RU2573613C1 - Downhole electrically-driven rotary pump unit protection - Google Patents

Abstract

FIELD: engines and pumps.

SUBSTANCE: claimed process consists in interruption of pump motor supply at the depth telemetry transducer reading equal to or lower than the preset magnitude. One pressure transducer is fitted at the pump intake while the second pressure transducer is arranged in tube space at the wellhead. Transducer pressure P_min whereat and below which the pump motor operation is interrupted and it is continuously calculated as the sum of two pressures, i.e. liquid column pressure P_hydro above the transducer and gas pressure above the gas-fluid interface (dynamic level) P_GFI: P_min = P_hydro+P_GFI. Note here that P_GFI is defined by calculation proceeding from the readings of the second wellhead pressure transducer while P_hydro is set constant proceeding from the in-well conditions and downhole pump performances.

EFFECT: higher efficiency of protection.

1 dwg, 1 tbl

Description

The claimed invention relates to the theory and practice of operating oil wells using deep pumping equipment and can be used in the oil industry.

Installations of electric centrifugal pumps (ESP) in many oil producing enterprises ensure the formation of the main or significant share of the oil produced, therefore, due attention is paid to the safety of their operation. At present, ESPs are often equipped with in-depth telemetry in the form of a TMS thermomanometric system (p. 276 of the textbook: Borehole Oil Production / MM Kabirov, Sh.A. Gafarov. - St. Petersburg: Nedra LLC, 2010. - 416 p. ) TMS disconnects the submersible electric motor (SEM) from the power supply when the pressure of the medium around the SEM is lower than the set minimum value (page 22 of the training manual: Zeygman Yu.V., Gumerov OA. Operational efficiency of electric centrifugal pump installations in wells. - Ufa .: OOO "Monograph", 2006. - 88 p.).

In an oil well, the annulus between the lift pipe casing and the casing is usually filled with two media: gas (associated petroleum gas) and liquid with a certain dissolved gas content. Based on this existing situation, the pressure of the medium around the SEM is the sum of two components: the pressure on the gas-liquid section of the WLW and the pressure of the liquid column with dissolved gas from the gas-liquid section to the submersible motor:

The existing protection system for a submersible electric motor and deep ESP is based on measuring pressure in the SEM zone, which, according to formula (1), can be created in three ways.

1. Above the PED in the annulus is the borehole product in the form of oil or emulsion with a certain content of dissolved and free gas. Above this column of liquid there is associated petroleum gas under a certain pressure Р _ГЖР .

2. The pressure of associated petroleum gas (APG) may be absent in the well: P _GZHR = 0. This situation can be seen with the open valve of the annulus or with the constant pumping of APG from the annulus using the wellhead compressor.

3. Under certain conditions, the height of the liquid column in the annulus may decrease to a minimum value equal to the distance from the entrance to the ESP to the sensors of the thermomanometric system. Such a situation leads to free gas entering the ESP turbines and interruption in the supply of well products by the downhole pump. In this unfavorable situation, the pressure in the TMS zone may be higher than the minimum pressure value P _min at which the submersible motor is switched off. This is possible with high pressure associated petroleum gas in the annulus.

Consider an example. In the well with ESP and TMS, the following value of the minimum allowable pressure P _min = 2.0 MPa was established. At a certain point in time, the ESP pumps out the borehole production in the liquid phase from the annulus, and the dynamic level descends to the reception of the electric centrifugal pump. An emergency occurs with the subsequent destruction of the SEM or ESP. In this case, the TMS pressure sensor located in the lower part of the SEM shows a pressure higher than P _min , and the SEM does not disconnect from the power supply. Such a picture is possible in wells with a high associated gas pressure in the annulus.

The second concomitant cause of the existing imperfections in the protection of the SEM is that the pressure sensor is not located at the reception of the electric centrifugal pump, but much lower - at the very bottom of the SEM. This leads to the fact that the pressure sensor will always show a slightly higher pressure than the pressure at the ESP intake, introducing uncertainty into the estimate of the pressure in the zone of entry of the well fluid into the electric centrifugal pump.

