. 1), equipped with a high-temperature cable insert 17, with a submersible asynchronous electric motor 5. The control station is equipped with a controller 18 (figure 2), the output connected through the PI controller 19 to the control input of the frequency converter 14, and the input to the submersible telemetry unit 20 mounted on a submersible asynchronous electric motor 5.

The power P _{dv of a} submersible induction motor is selected taking into account the following relations:

where Q _W - the potential flow rate of the well in liquid, m ³ / day;

N _in - the depth of the descent of the pump unit into the well vertically, m;

γ _W = 0.35 - the density of the gas-liquid mixture at the installation;

η is the efficiency of the pump,%.

The nominal productivity Q _{n of a} centrifugal pump is determined from the relation Q _n = k · Q _w , where k = 3 ÷ 4 is the fill factor of the pump cavity with gas, and for lifting the gas-liquid mixture from the well, the number of working steps Np in the pump is established from the ratio Нр = Н _в / h _sec

High temperature cable insert 17 at the bottom of the power cable 16 resists temperatures up to 230 ° C and has _a length L defined _in relation L = 0.5H _to -1000, where _L> 0, m.

The controller 18 in the control station 13 performs the functions of manually entering and subsequently storing the specified parameters of the “settings” of the protections and monitoring the operation of the electric motor 5, with the issuance of information on the display panel of the controller. The controller contains a summing block (not shown in Fig. 2), whose functions include estimating the level of mismatch of the controlled parameters (temperature, pressure, current, etc.) from the set value and issuing control signals (commands) to eliminate this mismatch (approximation to zero).

The frequency converter (IF) 14 is designed to control the output frequency for the pump motor. The transformer 15 is necessary to increase the output voltage with a modified output frequency at the output of the inverter 14 to the voltage necessary for the normal operation of the submersible motor.

An asynchronous submersible motor with its shaft is connected via a spline connection to the pump shaft and performs the function of its drive. By changing the frequency of the current supplied from the control station, the motor shaft can change the rotation frequency in the range of ± 25% of the value of the industrial frequency of the current and, accordingly, increase or decrease the pump capacity and its pressure.

The submersible telemetry unit 20 is intended for measuring and transmitting along the copper conductors of the power cable to the controller 18 information about the temperature and pressure in the electric motor 5, as well as the level of mechanical vibrations of the electric motor housing.

When this block diagram is in operation, the output current of the inverter 15 is constantly measured and compared with the set current value in the PI controller 20. When the current loads are mismatched> 3%, the PI controller 20 instructs the controller 19 to generate an IF 15 command to increase or decrease current frequency.

Using wellhead valves (gate valves, pressure gauges, adjustable fittings located in the fitting chamber), manual control of the operation of the well is carried out. The check valve 14 provides relief of excess pressure of associated gas in the well.

To control the operation of the ESP (start, stop, operation of the ESP at predetermined time intervals, changing the frequency of the supply current, performing monitoring functions with recording the current operating parameters, protection against unacceptable changes in the technological parameters of the motor, pump and cable), the ground control station is used.

To control the temperature in the engine, the pressure at the pump intake and the vibration level, a telemetry immersion unit 20 is used.

The method of pumping oil from the well using the described installation is as follows.

For the operation of productive formation 1, an electric submersible installation (ESP) is lowered into a “muffled” oil well to the estimated depth of descent Nsp, for example, to a depth spaced 50-100 m above the top of the productive horizon. The production of formation 1 enters production casing 2 after creating a depression on the reservoir. This condition begins to be satisfied after pumping out the killing fluid from the production string and lowering the level in the well to Nd. At the same time, the developed head (Well) of the ESP should be sufficient so that from a given depth determined by the sum of the dynamic level (Nd) and the depth below the level (Nz), the well production rises to the wellhead and is fed into the oil gathering system, overcoming the hydraulic resistance in the pump compressor pipes and internal pressure in the oil manifold.

The centrifugal pump is started after the frequency fp of the current supplying the submersible asynchronous electric motor is established at the control station, taking into account the ratio f _p = (0.74-0.78) · f, where f is the value of the industrial current frequency. At an industrial frequency of 50 Hz, the frequency of the supply current f _p = (37 ÷ 39) Hz).

