NO310694B1 - Method and apparatus for intermittent oil production by means of a mechanical interface device - Google Patents

Description

The invention relates to a method and device for promoting artificial oil lift in oil-producing wells, as stated in the non-characterizing parts of claims 1 and 7.

The invention aims to promote the artificial lifting of oil that collects in an oil well. Two interconnected production tubes (tubing) are used plus an extremely flexible mechanical interface device, which removes the oil that accumulates in the production tubes, pushing it to the surface and consequently reducing the hydrostatic pressure exerted by the hydrostatic head on the producing area.

After an oil well has been completed, the flow of oil to the surface will only occur if the reservoir pressure is sufficient to overcome the back pressure exerted by the height of the oil accumulated in the production pipe.

If the reservoir pressure is not sufficient to overcome this back pressure, it will be necessary to use some artificial lifting method to send the oil further to the surface. Some examples of such methods include mechanical pumping systems, downhole centrifugal pumping systems and progressive cavity pumping systems.

A common feature of all these systems is that they require the supply of some type of energy to drive the pumping equipment, which is usually located around the producing area, which establishes the need to utilize some physical device to supply energy. This energy supply device may be an electrical cable to feed the motor of a submerged centrifugal pump, or a string of mechanical rods to drive a submersible pump or a progressive cavity pump. All these systems share the common feature that they consist of a large number of components that are prone to failure.

One method that has been used to a large extent is pneumatic pumping, known to those skilled in the art as "gas lifting"; which basically consists of injecting gas into the annulus that exists between the production pipes and the well's casing. Gas is injected into the production pipe using special valves with the aim of gasifying the oil. This gasification reduces the oil's specific weight and facilitates the flow of oil further up to the surface.

There are essentially two "gas lift systems", namely "continuous gas lift" and "intermittent gas lift".

With the continuous gas lift system, as the name suggests, gas is continuously injected into the annulus until it reaches a valve at the bottom of the well which allows the gas to be injected into the production pipe.

5 With the "intermittent gas lift", as described in US patent no. 5-211,242, the well, in contrast to the continuous one, is allowed to produce for some time without gas being injected. Gas is then injected into the annulus at fairly high pressures. Special valves installed in the gas lift mandrel allow the gas to be injected into the production pipe which thus

provides the effect of pumping the oil to the surface.

10

Despite certain advantages, the artificial gas lifting methods have some serious disadvantages, such as, for example, slipped between the gaseous and liquid phases, giving rise to a situation where the gas flows to the surface and the oil remains in the interior of the well, which

is very common in wells that produce high-viscosity oil.

15

Another serious disadvantage is that it is difficult to apply such a technique in awiks wells where the slope of the well can enable the formation of gas segregation zones (airlock) which can even make the use of

the procedure. The great depth of the producing area is another feature of the well that inhibits the utilization of the gas lift method.

US patent no. 5,006,046 describes a method and a device for removing liquid from a well using pressurized gas in the wellbore, injected through a

U-shaped tube. Although said US patent provides an artificial gas lifting method at a low cost, it does not provide a solution to the disadvantages, such as the slippage between the gas and liquid phases and the formation of gas segregation zone.

Another serious disadvantage of the artificial gas lift methods is the increase in pressure

bottom, which is a further limiting factor in oil production.

30

Yet another solution to the problem, as described in US Patent No. 3,894,814, is the utilization of the method known as "plunger lift"; it consists mainly of using some kind of plunger to cause the oil in the production pipe to rise. 35 Gas is injected into the bottom of the well and this causes the plunger to rise to the wellhead. As it moves upward, the plunger pushes the oil accumulated in the string in front of it, causing the oil to flow up.

Although this method shows good results, it has the serious disadvantage that it is necessary to close the valves which are on the surface at the moment the plunger reaches its highest position, so as to enable the plunger to descend to the bottom of the well again for to start a new cycle. This causes interruptions in production and limits the application of the method to wells at shallow depths, as the waiting time for the plunger to move down in deeper wells would be very long.

Another method uses synthetic rubber balls to provide flow of the oil accumulated in the production pipe. This method, known to the experts as the "spherical pump gas lift system", essentially consists of utilizing a second string called the pressurizing string, with a diameter identical to the production pipe. This second string is used to move the balls or spheres down. The two production pipes are connected in a zone close to the producing area.

