EP0435716A1 - Device for separation of a gas-liquid-mixture as supply for a downhole pump - Google Patents

Abstract

The present invention concerns a device for separating a mixture of free gas and liquid at the inlet of a pump (3) connected to a low end of a tubular column (2) at the bottom of a borehole. The pump (3) is connected to the tubular column (2) by an intermediate production pipe (6) and is inserted in a fluid inlet device (7, 8) of which one low end is covered and one high end comprises orifices (9) for the inlet of fluid, the said pump being placed inside the said inlet device, in the proximity of its low end, the said inlet device comprising, in the vicinity of its low end, a device forming at least one valve (21, 22). Application to pumping in greatly inclined boreholes. <IMAGE>

Description

The present invention relates to a device for separating a mixture of gas and liquid, this mixture possibly in particular consisting of hydrocarbons, at the intake of a pump connected to a lower end of a tubular column at the bottom of a drilled well.

The hydrocarbon production installations use, after the installation of wells drilled towards the reservoir of the geological formation, pumping systems intended to bring the oil up to the surface. For this operation, a tubular column serving as a conduit for producing the hydrocarbons is lowered into the drilled well, at the end of which is a pump.

The pumps used can be of different types: piston pumps, centrifugal pumps, hydraulic pumps, balance pumps, rotary positive displacement pumps (commercially called "MOINEAU Pump").

If such pumps operate satisfactorily when the pumped fluid is mainly composed of liquid, problems arise and develop when a volume of free gas is mixed with the production fluid. In fact, if the inlet pressure of a fluid to a pump is lower than the bubble pressure above which all the gas is dissolved in the oil, the pumps admit free gas mixed with the production fluid.

Under these conditions, this results in a low pumping efficiency if the measured flow rate of the reservoir is compared to the theoretical flow rate of the pump and an acceleration of the operation of the pump which has repercussions on the increase in the rotation speed for the pumps with piston.

The prior art illustrated by patents GB-983,644 and US-2,969,742 has solved this problem by using a gas / liquid separation device mounted around the pump to minimize the presence of suspended gases in the liquid during the pump operation. The pump is introduced at the bottom of a tubular conduit plugged at its lower part and provided with inlet orifices at its upper part so that, at the level of the separator orifices, the free gas tends to evacuate towards the surface, while the oil is sucked up by the pump.

However, such an assembly has a serious drawback which corresponds to the dry running of the pump when the liquid level does not reach the intake orifices.

The most harmful effect is found in a reduction in the service life of positive displacement pumps of the "MOINEAU" type in which the gas introduced tends to filter in the elastomer of the stator and therefore to deform the helical internal gears of the pump. . In other types of pumps, wear increases with the risk of blocking the pump.

The present invention therefore aims to overcome the aforementioned drawbacks of dry operation, wear and deterioration of the pumps.

The present invention relates to a device for separating a mixture of free gas and liquid at the intake of a pump connected to a lower end of a tubular column at the bottom of a drilled well, the pump being connected to the tubular column by an intermediate production tube and being introduced into a fluid admission device of which a lower end is closed and an upper end has orifices for introducing fluid, said pump being placed inside said device admission, near its lower end.

According to the invention, the intake device comprises in the vicinity of its lower end a device forming at least one valve.

The intake device may comprise a tube and the device forming at least one valve may be placed in the axis of said tube.

The intake device may include a cylindrical tube, the device forming at least one valve, may be placed on the cylindrical walls of said intake device.

The intake device may comprise an intake duct coaxially surrounding the intermediate production tube and the pump, the intake duct being extended by a separation duct provided circumferentially with orifices and held around said tubular column by a piece of fixation.

The intermediate production tube and the pump can be kept coaxial with the intake duct by centralizers.

The device forming at least one valve may include a shutter, such as a ball or a valve, constantly stressed by elastic means blocking an opening for introducing fluid into the intake duct.

The elastic means may have a compression resistance at a minimum pressure, said minimum pressure corresponding to a level of liquid in the intake duct above the pump.

The intake duct and the separation duct can be held in the well drilled by stabilizers.

