EP0420751A1 - Procedure for pumping a gas/liquid mixture from an oil recovery well and device for carrying out such method - Google Patents

Abstract

The present invention relates to a method of pumping a two-phase mixture of gas liquid in an extraction well (11) whose initial gas percentage is greater than approximately 40% by volume, characterized in that it consists:
- to lower the percentage of free gas below 40% by using at least one first centrifugal separator module (3,4);
- cooling the drive motor by an annular flow of the mixture from the first separator module (3,4) around the motor (9), a mixture whose proportion of gas has been brought below 40% to increase its heat capacity and its speed of passage around the engine;
- lowering the percentage of gas by volume to around 10% by using at least one second centrifugal separator module (14);
- pumping the fluid thus obtained by a centrifugal pump (16) driven by the motor (9).

Description

The present invention relates to a method of pumping a liquid gas mixture in an oil extraction well and the device for implementing the method.

The production of hydrocarbons in an oil well is done, either as part of a naturally eruptive well, naturally, or artificially, and in this case the well must be activated. In the first case, the bottom pressure is sufficient to allow the fluid to rise to the surface. In the second case, the pressure is insufficient to allow extraction and this requires an assistance mode to ensure the ascent of the fluid to the surface. The well is then activated.

In addition, the eruptive wells, after a certain period of operation, are no longer eruptive and they must also be activated.

Consequently, to carry out the exploitation of fluids constituted by hydrocarbons, different activation techniques are used, such as:
- gas lift (gas injection at the bottom);
- alternative pumping;
- centrifugal pumping;
- jet effect pumping etc.

Each of these different activation means will be used according to the characteristics of the well and the range of application of the means. So we will use the gas lift when the fluid is already gassed or vice versa we will not use pumping if the quantities of gas are large.

One of the classic and widely used means of electric centrifugal pumping. The classic assembly consists of a centrifugal pump multicellular, an electric motor and a protector located between the motor and the pump and whose role is to seal around the motor shaft so that external fluids do not enter the motor .

However, this type of equipment has limitations due in particular to the proportion of gas contained in the mixture to be extracted from the well. Thus, when the proportion in the mixture produced reaches values of 10% by volume relative to the total effluent, the centrifugal pump can no longer operate. The percentages mentioned in the text are the percentages by volume at the background conditions of pressure and temperature. This drawback considerably limits the uses of centrifugal pumping according to the characteristics of the well and to cope with this problem, a centrifugal separator has been designed and used which, placed upstream of the pump between the latter and the motor, makes it possible to carry out partial separation of the gas.

Such a system allows, when the flow rates are relatively low, less than 300 to 400 m3 per day, to obtain a partial elimination of the gas which will allow the normal operation of the pump. This is possible provided that the percentage of free gas in the initial mixture is less than about 40% by volume. In this case, the separator reduces the percentage of free gas to around 10%.

In the case of mixtures greater than about 40%, in addition to the fact that the above device is no longer operational, the heat capacity of the mixtures is insufficient and the cooling of the electric motor can no longer be satisfactorily ensured.

A first aim of the invention is therefore to propose a method of pumping a two-phase liquid gas mixture allowing the exploitation of wells with a percentage of free gas in the initial mixture greater than about 40% by volume.

This object is achieved by the fact that the process for pumping a two-phase liquid gas mixture into an extraction well, the initial gas percentage of which is greater than approximately 40% by volume, is characterized in that it consists:
- to lower the percentage of free gas below 40% by using at least one first centrifugal separator module;
- cooling the drive motor by an annular flow of the mixture from the first separator module around the motor, a mixture whose proportion of gas has been reduced to increase its heat capacity and its speed of passage around the motor;
- to lower the percentage of gas by volume to around 10% by using at least one second centrifugal separator module;
- to pump the fluid thus obtained by a centrifugal pump driven by the motor.

A second object of the invention is to propose a device allowing the implementation of the method and capable of solving both the problem of pumping mixtures whose gas quantities can range up to 99% by volume and the problem of cooling of the drive motor of the device.