This method has certain disadvantages and the main objection is the danger that the balls may get stuck or be retained in the strings. Another disadvantage is due to the fact that the efficiency of the method depends fundamentally on the sealing ability of the balls which, taking into account their actual geometry, do not guarantee a perfect seal.

A further problem to be considered is the high cost of the balls which wear out in a short time. Another problem is the complexity of the facilities on the surface and those below the surface.

The present invention proposes a method and a device which solves all the shortcomings described above.

The present invention relates to a device and method for intermittent oil production using a mechanical interface device.

In a first aspect, the invention relates to a device for intermittent oil production by means of a mechanical interface device, which comprises: first and second production pipe strings extending inside a casing from a wellhead to a connection located down a well, at a producing area, said connection or coupling interconnecting the lower ends of each of said first and second production strings with a short production string extending further down the well and equipped with a check valve at its lower end • an equalization tank for receiving oil located at said wellhead, where the device is characterized by: • a gas source at the wellhead connected to each of said first and second production strings for the supply of gas under high pressure, where first and second gas supply valves are located between each of said first and second production strings and said gas source to selectively supply gas under high pressure to its respective production string; • that each of said first and second production strings is equipped in its upper change with a sending/receiving device with valve aids to allow introduction of a mechanical interface device into its respective production string; • that each of said first and second production strings is equipped respectively with first and second diverter devices which connect first and second upper connection points with first and second lower connection points, intended to facilitate an equalization of upstream pressure and downstream pressure when said mechanical interface device passes between said first or second upper connection points and said first or second lower connection points; • that each of said first and second diverter devices is equipped with first and second non-return valves to allow a gas flow to pass in one direction only; • that each of said first and second production strings is equipped with a first and second production line connected to an equalization tank production line, which is connected to said equalization tank; • that each of said first and second production lines for each of said first and second production strings is equipped with first and second production valves which, when open, allow oil to flow from their respective first or second production strings to said equalization tank; • a liquid/gas level sensor device located in said surge tank production line to detect when a flow from each of said first or second production strings to said surge tank consists mainly of injected gas and thus commands closure of the respective first and second gas supply valves and opening of the respective first and second production valves.

Preferred features of the device appear in claims 2-6.

In a second aspect, the invention relates to a method for the intermittent oil production by means of a mechanical interface device which uses the device described above and which is characterized in that it comprises the following steps: • opening of said first and second valve devices in order to enable the introduction of at least one of said mechanical interface device into one of said first and second sending/receiving devices and placement of said mechanical interface device between said first or second upper

connection point and said first or second lower connection point;

• opening of said first and second production valves while said first and second gas supply valves are kept closed so that oil can accumulate inside said

production pipe strings;

• closing said first and said second production valves and opening a respective first or second gas supply valve after a predetermined period of time, thereby using gas under high pressure from said gas source to push said interface device down into one of said first and second production strings, through said coupling, and up through the second of said at least first and second production string, thereby transferring oil from said first and second

production lines to said equalization tank;

• interrupting the upward movement of the mechanical interface device after its passage through said first or second lower connection point in said second of said at least first and second production strings to allow gas to flow through a respective diversion device to effect equalization of the upstream pressure and downstream pressure on the mechanical interface device located between said first or second connection point and said first or

second lower connection point on said second a said two production lines;

• the use of said liquid/gas interface sensor device to detect the exact moment at which the flow to said equalization tank is constituted, mainly of injected gas, to command the closing of the first or second gas supply valve opened at the start of the operation, thereby interrupting

the gas flow; and

• the use of said liquid/gas interface sensor to command the opening of the first or second production valve, which was closed at the beginning of the operation so as to enable the start of a new movement cycle of said mechanical interface device through said first and second production strings, now in an opposite direction .

Preferred features of the method appear in claim 8.

The present invention will be better described with reference to the attached drawings where: • Fig. la, lb and lc are schematic representations of a completed well that uses the conventional method known as "gas lift with pump balls". • Fig. 2 is a schematic representation of how to use the method and the device which is the subject of the invention in a completed oil well, with an expansion pack placed just above the producing area. • Fig. 3 is a representation of the method and device which is the subject of the invention in an oil well, using the use of an expansion pack located just above the producing area and the use of a line that lets gas into the annulus. • Fig. 4 shows a schematic representation of the application of the method and device which is the subject of the invention in a completed oil well without the use of an expansion pack. • Fig. 5 shows a schematic representation of the application of the method and the device which is the subject of the invention in an oil well where the lower end of the production pipes lies below the producing area.