An object of the invention is to increase the protection efficiency of the installation of an electric centrifugal pump by eliminating the possibility of getting associated petroleum gas at the pump intake while reducing the dynamic level of the liquid (gas-liquid section) before being received in the ESP and below.

The technical task according to the invention is performed by the fact that in the method of protecting the installation of an electric centrifugal submersible pump, which consists in turning off the power to the submersible electric motor of the installation when a depth telemetry sensor is shown equal to or lower than a certain predetermined value, one pressure sensor is installed at the reception of the electric centrifugal pump (ESP), the second sensor pressure set in the annular space at the wellhead, the value of Ρ _min (sensor pressure, at which and below which the SEM is turned off) The well control station calculates in constant time mode as the sum of two pressures: the pressure of the liquid column above the P _hydro sensor and the gas pressure above the gas-liquid section (dynamic level) P _GLC :

$$P_{m\mathrm{and}n}=R_{g\mathrm{and}dR\mathrm{about}}+R_{RFR},\text{(2)}$$

moreover, the value of P _GLC is determined by calculation on the basis of their testimony of the second wellhead pressure transducer, and the pressure P _hydro is set to a constant value based on well conditions and characteristics of the downhole pump.

The pressure Р _{hydro is} determined on the basis of the passport data of the ESP, the physical properties of the liquid with the dissolved gas between the ESP and N _din (density and gas content), as well as the possibility of the situation when Р _ГЖР = 0 with the open gate of the MP well.

The pressure at the gas-liquid section in the annulus (MT) of the well depends on the pressure of the gas at the wellhead and the properties of associated petroleum gas, determined by the exponential Laplace-Babinet formula (p. 134 source: Korotaev Yu.P., Shirkovsky A.I. Dobycha , transport and underground gas storage.Textbook for universities.- M .: Nedra, 1984. - 487 p.) depending on R _mouth - pressure in the well MP at the wellhead. This pressure (P _mouth ) is measured by a sensor.

The method is implemented in an oil well equipped with an ESP and having in its underground equipment stationary pressure sensors installed at the wellhead and at the reception of a deep electric centrifugal pump. The arrangement of the sensors is shown in the drawing, where the numbers denote: 1 - casing string of the well, 2 - string of lift pipes, 3 - electric centrifugal pump of the installation, 4 - pressure sensor at the pump inlet, 5 - hydraulic protection of the ESP, 6 - submersible motor, 7 - PED power supply lines and feedback to the well control station 8, 9 — inlet openings to the ESP, 10 — pressure gauge in the annulus at the wellhead.

Using the above scheme, we compare the operation of two ESP protection systems: the one proposed and existing today in oil and gas companies in two situations: in the presence of high gas pressure in the well MP and in its absence.

Consider the general initial data for a vertical well:

- the depth of reception of the electric centrifugal pump N _ESP = 1000 m;

- the depth of the lower part of the submersible motor N _PED = 1016 m;

- the density of the gas-liquid composition (oil) between the SEM and the ESP ρ _w = 600 kg / m ³ ;

- the average temperature in the ESP zone is equal to T _cf = 293 ° K;

- the average value of the coefficient of gas compressibility z _cp = 1,0;

- engineering personnel set P _hydro = 0.60 MPa;

- the gas pressure in the annulus at the wellhead takes two values of P _mouth = 0.9 MPa (situation 1) and P _mouth = 0 MPa (situation 2).

The gas pressure in the annular space R _GZHR when reaching a dynamic level of reception in the ESP, that is, when N _dyn = N _ESP , is found by the Laplace-Babinet formula:

The proposed protection system is ESP. One pressure sensor 4 is located at the inlet to the ESP. Another pressure sensor 10 is located in the MP at the wellhead.

The first situation is in the well associated high-pressure gas and at the same time, the dynamic liquid level in the magnetic field approaches the reception of the ESP.

