RU2773593C1 - Method for operation of a rod pumping unit - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: invention relates to the oil and gas industry and can be used in the operation of wells equipped with downhole rod pumps (DRP). To implement the method for operation of a rod pumping unit, a spring compensator is installed using a tap, a flange connection and a support on an exhaust line consisting of two sections with different values of the diameters of the conditional passage. The liquid enters the expanded section of the exhaust line, after which the flow loses part of its velocity, reducing pressure pulsation. With the steady dynamics of pressure pulsation change, the liquid alternately moves into the cavity of the spring compensator and is displaced due to the elastic forces of the springs at the time of the absence of pump supply, thereby equalizing the pressure. Then, with the help of a transition, the liquid passes from the expanded section to the narrowed section of the exhaust line to preserve throughput. The spring compensator is located at a minimum fixed distance from the wellhead equipment to ensure the least pressure pulsations. The selection of the values of the diameters of the exhaust line, the distance between the spring compensator and the wellhead equipment is calculated based on the dependence of the function of pressure drops at the outlet of the rod pumping unit on time, taking into account the technical and technological parameters of the pumping unit, as well as the rheological properties of the liquid affecting the amplitude of pressure pulsations.

EFFECT: decrease in the pressure pulsation of the rod installations and an increase in the reliability of the exhaust line and an increase in its total service life.

1 cl, 5 dwg

Description

The invention relates to the oil and gas industry and can be used in the operation of wells equipped with downhole rod pump units (USSHP) to increase the efficiency and reliability of operation, reduce the load on pumping equipment, increase the durability of the flow line.

Known downhole sucker-rod pumping unit, containing a pump, columns of pumping pipes and rods, a pneumatic compensator with a temperature controller, placed on the injection line at the wellhead at low temperatures to reduce pressure pulsation. The pneumatic compensator is equipped with an automatic operating pressure maintenance system, consisting of a heating element and a temperature sensor (RU 2724159, 06/22/2020).

The disadvantages of this technical solution are the inability to dampen the pressure pulsation in a wide range, increased energy and economic costs for maintaining a constant temperature, the complexity of the system during operation.

A known method of oil production using a sucker rod pump, including a change in the frequency of rotation of the crank of the pumping unit and consistent with it through the change in the angular velocity of the swing of the balancer, the change in the speed of the reciprocating movement of the wellhead rod. The frequency of rotation of the crank and the speed of the reciprocating movement of the rod matched with it is changed according to a sinusoidal law, smoothly accelerating the working stroke, at which the translational movement of the rod upwards reaches its maximum speed with the vertical position of the connecting rod and the crank at the bottom point, and proportionally slowing down the idling. This achieves a significant reduction in overloads on the sucker rods and the drive as a whole, which occur at the end of the idle stroke down and at the beginning of the stroke upwards when using traditional technologies (RU 2381383, 10.02.2010).

The disadvantage of this method is the uneven change in the velocity of the liquid, the deviation from its average value, which leads to pressure drops in the flow line and reduce its reliability.

Known downhole rod pumping unit containing a pump, columns of pumping pipes and rods, a vertical spring compensator installed on the injection line with a tap and a flange connection. The spring compensator is equipped with three vertically arranged compression springs for uniform distribution of the longitudinal load, the compression of which occurs at low, medium and high pressure fluctuation ranges, respectively (RU 2743115, 02/15/2021).

The disadvantage of this technical solution is the same type of flow line design with a constant diameter value, which does not allow to some extent to reduce the fluid flow rate and, consequently, the pressure drop.

The objective of the invention is to reduce the pressure pulsation of rod installations, increase the reliability of the flow line and increase its total working life, as well as reduce the cost of maintenance of wellhead equipment.

