EP0892886B1 - Installation for pumping a two-phase liquid/gas effluent - Google Patents

Abstract

The invention concerns a pumping installation designed for being mounted in an oil well extending from the surface to a layer of oil-bearing rock, comprising a pipe column at the lower end of which is mounted a pump, a joint, mounted in the well around the pipe column and delimiting a chamber at the lower end of the well, in which is arranged a pump. The installation further comprises a hydro-ejector, in the pipe column, including a lower pressure zone opening into the upper end of the chamber.

Description

The present invention relates to an installation pumping a two-phase liquid / gas effluent and, more particularly to such an installation intended for pumping of hydrocarbons from an oil well.

In some oil wells, the natural flow hydrocarbons from the bottom to the surface is insufficient to allow or maintain commercial production. This is due either to the viscosity and the weight of the effluents, or to too low a natural pressure at the bottom of the well, in look at the factors that oppose their elevation towards the area. In order to allow the production of the well at a commercial scale a system should be used artificial elevation of the effluent, or system well activation. For example, you can mount a pump at the lower end of a production tube located in the well, or an injection facility can be provided gas at the bottom of the well. The latter type of installation, plus commonly called "gas lift", used to lighten the column of hydrocarbons located in the well to facilitate its ascent to the surface.

A gas injection installation at the bottom of the well is generally reliable, but has the drawback of require, on an isolated site, a gas source under pressure, for example a compressor and its piping associated.

The use of a pump, arranged at the end bottom of a casing through which the effluent rises biphasic liquid / gas on the surface, presents disadvantages when this effluent contains a proportion significant gas. The bubbles contained in the effluent are compressible, a fraction of the pump energy serving to compress the gas and not to send the fluid to the area. This phenomenon can even lead to the flow of pumped fluid becomes zero (situation commonly called "Cavitation" or "gas-lock"). Centrifugal pumps are particularly prone to gas lock, especially in wells due to their location at the foot of a column fluid which, due to its own weight, opposes their back pressure, even at zero flow, back pressure hydrostatic. In addition, on the occasion of judgments of flows, gases and liquids end up separating by gravity at the bottom of the well, which in some cases creates serious pump malfunctions during restart if the accumulated gas gets into the pump, or if, due to this transient regime, a large gas bubble may have formed inside the pump.

It is therefore advisable to separate most of the gas from the liquid phase of the effluent before this liquid is sucked by the pump. So all the energy of the pump can be devoted to sending the liquid to the surface and risks of cavitation are reduced.

But this separation of gas upstream of the pump requires a different gas discharge channel than that borrowed by the liquid passing through the pump. One way common to perform this function is to let the gas get "Ventilate" - that is to say walk - through space ring that exists between the inner wall of the casing of the well and the external wall of the casing which is used for the flow pumped liquid. However, this method presents several major disadvantages which result in making the more expensive or even dangerous operation of the well: including the loss of natural elevation energy; chemical and / or mechanical attack on materials contact with gas; and significant heat exchanges and uncontrollable between the effluents and the perimeter of the wells which can cause costly flow problems.

To partially overcome these drawbacks, the document FR-A-2.723.143 describes an installation for wells tanker with a pump arranged at the end bottom of a first casing, a second casing being intended to receive, where appropriate, gas from the effluent and separated upstream of the pump, and to conduct it up to the surface regardless of the liquid phase According to this document in order to promote the separation of gas from the effluent at the bottom of the well, the pump is fitted with a shirt, which extends to a level below the layer of petroleum rock. So the entering effluent in the well is forced to descend before being aspirated by the pump, which has the effect of ensuring excellent separation of the gas intended to pass through the casing independent.

The installation described in document FR-A-2.723.143, although it allows the pump to receive a effluent with low gas content, however present disadvantages in that it requires a second casing along the entire length of the well, which creates significant dimensional and economic constraints of the work. In addition, the liquid effluent column raised to the surface by the pump is heavy since it is substantially gas-free, which requires a pump greater power.

The subject of the present invention is therefore a pumping system for a two-phase liquid / gas effluent which is simple, robust and reliable, and which is not subject to the drawbacks mentioned above.

To achieve this objective, the present invention offers a pumping installation intended to be mounted in a well extending from the surface to a layer of petroleum rock, including casing at the end bottom of which is mounted a pump, a seal, mounted in the well around the casing and delimiting a chamber the lower end of the well, in which is disposed the pump, characterized in that the installation comprises, plus, a hydro-ejector in the casing comprising an area depression opening in the upper end of the bedroom.

• la figure 1 est une vue en coupe longitudinale d'une installation selon un premier mode de réalisation de l'invention, et
• les figures 2a et 2c sont des vues schématiques de trois modes de fonctionnement de l'invention.