This object is achieved by the fact that the device comprises:
- A first module, gas separator in a mixture, centrifugal, with axial flow, arranged in a cylindrical envelope and whose separated gases are evacuated outside the envelope;
a cooling module comprising an external envelope in leaktight connection with the envelope of the first separator module and comprising inside a second coaxial cylindrical envelope containing a electric motor surrounded on both sides in the longitudinal direction of protectors ensuring sealing upstream and downstream at the motor drive axes;
means at the inlet of the cooling module, to divert the axial flow of the first separator module outside the second envelope and
means at the outlet of the cooling module for bringing the flow in the axis of a centrifugal pump module connected to a train of fluid evacuation tube at the outlet of the cooling module, said centrifugal pump module and the separator module being driven by the motor shaft.

Another object is to adapt the system according to the characteristics of the well by the use, either of a modular system, or of a fixed system with variable drive control.

This object is achieved by the fact that the device comprises at least a second centrifugal separator module between the cooling module and the centrifugal pump module.

According to another characteristic, this object is achieved by the fact that the first module comprises at least two centrifugal separators mounted in series so that the axial output flow of one constitutes the input flow of the second and of the coupling means in rotation of the first and second separator.

According to another characteristic, the coupling means consist of an electromagnetic clutch.

According to another characteristic, the device comprises at each end a centering device relative to the extraction well.

• - les figures 1A et 1B représentent la constitution du dispositif permettant la mise en oeuvre du procédé de l'invention ;
• - la figure 2 représente une vue d'un dispositif de centrage utilisé dans l'invention.

Other characteristics and advantages of the present invention will appear more clearly on reading of the description below made with reference to the appended drawings in which:

• - Figures 1A and 1B show the constitution of the device for implementing the method of the invention;
• - Figure 2 shows a view of a centering device used in the invention.

FIG. 1A represents the upstream part of the pumping device allowing the implementation of the method according to the invention. This device comprises a centralizing element (1) which may or may not be sealed, the central tube (100) of which directs the mixture of gas and fluid to a first centrifugal separator (3) whose outlet (30) for discharging the gases discharges the gases in the annular space between the external cylindrical envelope (32) of the separator and the tube (11) constituting the wall of the extraction well. The fluid gas mixture, the percentage of which has been lowered by the first separator, is discharged through an axial orifice (31) in the direction of a second separator (4) with a view to a further reduction in the percentage.

This separator (4) evacuates the gas through an orifice (40) in the annular space and the gas fluid mixture through an axial orifice (41) in the direction of a cooling module (10) constituted by a deviating element (6) the axial flow of the separator (4) through lateral orifices (60) towards an annular space formed between an external tube (10 A) and the successive external tubes (80,90,120) respectively of the protective modules (8), motor (9) and protector (12) mounted inside and coaxially with the tube (10 A) thus forming the cooling module (10).

The protective modules (8, 12) make it possible to ensure sealing at the level of the motor output shafts (9) upstream and downstream. In this way the motor element (9) is protected from contact with the fluids circulating in the device. On the other hand, the fluid flowing in the annular space formed between the tube (10) and the external envelopes (80,90,120) respectively forming the first protector, the motor and the second protector ensure cooling all the more efficient of the engine, that the percentage of gas in the mixture has been brought to the lowest possible level below 40%. At the downstream end of the cooling module, a diverter module (13) allows, thanks to the orifices (130) to bring the flow axially in the separating element (14) which follows the cooling module.

This separator (14) analogous to the other separators evacuates the gas through the orifice (140) towards the annular space between the outside of the envelope (142) of the separator device and the tubes (11) constituting the wall from the extraction well. This separator (14) evacuates the axial flow of the mixture to a centrifugal pump (16) through the axial orifice (141). The outlet of the centrifugal pump (16) is connected to a set of tubes (18) which makes it possible to raise the liquid practically separated from its gas to the surface.

At the output of the device, it is also possible to use a centering device (17).

The motor (9) drives by drive shafts which extend inside the device, both towards the separators located upstream and downstream and towards the centrifugal pump.

In operation, the two-phase mixture (2) enters the system and part of the gas is separated and discharged through the annular space at the level of the first centrifugal separator (3) with axial flow.

The remaining mixture enters the second separator (4) where the same operation is carried out. For a flow rate of the order of 200 m3 per day, with a separator having a diameter of 125 mm driven at 3000 revolutions / minute, the percentage of free gas at suction (2) being 99%, the percentage at the outlet of the first separator (3) can be reduced to around 60%. second separator will bring the percentage of gas to around 30%.