The length of the fluid intake device can be chosen so as to develop a pressure difference of a few bars between the intake level of the pump and the level of the orifices for introducing the fluid into said device.

The present invention applies to a pumping installation in a drilled well comprising a separation device, has a low zone whose orientation varies from vertical to a steep inclination.

• la figure 1 représente une coupe d'un puits foré à zone basse fortement inclinée.
• les figures 2 et 3 représentent des dispositifs de séparation gaz/liquide associé à une pompe à l'extrémité d'une colonne tubulaire comportant respectivement deux variantes différentes de dispositif d'obturation.

A particular embodiment of the invention will now be described in more detail which will make it better understand the essential characteristics and the advantages, it being understood however that this embodiment is chosen by way of example and that it is not at all limiting. Its description is illustrated by the appended drawings in which:

• FIG. 1 represents a section of a drilled well with a strongly inclined low zone.
• Figures 2 and 3 show gas / liquid separation devices associated with a pump at the end of a tubular column respectively comprising two different variants of the closure device.

FIG. 1 represents a drilled well 1 into which is introduced a pump 3 placed in an active position at the bottom of the well by a tubular conduit or column 2. The drilled well comprises near its surface a practically vertical zone extended downwards by a part deflected to become, at the bottom, strongly inclined in an area with a high content of withdrawable fluid. The present invention applies very particularly in the case of highly deviated wells, but it also retains all of its advantages in the case of vertical wells.

The pump 3 fixed at the end of the column 2 is introduced from the surface and progresses into the well by the addition of tubular sections.

Then introduced internally to the conduit a set of drive rods 30 placed end to end whose rotation is controlled by a drive head 23 connected to a motor 24 which may be of a type commonly used in pumping installations. The rotation of the rods 30 initiates the pumping device 3 which brings up the fluid circulating at the bottom of the well by the tubular column 2 to be evacuated towards the storage conduits 27. Valves 25 regulate the distribution of the pumped fluid on the surface.

Pump 3 is introduced at the end of the column tubular 2 in a separation device 17 aimed at bringing the free gas suspended in the liquid to the surface, while the latter is sucked towards the bottom of the separation device at the inlet of the pump 3.

The reference 31 designates a shutter type valve.

The constitution of this separation device is clearly visible with reference to FIG. 2.

The lower end of the tubular column 2 at the bottom of the well is attached around its circumference to one end of an intermediate production tube 6. The other end of this intermediate tube is connected to the outlet of the pumping device. In the example shown, a "MOINEAU" type pump is used, but it is understood that the advantages of the present invention would apply equally favorably in the case of a piston pump, a centrifugal pump, or a pendulum pump.

The "MOINEAU" pump 3 comprises a stator 4 provided with a tubular protective steel casing, covering an elastomer part or active part of the stator internally producing a helical gear.

A set of rods 30 placed end to end is disposed inside the tubular column 2, passes through the intermediate production tube 6, and supports a rotor 5 so as to transmit to it a rotary movement controlled at the surface. This rotor 5 has on its surface a helical gear associated with the stator 4.

The pump / intermediate production tube assembly is introduced into an intake duct 7, produced in the form of a tubular pipe open at its two ends. A first end is extended by a separation conduit 8 consisting of a tubular strainer provided with orifices 9 for introducing the fluid inside the conduit 7.

The separation duct 8 and the intake duct 7 are connected to each other by a circular ring 15.

The separation duct 8 is kept fixed around the intermediate production tube by a connecting member 16, this member comprising a threaded interior zone into which the upper end of the separation conduit 8 is screwed.

This member 16 also ensures the coaxial maintenance and the end-to-end positioning of the tubular column 2 and of the intermediate production tube 6.

In order to keep the pump 3 and the intermediate tube 6 coaxial with the intake duct in its axis, centering devices 10 are placed around these elements. These centering devices are, for example of the blade type, well known in drilling techniques soils. Other types of centralizers can also be used, for example rubber centralizers. These centralizers also have the advantage of limiting the oscillation movement of the pump along a section of the well.

Stabilizers 11 of the aforementioned type are also placed around the intake duct 7 to place the assembly in the axis of the well.