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

• FIG. 1 is a view in longitudinal section of an installation according to a first embodiment of the invention, and
• Figures 2a and 2c are schematic views of three modes of operation of the invention.

As shown in Figure 1, a well tanker 10 extends between the surface (not shown) and a layer of petroleum rock 12. The well is provided with perforations 14, opening in the oil-bearing rock, which allow the flow of the hydrocarbon effluent to the interior of the well 10. The well 10 includes a casing 16 which makes it waterproof compared to the layers of rock crossed by the well. Inside the well a casing 18 extends between the surface and a point a few meters above the rock layer 12. Casing 18 has at its lower end a pump 20 provided of inputs 22 for the effluent to be sent to the surface. In the example shown, the pump 20 is centrifugal rotary and its engine is powered from the surface by a electric cable (not shown). Before being sucked by the pump 20, the effluent coming from the rock layer 12, which fills the well to a level 24, moves into the direction of the arrows 26. During this movement, the gas contained in the effluent is released and rises in the well up to the level of a joint 28, more commonly called "packer", thus forming a gas pocket 30 between the level 24 of the liquid effluent and the seal 28, in a chamber 31 defined in well 10 below packer 28. The pump 20 may advantageously include a special separator to baffle or dynamic centrifugal or vortex type in order to better guarantee separation upstream of the pump (not represented. Without such a separator, separation takes place usually by gravity in room 31 where find, at a relatively low speed taking into account the section of their passage, the raw effluents leaving the perforations.

The packer 28 defines an annular chamber 33 delimited by the internal wall of the casing 16 and the wall external of the casing 18 between the seal 28 and the surface. The packer 28 prohibits effluents and in particular gas from enter room 33. They cannot cross the part superior to the well than by borrowing the casing 18. The room 33 and all the accessories it contains such as the power cable of the pump 20 are therefore preserved mechanical and chemical attack and remains available for other functions such as for example reception a heat-insulating substance to insulate casing 18.

At the gas pocket 30, the casing 18 comprises a liquid-gas hydro-ejector 32, or venturi, intended to create a depression area inside 34 by venturi effect. The liquid-gas hydro-ejector 32 comprises orifices 36 connecting the area of depression 34 and the gas pocket 30.

When switching on the installation of pumping described above, the pump 20 is set in motion, sucking liquid effluent through inlets 22 and the driving back, in the direction of arrow 38, towards the surface. The passage of the effluent through the liquid-gas hydro-ejector 32 creates a depression in its interior due to its converging geometry, depression causing the suction through the orifices 36 of the gas from the gas pocket 30 in the direction of the arrows 40. In the interior of the hydro-ejector, the gas is then entrained by the liquid effluent from pump 20 to which it mixes and recombines, thus reducing the column of effluent contained in the casing 18, thus facilitating its ascent to the surface.

As the gas pocket 30 is still in communication with the casing 18 through the orifices 36; 44, the formation of a gas pocket extending to the pump 20 is avoided, even during a prolonged shutdown of the installation. This results in preventing the pump from restarting when surrounded by gas.

Figure 2a shows schematically the normal configuration of flows, corresponding to that described above with reference to Figure 1. The modes of operation of the invention shown in Figures 2B and 2C have additional features allowing the installation to react better in transient or transient degraded situations, and make it more efficient and effective.

FIG. 2A shows schematically the characteristics of the installation of figure 1. The liquid discharged by pump 20 in the direction of the arrow 38, draws gas into the hydro-ejector 32 in the direction of the arrow 40. The mixture of the recombined liquid with the gas is sent to the surface by the casing 18 in the direction of the arrow 50.

Figure 2B schematically represents the situation where, in an installation according to the invention, the pump 20 sucks effluent with a high proportion of gas or contains large gas bubbles in its impellers. Centrifugal pumps do not tolerate gas bubbles well not being adapted to repress such effluents. It is therefore wise to facilitate the evacuation of these bubbles towards pump output before continuing to send the effluent to the surface.

Indeed, the presence of large gas bubbles inside the pump 20 can occur despite the separation of the gas upstream before the fluids enter pump 20, due for example to a degassing complementary to inside the pump 20, or during a phase transient operation such as a restart of installation. To avoid such a situation extends and becomes stationary at the expense of material which would overheat and from the production of the well which would null, the invention proposes to relieve the repression of the pump 20 with, on the one hand, a non-return valve 52 in the tubing 18 between the pump 20 and the hydro-ejector 32 for prohibit the return of effluents to pump 20 and support the weight of hydrostatic column, and, on the other share, a lateral opening 54 located under this valve and allowing the lateral evacuation of the formed effluents essentially gas to the annular chamber 31. This valve 52 and the lateral opening 54 are preferably systems that can be set up and removed from the well at cable by an operation commonly called "wire-line" in order to make their maintenance inexpensive. We can by example use equipment housed in "pockets" of the type commonly used for gas injection valves for column relief effluent and commonly called "side-pocket". The lateral opening 54 must close as soon as a certain liquid effluent flow and higher pressure, will again reached when pump 20 is discharged. operation of this lateral opening 54 may be either controlled from the surface using a command line electric or hydraulic depending on parameters available on the surface, or be automatically piloted locally with for example the discharge pressure of the pump 20, there is the pressure difference due to friction the effluent between the inlet and the outlet of the opening lateral 54. This principle is used in gate valves security called "storm-choke".