This problem is solved by the fact that in the method of operating a sucker-rod pumping unit, including the installation of a spring compensator on the flow line, according to the invention, the spring compensator is installed on the flow line, consisting of two sections, performed with different nominal diameters to reduce pressure pulsation, and placed on the minimum fixed distance from the wellhead valve, while the flowline contains a transition for a smooth change in the fluid flow rate, and the selection of values of larger and smaller diameters of the sections of the flowline and the distance from the compensator to the wellhead valve is carried out by calculation using the dependence function of the pressure drop at the outlet of the pumping unit from time to time, taking into account the required technical and technological parameters of the pumping unit and data on the pumped liquid and its rheological properties that affect the amplitude of the pressure pulsation.

In FIG. 1 schematically shows a general view of a downhole rod pumping unit and a flow line equipped with a spring compensator. In FIG. 2 shows the dynamics of pressure fluctuations at the outlet of a sucker-rod pumping unit for various values of the distance from the wellhead; in fig. 3 shows the dynamics of pressure fluctuations at the outlet of a sucker-rod pumping unit for various values of the diameter of the expanded part of the flow line; in fig. 4 and FIG. 5 shows the dependences of the amplitudes of pressure fluctuations on the value of the distance from the wellhead valve and the diameter of the flow line, respectively.

The design of the borehole rod pumping unit:

1 - machine - rocking chair;

2 - wellhead fittings;

3 - a column of pumping pipes;

4 - spring compensator;

5 - support;

6 - outlet from the flow line to the spring compensator;

7 - section of the flow line with a diameter exceeding the diameter of the main flow line;

8 - transition;

9 - section of the main flow line;

10 - overhead outlet;

11 - underground outlet.

The downhole rod pumping unit (Fig. 1) consists of a pumping unit 1, including wellhead fittings 2 and a tubing string 3. 5, installed under the outlet 6. To maintain the productivity and throughput of the pipeline system, the flow line is provided with a transition 8 to the narrowed section of the main flow line 9.

To ensure the convenience of maintenance of wellhead fittings during its operation, as well as the passage of various equipment, the flow line was laid both by above-ground and underground methods using above-ground and underground outlets 10, 11, respectively.

The method is implemented as follows.

Downhole rod pumping unit 1 supplies fluid to the flow line, consisting of two sections, with a spring compensator 4 installed on it using a branch 6 and a flange connection. The liquid enters the expanded section 7 of the flow line with a diameter greater than the diameter of the main flow line 9, losing part of its velocity due to the occurrence of local expansion, thereby slightly reducing the value of the pressure pulsation. In view of the occurrence of pulsations, a certain volume of liquid alternately enters the cavity of the spring compensator 4 and is displaced by the work of the elastic forces of the springs at the moment of the absence of pump supply, thereby bringing the amplitude of pressure fluctuations closer to its average value. The movement, speed and acceleration of the compensator piston 4 is determined using the equation of motion of the compensator, taking into account losses from the friction of the piston against the walls of the housing, the compressibility of the gas in its upper section, as well as the influence of parameters (diameter and mass of the piston, spring stiffness) on the dynamics of its work:

where m _a.c. - weight of the compensator piston, kg;

- ускорение поршня компенсатора, м/с²;

- acceleration of the compensator piston, m/s ² ;

x _p.k - displacement of the compensator piston, m;

A _p.k - cross-sectional area of the compensator piston, m ² ;

p _expiration - pressure at the outlet of the pump valve, Pa;

p _g - gas pressure in the upper section of the compensator, Pa;

c _p - total stiffness of springs, N/m;

d _k.sht - diameter of the compensator rod seal, m;

D _c.p - diameter of the compensator piston seal, m;

b _c/pc - compensator rod seal width, m;

b _k.p - width of the compensator piston seal, m;

k is the coefficient of friction.

After the liquid is displaced by the piston from the cavity of the compensator at the moment of the suction stroke of the pump, its further movement is carried out using transition 8, for a gradual increase in speed without sharp drops, followed by outflow into the narrowed main part of the flow line 9.

The spring compensator 4 is located at a fixed distance L from the wellhead valve 2, and is also equipped with a support 5 to reduce static weight loads on the flow line and increase the durability of its connecting elements. The selection of the optimal location of the spring compensator relative to the wellhead is necessary, since the increase in pressure amplitude occurs with an increase in the specified distance L. To ensure the passage of specialized units during the construction and repair of newly constructed and existing flow lines, as well as maintenance of the wellhead ways of laying a flow line using above-ground and underground outlets 10, 11, respectively.