Before describing the invention, reference is made to fig. la, lb and lc, where a schematic representation of the application of the gas lift method with a ball pump can be seen.

You can see the two strings 41 and 42, which are of the same internal diameter. The string 42 is called the injection string, and is intended for introducing balls and injecting gas. The string 41, referred to as the production string, is intended to drain away the produced oil as well as to release the balls or spheres.

In fig. it can be seen that a ball 45 has previously been introduced into the injection string 42 which rests on a constriction 43 which is located close to a producing area.

The portion of the injection string 42 which is between the constriction 43 and the surface contains gas at a pressure sufficient to cause the oil to rise, yet not sufficient to force the ball 45 through the constriction 43. The pressure in the production string 41 at this instant is equal to the separation pressure , as the valve 47 located on the surface is open.

At a given moment, the gas injection valve 44 opens, as shown in fig. lb, which allows the gas to pass into the injection string 42 and also cause the valve 47 to close.

At this moment, another ball 46 is released by a ball emitting/receiving device 52, located in the wellhead; it is fed into the injection string 42 with the gas flow and also gravity, until it arrives on top of the ball 45.

The pressure against the ball 45 increases continuously until it reaches a value sufficient to force it through the constriction 43, which takes it towards a bend 49 where a hydrostatic head 48 has already accumulated. When the ball 45 passes through the constriction 43, eventually the volume of gas held by this also passes through the constriction 43.

As can be seen from fig. lc, then closes the gas injection valve 44, which allows the valve 47 to open. The gas volume released into the injection string 42 at the opening of the injection valve 44 is held back, because the ball 46 prevents it from passing through the constriction 43. This gas volume held back in the injection string 42 will ensure the lifting of the oil in the next cycle.

At the same time, the expansion holds the gas released by the passage of the ball 45 through the constriction 43, pushing the ball 45 and consequently the hydrostatic head 48 as well, which takes it to the surface.

A bend 51 is designed so that the produced oil can flow out through a terminal 50 and so that the ball 45 can return to the ball emitting/receiving device 52.

This method has several shortcomings, including the fact that the equipment involved is very complicated and the consumption of balls is very high, in addition to the great danger of these balls getting stuck.

The invention which is the subject of the present application and claims proposes to use a first and a second production string to lift the die, which is connected at the bottom of the well. These production pipes can be of different diameters. At least one mechanical interface device runs along the two production strings, either in one direction or the other, pushed by the gas pressure, which thus causes the oil to flow out to the surface.

Fig. 2 shows the configuration of the equipment used for applying the method which is the subject of the invention, in a completed oil well with expansion packing 3 placed just above the producing area 2.

One sees a casing 1 with the first and second production strings 4, 4A inside. The production strings 4, 4A extend the wellhead of an oil well to a joint 8, which is the object that provides the connection between the first and second production strings and a short production pipe 6.

At the lower end of the short production tubing string 6 there is a check valve 7. The expansion pack 3 is located in a short string 6 at a location just above the producing area 2 and seals the annulus 32 around the first and second production strings 4, 4A, the short production string 6 and casing 1.

As a result of the application of the first and second production strings 4 and 4A, several surface components are used in pairs, which means that certain components appearing in one of the parts associated with one of the first and second production strings 4 and 4A, each must have an equivalent component in the second batch linked to the second production line, as both components perform one and the same function.

These common components will appear in the text identified by the same reference numerals, but one of them always with the letter "A" added, as was done with the first and second production strings 4, 4A. Thus, the surface components located in the portion associated with the string 4A and having their equivalents in the other portion associated with a string 4 will be identified by the same number plus the letter "A" added.

One can then see, while still referring to fig. 2, that there are a first and a second emitter/receiver 11, 11A with their respective first and second check valves 20, 20A, first and second production valves 15, 15A, first and second diverters (bypasses) 29, 29A, first and second valves 14, 14A, and first and second gas supply valves 18, 18 A.

A gas source 9 provides the high-pressure gas supply to be injected into the first and second production strings. The oil produced by the first and second production strings is taken by the pressure fluctuation line 21 to the pressure fluctuation tank, or equalization tank 17. One can further see the presence of a liquid/gas interface sensor 26 installed in the pressure fluctuation line 21 to sense the liquid/gas interface. This sensor has several rather important functions that will be clearly understood during the course of this description.

