NO325285B1 - Method and system for selectively controlling actuation of a plurality of source tool assemblies - Google Patents

Description

The present invention generally relates to operations carried out and equipment used in connection with wells in the underground and produces, in an embodiment described here, a method and a system for hydraulically controlling actuation of downhole tools.

It is very advantageous to be able to independently control well tools from the surface of the earth, or another remote location. For example, production from one or more zones intersected by a well can be stopped due to water invasion, while production continues from other zones. Alternatively, one zone may be connected to a production pipeline, while other zones are shut off.

To control several downhole tools, various systems have been launched and used. One type of system uses electrical signals to select from among a plurality of well tools for operation of the selected tool or tools.

Another type of system uses pressure pulses in hydraulic lines, where the pulses are counted by the individual tools, to select specific tools for operation thereof.

In addition, WO-A] 00/09855 mentions a hydraulic control system where a certain combination of hydraulic pressure lines are pressurized for selective actuation of a specific well tool, such as one or more downhole valves, in a given way, i.e. open or closed. However, pressure pulses are used in the hydraulic lines as communication control signals for the well tool, so that independent actuation of several well tool devices is not possible.

Unfortunately, these systems are subject to fundamental disadvantages. The systems that use electrical communication or power to select or actuate a downhole tool typically have temperature limitations for the electrical circuits or are subject to conductivity and insulation problems, especially where integrated circuits are used or connectors are exposed to well fluids. The systems that use pressure pulses are typically very complex and therefore expensive to produce and difficult to maintain.

From the above it is understood that it would be highly desirable to produce a well control system which does not use electricity or complex pressure pulse counting mechanisms, but which provides a reliable, simple and cost-effective device for controlling downhole tools. It is thus an aim of the present invention to produce such a well control system and an associated method for controlling well tools.

In carrying out the principles of the present invention, according to an embodiment thereof, a well control system has been produced which allows flexible control and regulation with the actuation of well tool assemblies in a well. The system allows independent control of individual well tool assemblies. Associated methods have also been developed.

In one aspect of the present invention, there is provided a method for selectively controlling actuation of a plurality of well tool assemblies, comprising: positioning said plurality of well tool assemblies in a well,

interconnecting first and second hydraulic lines to each well tool assembly, characterized by the following steps: selecting a first one of the well tool assemblies for actuation thereof by generating a predetermined first fluid pressure on at least the second hydraulic line, and

actuating the first well tool assembly by generating a second fluid pressure on the first hydraulic line, wherein the second fluid pressure is greater than the first fluid pressure.

In another aspect of the present invention, there is provided a system for selectively actuating a plurality of well tool assemblies with a plurality of hydraulic lines connected to a plurality of well tool assemblies in a well, characterized in that each of the hydraulic lines is connected to an actuation control module at each of the well tool assemblies ,

where each actuation control module includes a selection device and a fluid measuring device,

where each selection device compares pressure on a second one of the hydraulic lines with a reference pressure source, where the corresponding well tool assembly is selected when the pressure in the second hydraulic line is greater than the reference pressure by a corresponding first predefined amount, and

where each fluid measuring device transfers fluid from the second hydraulic line to an actuator at the corresponding well tool assembly as a reaction to alternating pressure increases and pressure drops on a first one of the hydraulic lines when the corresponding well tool assembly is selected.

The selection device compares the pressure on one of the hydraulic lines with a reference pressure source. The well tool assembly associated with the selection device is selected when the pressure on the hydraulic line is greater than the reference pressure by a predetermined amount, but deviates from the reference pressure by less than another predetermined amount. The predetermined sizes can be determined by means of pressure limiting valves in the selection device interconnected between the hydraulic line and the reference pressure source.

The fluid measuring device transfers fluid from the hydraulic line to an actuator at the associated well tool assembly as a reaction to alternating pressure increases and pressure drops on another of the hydraulic lines. The fluid transfer function is only performed when the well tool assembly is selected.