The selection of values of larger and smaller diameters of the flow line, as well as a fixed distance L from the wellhead valve 2 to the spring compensator 4 is based on the dependence of the function of pressure drops on time during the operation of the sucker rod pumping unit, taking into account the balances of fluid flow rates, as well as the required performance. Pressure drops are determined by the following function, depending on the factors affecting the pulsation: compressibility, viscosity, liquid density, parameters of the spring compensator, as well as the design of the pump plunger, rod strings and tubing:

where E _W is the compressibility of the liquid, MPa ^-1 ;

V _W - the volume of the incoming liquid, m ³ ;

α is the coefficient of fluid flow through the valve;

p - density of injected fluid, kg/m ³ ;

μ - dynamic viscosity, Pa⋅s;

- угловая скорость рад/с;

- angular velocity rad/s;

r - crank radius, m;

t - time, s;

μ - dynamic viscosity, Pa⋅s;

- площадь кольцевого сечения между внутренним диаметром цилиндра насоса и наружным диаметром штанг, м²;

- area of the annular section between the inner diameter of the pump cylinder and the outer diameter of the rods, m ² ;

A _p.k - cross-sectional area of the compensator piston, m ² ;

ƒ _cl - cross-sectional area of the discharge valve, m ² ;

x _p.k - displacement of the compensator piston, m;

d _c - inner diameter of the pump cylinder, m;

d _pcs - outer diameter of the pump rod string, m;

D _tubing - inner diameter of the tubing string, m;

D _{outflow.expand} - inner diameter of the expanded outflow pipeline, m;

D _{constricted flowpipe} ^_ internal diameter of the constricted flowline, m;

D _ngs - internal diameter of the oil and gas gathering pipeline, m;

L - distance from the wellhead fittings to the spring compensator, m;

L _discharge - the length of the discharge line (distance from the spring compensator to the point of connection to the measuring installation), m;

L _ngs is the length of the oil and gas gathering pipeline (distance from the point of connection of the flow line to the measuring installation to the stop valve assembly), m;

L _tubing - tubing string length, m;

p _class.in - pressure at the inlet to the valve, corresponding to the pressure in the cavity of the pump, Pa;

p _cl.out - pressure at the outlet of the pump valve, Pa;

p _ks.in - inlet pressure in the annular section between the rod string and the tubing, corresponding to the pressure at the outlet of the valve, Pa;

p _ks.out - pressure at the outlet of the annular section between the rod string and the tubing, Pa;

p _{outflow expand.in} - pressure at the inlet of the expanded flow line, corresponding to the pressure at the outlet of the annular section between the rod string and tubing, Pa;

p _{vykd.expansion.out} - pressure at the outlet of the expanded flow line, Pa;

p _{vykid.narrow.in} - pressure at the inlet of the narrowed flow line, corresponding to the pressure at the outlet of the expanded part of the flow line, Pa;

p _{vykid.suzh.vyh} - pressure at the outlet of the narrowed flow line, Pa;

p _ngs.in - pressure at the inlet of the oil and gas gathering pipeline, corresponding to the pressure at the outlet of the AGZU, Pa;

p _ngs.out - pressure at the outlet of the oil and gas gathering pipeline, corresponding to the pressure at the reception of the metering station, Pa.

An example of the implementation of the method.

Mathematical modeling of the process of changing the pressure dynamics at the outlet of a sucker-rod pumping unit during its operation, equipped with a spring compensator installed on the expanded part of the flow line, is carried out. Well design: tubing diameter 48 mm, depth 1000 m. Technological operation mode: stroke length of the balancer head 2 m, number of strokes per minute 12, plunger diameter 38 mm, average diameter of sucker rods 22 mm. The pressure at the pump intake is 9 MPa. Liquid properties: density of pumped liquid 900 kg/m ³ , coefficient of its compressibility 550 MPa ^-1 , value of dynamic viscosity varied within (5…155)-10 ^-3 Pa⋅s.