The method that is the subject of the present invention begins with the opening of one of the first and second valves 14, 14A at the respective first and second sending and receiving devices 11, 11 A, in order to be able to introduce at least one mechanical interface device 10, which can for example be a ball or plug, into the selected first or second sending/receiving device. This mechanical interface device 10 must be positioned between the first upper point 12 and the first lower point 13, or second upper point 12A and second lower point 13A on the conductors 29, 29A respectively, as shown in fig. 2.

The mechanical interface device 10 must be manufactured from a material that makes it very flexible in order to cause it to be displaced through the production lines.

Next, the first and second production valves 15 and 15A are opened, while the first and second gas supply valves 18 and 18A are closed. This step aims to collect oil in the first and second production strings 4 and 4A.

After a predetermined period of time, the mechanical interface device 10 is deployed. To do this, one of either the first and second production valves 15 or 15A is closed and one of either the first and second gas supply valves 18 or 18A is open; they must mandatorily be those installed in the same first or second protraction string 4, 4 A, where the mechanical interface device 10 was introduced. Thus, in the event that the mechanical interface device 10 has been introduced into the first transmitter/receiver 11, as shown in fig. 2, the first production valve 15 must be closed and the first gas supply valve 18 must be opened.

As the pressure in the gas coming from the gas source 9 is higher than the pressure in the oil which is in the first and second production strings 4, 4A, the mechanical interface device 10 is pushed by the gas into the interior of the production pipe string connected to the part where it was has been introduced, as the first or second check valves 20, 20A located in the first or second diverter 29, 29A block the passage of the gas, which prevents flow passage through this route.

Pushed by the gas, the mechanical interface device 10 descends along the entire length of the first or second production string 4, 4A until it reaches the coupling 8; it then initiates the oil lift through the second first or second production string 4A, 4, and causes displacement to the surface of the amount of oil accumulated in the two production pipe strings. The production line 21 leads the outgoing oil flow from the first or second non-return valves 20, 20A associated with the respective production string into the equalization tank 17.

The upward movement of the mechanical interface device 10 will be interrupted immediately after it has passed the first or second lower point 13A, 13, because at this very moment the gas starts to flow through the first or second diverter 29A, 29. This means that the upstream pressure and the downstream pressure for the mechanical interface device 10 become equal. The mechanical interface device 10 will then stop at the first or second sending/receiving device 11A, 11, located between the second upper point 12A and the second lower point 13A (or the first upper point 12 and the first lower point 13).

The liquid/gas interface sensor 26 installed in the pressure fluctuation line 21 detects the exact moment at which the outflow becomes only injected gas. At this moment, this sensor orders the closing of the first or second gas supply valve 18, 18A which was opened at the start of the operation, thereby interrupting the gas flow.

The liquid/gas interface sensor 26 also enables the opening of the first or second production valve 15, 15A which was closed in the first operational phase, thus enabling the start of a new filling cycle into the first and second production strings 4, 4A.

After the amount of oil has reached the correct level in the first and second production strings 4, 4A, a new cycle of passing the mechanical interface device 10 through the first and second production strings 4, 4A can begin, now in opposite directions, as described previously, i.e. if in the previous route production the first production valve 15 was closed, in the new route the second production valve 15A must instead be closed, etc., in order to continue with the operations in the normal way.

If it is desired to prevent the gas remaining in the first and second production strings 4, 4A after the execution of each lifting cycle, from exerting a back pressure that would inhibit the filling of these first and second production strings 4, 4A, one could use a gas discharge line 31 for gas discharge (fig. 3) to connect the pressure fluctuation line 21 with the annulus 32 in the well, so as to cause the gas accumulated in the first and second production pipes 4, 4A and in the line 21 into the annulus 32, as shown in fig. 3.

A discharge control valve 28 (Fig. 3) placed in the gas discharge line 31 also controlled by the sensor 26 monitors the gas discharge flow into the annulus 32. A check valve 27 prevents a possible backflow from the equalization tank 17 and from the production line 21 into the annulus 32.

Fig. 4 shows the equipment in a completed oil well without the use of the expansion gasket 3 and fig. 5 shows the equipment in an oil well where the producing area 2 is located above the short production string 6, a location that favors the application of the present method because it reduces the back pressure in the producing area, as the liquid phase continues to accumulate below it.

It should be noted that the application of the method according to the present invention is not hampered by the slope of the well in relation to the vertical, even in situations where extreme slopes occur, such as e.g. in an awikswell.