The fluid is thus sufficiently degassed to have sufficient heat capacity to ensure effective cooling of the engine. The fluid leaving the second separator (4) passes into the engine cooling module and then enters the third separator (14) to complete its journey in the centrifugal pump and then be evacuated to the surface inside the train tube (18). The gas on its side joins the surface through the annular space formed between the tube train (18) and the tubes (11) constituting the wall of the extraction well. The third separator will bring the percentage of gas from 30% at the inlet to a percentage compatible with the proper functioning of the pump (16) generally less than 8%.

It is obvious that the third separator (14) is optional and depends on the percentage of gas contained in the initial two-phase liquid. Thus, in the case of an initial two-phase mixture whose percentage of gas is slightly greater than 70%, the two separators (3,4) will be used, but the last separator (14) may possibly be dispensed with. On the other hand, in the case of a two-phase mixture of between 70 and 40%, only one separator (3) will be used upstream of the motor and a second separator (14) downstream of the motor.

In the variant shown, the drive shafts of the first and second separators (3,4) are mechanically connected in rotation by a sleeve (33).

In an alternative embodiment of the invention, these shafts can be mechanically connected by an electromagnetic clutch controlled from the surface to implement, as required, one or two separator modules upstream of the engine.

FIG. 2 shows a sealed centering element (1) used upstream of the device. This centering element consists of anchoring corners (101) connected, on the one hand to the external tube (11) of the extraction well by seals (103), and on the other hand to the internal tube ( 100) for suction of the two-phase liquid (2) by seals (102), so as to channel the two-phase mixture towards the inside of the tube (100).

The leaktight centering device (17) located downstream of the pumping device will only comprise spacers for holding the tubes (18) to allow the flow of gas outside the tube (18).

It is obvious that, depending on the case, a non-watertight centralizer (1) can be used. Similarly for the output centering device (17), it is possible, if necessary, to use a waterproof centering device.

Claims (6)

1. Method for pumping a two-phase liquid gas mixture into an extraction well (11) whose initial gas percentage is greater than approximately 40% by volume, characterized in that it consists
- to lower the percentage of free gas below 40% by using at least one first centrifugal separator module (3,4);
- cooling the drive motor by an annular flow of the mixture from the first separator module (3,4) around the motor (9), a mixture whose proportion of gas has been brought below 40% to increase its heat capacity and its speed of passage around the engine;
- lowering the percentage of gas by volume to around 10% by using at least one second centrifugal separator module (14);
- pumping the fluid thus obtained by a centrifugal pump (16) driven by the motor (9). 2. Device for implementing the method according to claim (1) characterized in that it comprises:
- a first module, separator (3) of gas in a mixture, centrifugal, with axial flow disposed in a cylindrical envelope (32) whose separated gases are evacuated outside the envelope and a cooling module (6, 10,13) comprising an outer casing (10) in leaktight connection with the casing of the first separator module and comprising inside a second coaxial cylindrical casing (80,90,120) containing an electric motor (9) surrounded on the side and d 'other in the longitudinal direction of protectors (8,12) sealing upstream and downstream at the motor drive axes;
- Means (6) for deflecting the axial flow outside the second envelope (80,90,120) at the inlet of the cooling module (10); and
- Means (13) at the outlet of the cooling module (10) for reducing the flow in the axis of a centrifugal pumping module (16) connected to a train of fluid discharge tube (18), said modules pump and separator (3) being driven by the motor shaft (9). 3. Device according to claim 2, characterized in that it comprises at least a second centrifugal separator module (14) between the cooling module (10) and the centrifugal pump module (16). 4. Device according to claims 2 or 3, characterized in that the first module comprises at least two centrifugal separators (3,4) mounted in series so that the axial output flow of one constitutes the input flow of second and means (33) for rotationally coupling the drive shafts of one and the other. 5. Device according to claim 4, characterized in that the coupling means consist of an electromagnetic clutch controlled from the surface. 6. Device according to one of the preceding claims, characterized in that it comprises at each end a centering device (1,17) relative to the extraction well (11).

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