In FIG. 2 shows the dynamics of pressure fluctuations at the outlet of the sucker-rod pumping unit at various values of the distance from the wellhead fittings and dynamic viscosity equal to 80 mPa⋅s; 13 is a graph of the pressure function at a distance value L=3 m; 14 is a graph of the pressure function at a distance value of L=5.5 m. It can be seen from the presented dependencies that with increasing distance, the pressure increase also increases by 0.003-0.005 MPa.

In FIG. 3 shows the dynamics of pressure fluctuations at the outlet of a sucker-rod pumping unit for various values of the diameter of the expanded part of the flow line and a dynamic viscosity of 80 _mPa⋅s ; 16 - graph of the function of pressure at the value of the diameter D _discharge = 89 mm; 17 is a graph of the pressure function at a diameter value D _ejection = 57 mm. It can be seen from the presented dependences that an increase in the diameter leads to a decrease in the amplitude of pressure fluctuations. With a flow line diameter of 114 mm, the pressure pulsation was about 3.06 MPa, and with a smaller diameter value of 57 mm, the pulsation was more than 3.13 MPa.

In FIG. 4 and FIG. 5 shows the dependences of the amplitudes of pressure fluctuations on the value of the distance from the wellhead valve and the diameter of the flow line, respectively. When selecting the parameters of the flow line and the minimum distance from the wellhead fittings, it is necessary to operate with the value of the viscosity of the pumped liquid. The calculation was made for different ranges of dynamic viscosity - small, medium and high: 18, 21 - graphs of the amplitude function at the value of viscosity μ=5⋅10· ^-3 Pa⋅s; 19, 22 - graphs of the amplitude function at a viscosity value μ=80⋅10 ^-3 Pa⋅s; 20, 23 - graphs of the amplitude function at a viscosity value μ=155⋅10 ^-3 Pa⋅s.

The selection of parameters was carried out as follows: a certain calculated step was chosen for the values of the diameter and distance, curves were constructed that characterize the dependence of the amplitude of pressure fluctuations on the diameter or distance, respectively. On the basis of the obtained curves, along the parameter axes (diameter or distance), perpendicular lines are plotted until they intersect with the graph of the function with the accepted calculated step. Parallel lines are plotted (relative to the parameter axes) with the accepted calculated step up to the intersection with the pressure amplitude axis. On the basis of the data obtained, an analysis of the parameters providing the minimum value of the pressure amplitude is carried out.

In this case, the spring compensator should be located at a distance of 0.5-2 m on the extended section of the flow line with an outer diameter of 114 or 159 mm with a transition to a narrowed section of the main flow line with a diameter of 89 mm, selected on the basis of the required performance.

The proposed method for operating a sucker-rod pumping unit makes it possible to reduce the pressure pulsation at its outlet without changing the design of the unit itself, which implies wide application not only for designed and newly constructed plants, but also for existing ones. At the same time, the implementation of this method on an industrial scale does not require significant costs, which is beneficial from the point of view of economic efficiency. Reducing the pressure pulsation at the outlet of the installation will reduce the cyclic loads on the pipeline system, which will increase its residual life. The pumping unit is also less susceptible to the influence of cyclic loading from the side of the injected fluid flow, which generally increases its reliability during operation.

Claims (1)

A method for operating a sucker-rod pumping unit, including the installation of a spring compensator on the flow line, characterized in that the spring compensator is installed on the flow line, consisting of two sections made with different nominal diameters to reduce pressure pulsation, and located at a minimum fixed distance from the wellhead valves, while the flow line contains a transition for a smooth change in the fluid flow rate, and the selection of values of larger and smaller diameters of the sections of the flow line and the distance from the compensator to the wellhead valve is carried out by calculation using the function of the dependence of the pressure drop at the outlet of the pumping unit on time, taking into account the required technical and technological parameters of the pumping unit and data on the pumped liquid and its rheological properties that affect the amplitude of the pressure pulsation.

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