As shown in Figure 2B, when the pump no longer sends liquid effluent to the surface, the column of liquid present in the casing 18, downstream of the hydro-ejector 32 flows, under the effect of its own weight, and up to equilibrium, through the holes 36 fitted in the hydro-ejector to chamber 31. Once that the casing has emptied to equilibrium, the gas present in chamber 31 can rise to the surface in entering the casing 18 through the orifices 36. Thus, even if the level 24 of the liquid effluent has gone down in below the level of pump 20, this purging of gas in the chamber 31 allows the level of liquid 24 to rise to the beyond that of pump 20. Once the pump again found immersed in liquid effluent having a low proportion of gas, sending the effluent to the surface can start again.

FIG. 2C schematically represents a installation intended to alleviate the problems which can occur when the level 24 of the liquid exceeds that of the hydro-ejector 32.

Such a situation occurs if the hydro-ejector has a gas suction capacity greater than the gas flow rate released by the separation located upstream from the entrance to the pump 20. This is even the most likely situation in the normal configuration of the installation according to the invention. Even if the hydro-ejector is capable of operating in liquid-liquid as is the general case in "jet-pumping" », It is better to avoid training number of liquid from chamber 31 by the liquid effluents flowing in the direction of arrow 38. Because such training would reduce performance and / or the efficiency of the system. To avoid this training liquids, and make selective training with respect to gas and liquid from chamber 31 several solutions are proposed below: the first is based on the fact that the hydro-ejector 32 is more or less capable of performing this selection naturally by "hydraulic blocking". This is the phenomenon that plays when in jet pumping liquid-liquid, the jet makes a "gas-lock", ie can no longer entrain liquid. This condition is obtained for a sufficient flow of liquid Student. The second consists in using a float intended for close the lateral gas inlet of the hydro-ejector 32 when liquid from chamber 31 lifts it. This float here again would be a system that could fish out the cable and which could for example be installed in a "Side-pocket", through which all the gas from the pocket 30 before entering the hydro-ejector 32. The third, also cable recovery, would be the equivalent of the float but with a different technology, for example, clapper or other “storm choke” closing in the process We can also provide a small hole diameter or "duse" with little resistance to gas flow and much to that of liquids, even causing the degassing of these latter.

The liquid-gas hydro-ejector 32, and the accessories corresponding to the functions shown in Figures 2B and 2C as well as the movable element of the pump are advantageously arranged to allow their ascent to the cable surface when maintenance is required.

The liquid-gas hydro-ejector can be mounted in the casing at a point above the joint, the area of depression communicating with the room by a conduit which crosses the joint.

Claims (5)

1. Pumping installation for fitting in a well (10) extending from the surface to a layer of oil-reservoir rock, comprising a casing (18) at the lower end of which a pump (20) is mounted, a seal (28; 42), fitted in the well round the casing (18) and delimiting a chamber (31) at the lower end of the well, in which chamber (31) the pump is disposed, characterised in that the installation also comprises a hydro-ejector (32), in the casing (18), comprising a negative pressure zone (34) which opens into the upper end of the chamber (31).
2. Installation according to claim 1, characterised in that the liquid/gas hydro-ejector (32) is fitted in the casing (18) directly below the seal (28), the negative pressure zone (34) communicating with the chamber (31) via orifices (36) made in the liquid/gas hydro-ejector.
3. Installation according to claim 1, characterised in that the liquid/gas hydro-ejector (32) is mounted in the casing (18) at a point above the seal (42), the negative pressure zone (34) communicating with the chamber (31) via a conduit (46) traversing the seal (42).
4. Installation according to any of claims 1 to 3, characterised in that the pump also comprises a centrifugal separator communicating with the negative pressure zone (34) of the liquid/gas hydro-ejector (32).
5. Installation according to any of claims 1 to 4, characterised in that it also comprises a check valve (52) fitted in the casing (18) between the pump (20) and the hydro-ejector (32), and a lateral aperture (54) in the casing (18) between the pump (20) and this check valve (52).

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