According to the invention, P _min = P _hydro + P _GLC = 0.6 + 1.0 = 1.6 MPa. If the pressure at the sensor located at the inlet of the ESP decreases, up to P _{min, the} submersible motor stops its operation. Find the height of the liquid column above the entrance to the ESP when the PED stops from the formula (2): P _hydro = P _min -P _GZHR = 1.6-1.0 = 0.6 MPa. This pressure corresponds to the following height of the liquid column above the entrance to the ESP: ΔН = Н _ESP- Н _din = Р _hydro / (ρ _w · g) = 0.6 MPa / (600 kg / m ³ · 9.8 m / s ² ) = 102 m. This height of the liquid excludes the ingress of free gas to receive ESP with subsequent negative impact.

The second situation is that the gas pressure in the magnetic field decreases to zero in the well, and at the same time, the dynamic liquid level in the magnetic field approaches the reception of the ESP. According to the invention, P _min = P _hydro + P _GLC = 0.6 + 0 = 0.6 MPa. Above the entrance to the ESP there is again a liquid column 102 m high. The deep installation is reliably protected from free gas.

The existing ESP protection system. There is only one pressure sensor, and it is located in the lower part of the submersible electric motor at a depth of N _PED = 1016 m.The submersible electric motor is switched off at P _min = P _hydro , that is, the component _{G of the GLC} in the equation (2) is absent. According to general conditions, the parameter P _hydro = 0.6 MPa.

The first situation is in the well associated high-pressure gas and at the same time, the dynamic liquid level in the magnetic field approaches the reception of the ESP. When the dynamic level decreases before receiving the ESP, the pressure sensor will record the gas pressure in MP: P _PED = P _GZHR = 1.0 MPa. This pressure is higher than P _min = P _hydro = 0.6 MPa, so the PED is not turned off by the protection and continues to work, and associated petroleum gas enters the ESP in a free state. This leads to overheating and vibration of the ESP and a quick failure.

The second situation - in the well, the gas pressure in the MP decreases to zero, and at the same time, the dynamic liquid level in the MP approaches the reception of the ESP. When the pressure sensor PEM equal to R _min : P _PED = P _min = P _hydro = 0.6 MPa, the control station disconnects the PED from the power supply. When the PED is turned off, the pressure at the inlet to the ESP will be less than this regulated value of P _min by the amount of hydrostatic pressure between the inlet of the ESP and the lower part of the PED (sensor installation location):

R _ESP = R _PED -ρ _w · g · (N _PED -H _ESP ) = 0.6 MPa - 600 kg / m ³ · 9.8 m / s ² · (1016-1000) m = 0.506 MPa.

The above calculations are presented in a more convenient tabular form:

Analysis of the table shows that in both situations that periodically occur in oil wells, the proposed method for protecting the ESP operation is better than the existing one. According to the invention, a technical result is achieved, namely, getting into the ESP intake of associated petroleum gas while reducing the dynamic level of the liquid (gas-liquid section) before being admitted to the pump and below. For the first time, it is proposed to take into account the pressure created by the gas component of the annulus of the well. It was also proposed to transfer the pressure sensor from the bottom of the SEM to the input to the ESP, and take into account the gas pressure at the wellhead using the second stationary sensor. All these innovations meet the criteria of “novelty” and “significant difference”.

The economic efficiency from the implementation of the invention is formed due to the longer and trouble-free operation of wells with ESP.

Claims (1)

A method of protecting the installation of an electric centrifugal submersible pump, which consists in turning off the power to the submersible electric motor (SEM) of the installation when a depth telemetry sensor is shown equal to or lower than a certain predetermined value, characterized in that one pressure sensor is installed at the reception of the electric centrifugal pump (ESP), a second pressure sensor is installed in annular space at the wellhead, value P _min - pressure sensor at which and below which turns off operation of the SEM, a borehole control station oh calculates a time constant as the sum of the two pressures: the liquid column above the pressure sensor P _hydro and gas pressure over a gas-liquid partition (dynamic level) P _GZHR:
P _min = P _hydro + P _GL
moreover, the value of P _GLC is determined by calculation based on their readings of the second wellhead pressure sensor, and the pressure P _hydro is set to a constant value based on the well conditions and characteristics of the downhole pump.