At least two hydraulic lines and a reference pressure source are connected to the control module. A selection device at the control module includes two valves interconnected in series between one of the hydraulic lines and a fluid measuring device at the control module. One of the valves opens when the pressure on the hydraulic line is greater than a reference pressure by a first predetermined magnitude, and the other valve closes when the pressure on the hydraulic line is greater than the reference pressure by a second predetermined magnitude.

The fluid measuring device includes two pumps. One of the pumps transfers fluid from a first hydraulic line to an actuator at the well tool assembly in response to fluctuations in pressure on a second hydraulic line, and the other pump transfers fluid from the second hydraulic line to the actuator in response to fluctuations in pressure on the first hydraulic line.

In each case, the fluid is transferred via a different output at the control module, so that the actuator can be operated in a chosen way by selecting which of the pumps is to be used. Selection of the pump to be used is achieved by simultaneously applying a greater pressure to one of the hydraulic lines compared to the other hydraulic line after the well tool assembly is selected.

Each of the pumps includes a measuring chamber with a known volume. A known volume of fluid can thus be transferred to the actuator to produce a known displacement of a piston in the actuator.

These and other features, advantages, advantages and purposes of the present invention will become clear to the person skilled in the art by a careful review of the detailed description of representative embodiments of the invention that follows here and the accompanying drawings. FIG. 1 is a schematic diagram of a method for selectively controlling the actuation of downhole tools, the method incorporating the principles of the present invention; FIG. 2 is a schematic view of a first device usable in the method in FIG. 1, where the first device includes the principles of the present invention, and the first device is shown in a configuration prior to a well tool belonging to the device being selected for actuation thereof; FIG. 3 is a schematic view of the first device shown in a configuration following the selection of the well tool for actuation of this in a first way; FIG. 4 is a schematic view of the first device shown in a configuration after the well tool is deselected; FIG. 5 is a schematic diagram of the first device shown in a configuration following the selection of the well tool for actuation thereof in a second way; FIG. 6 is a schematic view of a second device usable in the method of FIG. 1, wherein the second device incorporates the principles of the present invention; FIG. 7 is a schematic diagram of a third device usable in the method in FIG. 1, where the third device incorporates the principles of the present invention. FIG. 1 is a representative illustration of a method 10 that incorporates the principles of the present invention. In the following description of the method 10 and other devices and methods described herein, directional terms such as "above", "below", "upper", "lower", etc. are used only for the sake of simplicity with reference to the accompanying drawings. In addition, it should be understood that the various embodiments of the present invention that are described here can be used in various ori-

entries, such as beveled, inverted, horizontal, vertical, etc. and in various configurations, without thereby deviating from the principles of the present invention.

In method 10, a plurality of well tool assemblies 12, 14, 16, 18 are positioned in a well. As shown in FIG. 1, each of the well tool assemblies 12, 14, 16, 18 includes a well tool 20, an actuator 22 for operation of the well tool (not visible in FIG. 1, see FIG. 2-7) and an actuation control module 24. The well tool 20 for each of the assemblies 12,14,16,18 which are representatively illustrated in FIG. 1 is shown as a valve, where the valves are used in the method 10 to control fluid flow between the formations or zones 26,28, 30, 32 which are cut through by the well and a pipe string 34 in which the tool assemblies are interconnected. However, it should be understood that other types of well tools and well tool assemblies can be used without deviating from the principles of the present invention, and it is not necessary for the well tool assemblies to be interconnected in a pipe string or for the well tool assemblies to be used to control fluid flow.

Each of the tool assemblies 12,14,16,18 is connected by hydraulic lines 36, 38 which extend from a hydraulic control unit 40 at the earth's surface or other remote location. The hydraulic control unit 40 is of the type well known to the person skilled in the art which is capable of regulating fluid pressure on the hydraulic lines 36, 38. The control unit 40 can be operated manually or with the help of computers, etc., and can also perform other functions.

The tool assemblies 12,14,16,18 are preferably "Interval Control Valves" commercially available from Halliburton Energy Services, Inc. and well known to those skilled in the art, which are useful for regulating fluid flow rates therethrough in the event of flow throttling. That is, each of the valves 20 can variably limit fluid flow through it, instead of only allowing or preventing fluid flow through it, so that an optimal flow rate for each of the zones 26, 28, 30, 32 can be established independently. To vary the obstruction in the fluid flow, the "Interval Control Valve" includes a flow throttling element that is moved by means of a hydraulic actuator, such as the actuator 22 shown schematically in FIG. 2-7.