Various embodiments of the present invention have been presented, to highlight various applications. In all the situations shown in the figures, it can be seen that the basic equipment configuration used in the practice of the method is the same. It is important to emphasize that all the described embodiments have a generic illustrative character and must in no way be considered to limit the invention.

In order for the present invention to be effective, it is fundamental that the mechanical interface device 10 is sufficiently flexible to be able to easily move along the first and second production lines and along the surface equipment.

In this method, the mechanical interface device 10 that is used is made of low-density polyurethane foam which, due to its great flexibility, is considered to be the most adequate material.

However, other materials can also be used, provided they have the desired mechanical properties.

Claims (8)

1. Device for intermittent oil production by means of a mechanical interface device (10) comprising: • first and second production pipe strings (4, 4A) which extend inside a casing pipe (1) from a wellhead to a connection (8) located down a well, at a producing area (2); • said connection (8) interconnects the lower ends of each of said first and second production strings (4, 4A) with a short production string (6) which extends further down the well and is equipped with a check valve (7) at its lower end; and • an equalization tank (17) for receiving oil placed at said wellhead, where said device is characterized in that it further comprises: • a gas source (9) at the wellhead connected to each of said first and second production strings (4, 4A), for supplying gas under high pressure, where first and second gas supply valves (18, 18A) is placed between each of said first and second production strings (4, 4A) and said gas source (9) to selectively produce gas under high pressure to one of the first or second production string (4, 4A); • each of said first and second production strings (4, 4A) is respectively provided in its upper change with first and second sending/receiving devices (11, 1IA) with first and second valve auxiliaries (14, 14A) to allow the introduction of a mechanical interface device (10) into its respective first or second production string (4, 4A); • each of said first and second production strings (4, 4A) is produced respectively with first and second diverter devices (29, 29A) which respectively connect each of the first and second upper connection points (12, 12A) with the first and second lower connection points (13, 13A) intended to aid the equalization of upstream pressure and downstream pressure when said mechanical interface device (10) passes said first and second upper connection points (12, 12A) and said first and second lower connection point (13, 13A); • each of said first and second diverter devices (29, 29A) respectively is equipped with first and second non-return valves (20, 20A) to allow a gas flow to pass in one direction only; • each of said first and second production strings (4, 4A) is equipped with a production line connected to an equalization tank-production line (21), which is connected to said equalization tank (17); • each of said production lines for each of said first and second production strings (4, 4A) are respectively equipped with first and second production valves (15, 15A) which, when open, allow oil to flow from the first and second production strings (4 , 4A) to said equalization tank (17); • a liquid/gas surface sensor device (26) placed in said surge tank production line (21) to detect when a flow from each of said first or second production strings (4, 4A) to said surge tank (17) consists mainly of injected gas and which thus orders the closing of the respective first and second gas supply valves (18, 18A) and the opening of the respective first and second production valves (15, 15A). 2. Device according to claim 1, characterized in that it comprises an expansion gasket (3) which is located around a lower part of the short production pipe string (6) above said producing area (2), for sealing an annular space (32) between said first and second production strings (4, 4A) and said casing (1). 3. Device according to claim 1, characterized in that the producing area (2) is located above the short strand (6). 4. Device according to claim 1, characterized in that it comprises: • a gas discharge line (31) which connects the equalization tank production line (21) with the annulus (32) of the well; • a discharge valve (28) located in the line (31) and controlled by the liquid/gas interface sensor (26), to control discharge of the gas flow into the annulus (32); and • a non-return valve (27) located in the equalization tank-production line (21), between the equalization tank (17) and said gas discharge line's (31) connection point to said equalization tank-production line (21), to prevent a backflow of oil from said equalization tank ( 17) and into the annulus (32). 5. Device according to claim 2, characterized in that it comprises: a gas discharge line (31) which connects the equalization tank production line (21) with the annulus (32) of the well; a discharge valve (28) located in the line (31) and controlled by liquid/gas the interface sensor (26), to control discharge of the gas flow into the annulus (32); and a non-return valve (27) located in the equalization tank-production line (21), between the equalization tank (17) and said gas discharge line's (31) connection point to said equalization tank-production line (21), to prevent a backflow of oil from said equalization tank (17 ) and into the annulus (32). 