When pumping out killing fluid from the well, the density of which when entering the mode exceeds 1 g / cm ³ , to the calculated dynamic level (Nd) the maximum power of the SEM is required. In the proposed method, to compensate for the deficit in the power installed for the SEM and increase the hydraulic head at the ESP output after starting the electric motor in the annulus of the well through the nozzle 7 and the open valve 6, compressed inert gas is pumped. The calculated value of the pressure in the annulus is determined taking into account the accepted dependence, including the current value of the dynamic level in the well (Nd). The dynamic level of the well is determined by an acoustic echo sounder 12 with a frequency of (4 ÷ 6) times per hour. After the production of formation 1, the density of which is several times lower than the kill fluid, enters the well, the power consumption of the PEM will automatically decrease in proportion to the decrease in the density of the pumped gas-liquid mixture. Upon receipt at the pump intake of a gas-liquid mixture with a density of 0.25-0.35 g / cm ³ (set according to the results of wellhead samples of production from the well), the pressure in the annulus of the well is forcibly reduced by releasing gas through a valve 8 into the oil recovery system. After the formation products enter the electric centrifugal pump, the current frequency is increased at a rate of (0.2-0.3) Hz per hour until it is aligned with the industrial frequency value. After that, the control station includes a system for automatically controlling the mode of limiting the current consumption of a submersible electric motor (SEM), the value of which is taken from the passport characteristics of the SEM as the value of the nominal current of the SEM (I _nom ). Using this function integrated in the control system, the nominal current of the PED is automatically maintained, while the current frequency is changed inversely with the current: with an increase in the load of the PED, that is, with an increase in the current, the output frequency decreases, and when the load decreases, that is, when the load decreases current magnitude, current output frequency increases).

Placing in the lower part of the cable line a high-temperature insert 17 with a length of 200-300 m allows you to completely eliminate the temperature effect of the motor and pump on the lower part of the cable during the output of the well to the regime and the deficiency of coolant associated with this process.

When using the traditional approach to the operation of ESP wells, including the method described in the closest in technical essence analogue, it is not possible to obtain stable ESP operation for oil reservoirs with high gas content. The energy power factor obtained at the stand for the analogue is determined using an aqueous medium. Under real operating conditions of oil wells with high gas content, it is much less, because low-density gas-liquid mixture is pumped. It should be noted that in the current operating conditions of oil fields it is not enough to optimize the operation of only the well and the ESP, as this is solved in the above analogues and prototype. The operation of the reservoir-well-pump system should be optimized taking into account the hydrodynamic characteristics and physical properties of the formation fluid, in particular density and gas content, gas saturation pressure of oil, and reservoir temperature.

Thus, the invention allows, in comparison with the known, to increase the stability of the electric submersible installation in wells with high gas content since aimed at preventing conditions for disruption of the pump supply, overheating of the motor and cable in the lower part of the cable line and increasing the time between failures of the whole installation.

Compared with the known methods for selecting the power of the SEM, the proposed ratio for choosing the power of the electric motor gives about 2.5-3 times less power.

The method for pumping oil with high gas content from the wells and the electric submersible installation allow the well to enter a stable mode for a long period, which is limited by the service life of the wearing parts of the installation (support textolite washers, radial and axial bearings, impellers of the pump), to optimize the selection of products from the well, increase MTBF.

Claims (2)

1. The method of pumping oil with a high value of associated gas from the well, which consists in letting the unit down, including the electric centrifugal pump, the submersible induction motor, set the frequency f _{n of the} current supplying the submersible asynchronous motor within f _p = ( 0.74-0.78) f, where f is the value of the industrial frequency of the current, start the submersible induction motor, driving the pump, pump out the kill fluid from the production string to a dynamic level, after starting the submersible a a synchronous electric motor, compressed inert gas is pumped into the annulus of the well, while the dynamic level of the well is monitored at a frequency of (4-6) times per hour, from the moment the formation production arrives in the oil gathering system, inert gas from the annulus is discharged into the oil gathering system with a decrease in excess pressure (2-4) at / h and limit the magnitude of the current supplying the submersible induction motor at the level of the nominal value, maintaining the indicated value with a simultaneous change in the frequency The current output is inversely proportional to the change in the magnitude of the current supplying the submersible induction motor. 2. Installation for pumping from a well oil with a high value of associated gas, containing a production string, inside which there is a tubing with a centrifugal pump located in its lower part, with a shaft of which a submersible asynchronous electric motor is rigidly connected, the wellhead of the column through the first valve and the nozzle is connected to a pump-compressor unit for pumping inert gas located on the surface of the well, and through a second valve, a check valve, to the assembly of the nozzle chamber and systems oil gathering, sonar to determine the current value of the dynamic level, located on the wellhead reinforcement, a control station installed on the surface of the well, including a frequency converter connected via a transformer, a power cable equipped with a high-temperature cable insert, with a submersible induction motor, a controller, an output connected through the PI controller to the control input of the frequency converter, and the input to the submersible telemetry unit installed on the submersible asynchronous electric ktrodvigatele.

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