According to the invention, the lower end of the intake duct is provided with a closure device 31 comprising a part 20 providing a closure in which a valve is formed. This valve consists of a ball 21 constantly urged to block an opening for introducing fluid 23 by elastic means, such as, for example, a helical spring 22.

The example described in Figures 1 and 2 discloses the use of a valve placed at the end of the intake duct substantially in the axis of the pump. According to this embodiment, there is a risk of accumulation of sediment above the orifice 42 which can clog the latter and hamper the functioning of the closure device 31.

The embodiment of Figure 3 avoids this risk. The device according to this embodiment comprises one or more valves arranged circumferentially on the lateral or cylindrical walls of the lower end of the intake duct, the requisite being to be below the intake level of the pump.

The shutter system 32 shown in FIG. 3 comprises two shutter devices 33 and 34 positioned under the pump 3 and oriented in diametrically opposite directions. The closure devices 33 and 34 are superimposed relative to the axis of the intake duct 7.

By using two obturation devices, the operational safety of the obturation device is reinforced, since it suffices that one of the two obturation devices operates to ensure a continuous supply of fluid to the pump.

These two shutter devices being identical, only one will be described.

The shutter device 33 comprises a shutter 35 having a conical bearing surface 36 which cooperates with a conical seat 37 secured to the intake duct at its lower end.

The shutter 35 is guided by a cylindrical rod 38 which cooperates with a cylindrical housing 39 also carried by the intake duct 7.

Return means 40, such as a helical spring surrounding the rod 38, applies the shutter 35 to its seat 37.

The orientation of the conical surfaces of the shutter 35 and of the seat 37 is such that the shutter device prevents the flow of a fluid coming from inside the intake duct 7 and going towards the annular space 41 defined by the walls of the well and the external surface of the intake duct 7.

The principle of separation of the free gas from the liquid is carried out as follows, with reference to FIG. 2.

The gas / liquid mixture rises in the well and meets the closure device which keeps the ball in blocking of the opening 23. The mixture progresses laterally around the intake duct 7 to the separation duct 8. The assembly pumping device has been lowered into the well, so that the dynamic level of the mixture (represented by line A in FIG. 1) is substantially above the separation pipe.

The orifices regularly arranged around the duct of separation 8 allow the introduction of the fluid into the intake duct. When the fluid is entrained at the bottom of the intake duct, a degassing phenomenon occurs at the level of the mixing surface; the gas escaping to the surface through the well and the fluid falling back into the intake duct.

However, problems develop if the dynamic level drops below a limit position (represented at A in FIG. 2) or the intake orifices 9 of the separation duct. Indeed, if the level is lower (such as the level represented by line B), there will no longer be any introduction of fluid into the intake duct which will gradually empty, up to a stage where the pump will no longer suck in fluid and therefore run dry.

In the case of a descent of the dynamic level above the orifices 9, the level stabilizes in the well while the pumping action rapidly lowers the level inside the conduit creating a difference in level d. This difference in level generates a pressure difference which compensates for the effect of the spring against the shutter ball 23.

This pressure difference implies a force against the ball which moves away from its seat and allows the entry of the fluid / gas mixture directly through the lower end of the assembly. The pump is therefore constantly supplied with fluid. It then remains only to operate on the operating conduits, or reduce the speed of rotation and therefore the flow rate of the pump to promote an increase in the dynamic level at the height of the separation conduit 8. The pressures balance then between the outside and the inside of the intake duct 7, the ball comes to rest on its seat to block the opening and the separation phenomenon can again take place.

This pressure balancing process is also carried out when the assembly is initially lowered and the intake duct 7 is empty of any fluid. In this state the pump is not yet running and when pressure balancing is completed, the pump is commissioned.

The choice of the helical spring will therefore be made so that the valve is opened when the fluid level in the intake duct 7 is midway between the pump and the separation duct (represented by the line C).

In the case where the device is equipped with the variant of the closure device shown in FIG. 3, the principle of separation of the free gas from the liquid is identical to the principle described above for FIG. 2 with the variant close to the operation of the shutter device, the main steps of which are given below.