6. Device according to claim 3, characterized in that it comprises: • a gas discharge line (31) which connects the equalization tank production line (21) with the annulus (32) of the well; • a discharge valve (28) located in the line (31) and controlled by the liquid/gas interface sensor (26), to control discharge of the gas flow into the annulus (32); and • a non-return valve (27) located in the production line (21), between the equalization tank (17) and said gas discharge line (31) connection point to said equalization tank-production line (21), to prevent a backflow of oil from said equalization tank (17) and into the annulus (32). 7. Method for intermittent oil production using a mechanical interface device (10) comprising: • first and second production tubing strings (4, 4A) which run inside a casing (1) from a wellhead to a connection (8) located down a well, at a producing area (2), wherein said connection (8) interconnects the lower ends of each of said first and second production strings (4, 4A) with a short production string (6) extending further down the well; • each of said first and second production strings (4, 4A) provided respectively in its upper end with a sending/receiving device (11, 11A) with first and second valve auxiliary devices (14, 14A) to allow the introduction of a mechanical interface device (10 ) into one of said first or second production lines (4, 4A); • a gas source (9) at the surface connected to each of said first and second production strings (4, 4A), for supplying gas under high pressure; • first and second gas supply valves (18, 18A) placed respectively between each of said first and second production strings (4, 4A) and said gas source (9) to selectively produce gas under high pressure to respective production strings (4, 4A); • an equalization tank (17) for receiving oil located at said wellhead; • each of said first and second production strings (4, 4A) is produced respectively with first and second production line with first and second production valves (15, 15A) and connected to an equalization tank production line (21) which is connected to said equalization tank (17); • each of said first and second production strings (4, 4A) is produced respectively with first and second diverter devices (29, 29A) which respectively connect each of the first and second upper points (12, 12A) with the first and second lower points (13, 13 A) intended to assist an equalization of upstream pressure and downstream pressure when said mechanical interface device passes between said first and second upper points (12,12A) and said first and second lower points (13,13A); • each of said first and second diverter devices (29, 29A) respectively is equipped with first and second non-return valves (20, 20A) to allow a gas flow to pass in one direction only, and a liquid/gas surface sensor device (26) located in said surge tank production line (21); where said method is characterized in that it comprises the following steps: • opening of one of the valves (14, 14A) so as to enable the introduction of at least one mechanical interface device (10) into one of the sending/receiving devices (11, 11A); • placement of such a mechanical interface device (10) between said first or second upper connection points (12, 12A) and said first or second lower connection points (13, 13A); • opening said first or second production valves (15, 15A) while said first and second gas supply valves (18, 18A) are kept closed so that oil can accumulate inside said production pipe strings (4,4A); • closing said first and said second production valves (15, 15 A) and opening a respective first or second gas supply valves (18, 18A) after a predetermined period of time, thereby using gas under high pressure from said gas source (9) to push said interface device (10) down into one of said first and second production strings (4, 4A), through said coupling (8), and up through the other of said at least first and second production strings (4, 4A), thereby moving oil from said first and second production lines (4, 4A) to said equalization tank (17); • interrupting the upward movement of the mechanical interface device (10) after its passage through said first or second lower connection point (13A, 13) in said second of said at least first and second production strings (4A, 4) to allow gas to flow through a first or second diverting device (29A, 29) to effect equalization of the upstream pressure and downstream pressure on the mechanical interface device (10) located between said first or second point (13A, 13) on said first and second production line (4A, 4); • the use of said liquid/gas interface sensor (26) to detect the exact moment at which the flow to said equalization tank (17) consists mainly of injected gas to order the closing of the first or second gas supply valve (18A, 18) which was opened at the start of the operation, thereby interrupting the gas flow; and • the use of said liquid/gas interface sensor (26) to command the opening of the first or second production valve (15, 15A), which was closed at the beginning of the operation so as to enable the start of a new movement cycle of said mechanical interface device (10) through said first and second production strings (4.4A), now in the opposite direction. 8. Method according to claim 7, characterized in that it comprises: • the use of said liquid/gas interface sensor device (26) to control a gas discharge control valve (28) installed on a gas discharge line (31), so that the gas which is in said first and second production tubing strings (4,4A) and in said gas discharge line (31) when the passage cycle of the mechanical interface device (10) is finished, can be discharged into an annulus (32) between said first and second production strings (4, 4A) and said casing (1 ): • place a non-return valve in said gas discharge line (31) to prevent the oil from flowing back from the equalization tank (17) into the annulus (32).