In the case of a descent of the dynamic level below the orifices 9, the level stabilizes in the well while the pumping action rapidly lowers the level inside the conduit creating a difference in level d. This difference in level generates a pressure difference which compensates for the effect of the return means 40 against the shutter 35.

This pressure difference implies a force against the shutter 35, which moves away from its seat 37 and allows the entry of the fluid / gas mixture directly through the lower end of the assembly. The pump is therefore constantly supplied with fluid.

It is sufficient that only one of the closure devices works, the devices being able to operate alone or simultaneously.

It then remains only to operate on the operating conduits, or reduce the speed of rotation and therefore the flow rate of the pump to promote an increase in the dynamic level at the height of the separation conduit 8. The pressures balance then between the outside and the inside of the intake duct 7, the shutter 5 comes to rest on its seat 37 to block the opening and the separation phenomenon can again take place.

All that has been said previously for the closure device described in Figure 2 with regard to the process balancing and the choice of the helical spring remains valid for the device described in Figure 3.

In a preferred embodiment in the case of a well orientation at 70 °, as shown in FIG. 1, the intake duct 7 has a length L of practically 60 meters and the intermediate production tube 6 has a length of 45 approximately meters, the pump and a fluid reservoir then having a length L of 15 meters.

The separation conduit 8 has a length of 1 meter.

However, the length of the intake duct 7 can be adapted in the case of a different well orientation, so as to constantly achieve a pressure difference of a few bars between the intake level of the pump 3 and the level of the orifices. 9 of the separation duct.

The present invention applies very particularly in the case of highly deviated wells which can approach substantially the horizontal. However, it finds the same applications in the case of vertical wells.

Naturally, the invention is in no way limited by the features which have been specified in the foregoing or by the details of the particular embodiment chosen to illustrate the invention. All kinds of variants can be made to the particular embodiment which has been described by way of example and to its constituent elements without departing from the scope of the invention. The latter thus includes all the means constituting technical equivalents of the means described, as well as their combinations.

Claims (10)

Device for separating a mixture of free gas and liquid at the intake of a pump (3) connected to a lower end of a tubular column (2) at the bottom of a drilled well, the pump (3) being connected to the tubular column (2) by an intermediate production tube (6) and being introduced into a fluid intake device (7, 8), a lower end of which is closed off and a high end comprises openings (9) for introducing fluid, said pump being placed inside said intake device, near its lower end, characterized in that said intake device comprises, in the vicinity of its lower end, a device forming at least one valve (21, 22). Device according to claim 1, characterized in that the intake device comprises a tube and in that said device forming at least one valve is placed in the axis of said tube. Device according to claim 1, characterized in that said intake device comprises a cylindrical tube, said device forming at least one valve, is placed on the cylindrical walls of said intake device. Separation device according to one of claims 1 to 3, characterized in that said intake device comprises an intake duct (7) coaxially surrounding the intermediate production tube (6) and the pump (3), said duct intake being extended by a separation duct (8) circumferentially provided with orifices (9) and held around said tubular column (2) by a fixing piece (16) Separation device according to claim 4, characterized in that the intermediate production tube (16) and the pump (3) are held coaxially with the intake duct by centralizers (10). Separation device according to claim 1, characterized in that the device forming at least one valve comprises a shutter, such as a ball or a valve (21), constantly stressed by elastic means (22) blocking an opening for introducing fluid (23) into the intake duct. Separation device according to claim 6, characterized in that the elastic means (22) have a compression resistance at a minimum pressure, said minimum pressure corresponding to a level of liquid in the intake duct above the pump. Separation device according to any one of Claims 1 to 7, characterized in that the intake duct (7) and the separation duct (8) are held in the well drilled by stabilizers (11). Separation device according to any one of Claims 1 to 8, characterized in that the length of the fluid intake device (7, 8) is chosen so as to develop a pressure difference of a few bars between the level of inlet of the pump (3) and the level of the orifices (9) for introducing the fluid into said device. Pumping installation in a drilled well comprising a separation device according to any one of claims 1 to 9, characterized in that said well comprises a low zone whose orientation varies from vertical to a strong inclination.

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