Referring now in addition to FIG. 2 is an actuation control module 42 which includes the principles of the present invention representatively illustrated interconnected between two hydraulic lines 44,46 and the actuator 22. The control module 42 can be used for any of the control modules 24 in the method 10, in which case the hydraulic lines 44 ,46 would correspond to the hydraulic lines 36, 38 shown in FIG. 1, and the actuator 22 would correspond to an actuator in any of the well tools 20. However, it should also be clearly understood that the control module 42 can be used in other methods and the actuator 22 can be of a different type of well tool, without thereby deviating from the principles of the present invention.

f

The control module 42 includes a selection device 48 and a fluid measuring device 50. The selection device 48 senses fluid pressure on the hydraulic line 46 and determines whether the control module 42 is selected for actuation by its corresponding actuator 22. This determination is achieved by comparing the pressure on the hydraulic line 46 with a reference pressure source 52.1 this embodiment, and in the case where the control module 42 is used in the method 10, the reference pressure source 52 is an annular volume in the well external to the pipe string 34. The selection device 48 thus compares the pressure on the hydraulic line 46 with the hydrostatic pressure in the annular volume 52 to determine whether the control module 42 is selected for operation by its corresponding actuator 22.

To carry out this determination, the selection device 48 includes two changeover valves 54, 56 and two pressure limiting valves 58, 60. The shift valve 54 is normally open and loaded towards the open position by means of a spring 62. A similar spring 64 loads the shift valve 56 to a normally closed position. Only when both shift valves 54, 56 are open, fluid flow is permitted from the hydraulic line 46 to the fluid measuring device 50 for operation of the actuator 22. The control module 42 is thus selected for operation of its corresponding actuator 22 when both shift valves 54, 56 are open.

Fluid pressure on the hydraulic line 46 loads a shuttle 66 in the valve 56 to the left as seen in FIG. 2, which is towards an open position for the valve. However, in order for the shuttle 66 to move to the left, the pressure on the hydraulic line 46 must overcome the load force exerted by the pressure in the annulus 52 and open the pressure limiting valve 60. That is, the pressure on the hydraulic line 46 must be somewhat greater than the pressure in the annulus 52 plus the pressure limiting valve's 60 pressure limit. The pressure limiting valve 60 is thus used in the control module 42 to set a lower pressure limit by which the pressure on the hydraulic line 46 must exceed the pressure on the annulus 52 in order for the control module to be selected. FIG. 4 shows the configuration of the control module 42 when the pressure on the hydraulic line 46 has exceeded the pressure in the annulus 52 plus the pressure limit of the pressure limiting valve 60, where the shuttle 66 is moved to the left and opens the valve 56.

In a similar manner, the shift valve 54 includes a shuttle 68 which is moved to the left as seen in FIG. 2 to close the valve. Pressure on the hydraulic line 46 must overcome the pressure on the annulus 52 plus the pressure limit of the pressure limiting valve 58 in order for the shuttle 68 to be moved to the left. The pressure limiting valve 58 is thus used in the control module 42 to set an upper pressure limit by which the pressure on the hydraulic line 46 must not exceed the pressure on the annulus 52 in order for the control module to be selected.

In order for the control module 42 to therefore be selected, the pressure on the hydraulic line 46 must exceed the pressure in the annulus 52 plus the pressure limitation valve 60 pressure limit, and must not exceed the annulus pressure plus the pressure limitation valve 58 pressure limit. One will easily understand that by varying the pressure limits of the pressure limiting valves 58, 60, different control modules 42 can be configured to have different pressure ranges at which the individual control modules are selected. For example, the control module 24 in the tool assembly 12 in the method 10 can be configured to be selected when the pressure on the hydraulic line 38 is between 3448 kPa (500 psi) and 6895 kPa (1,000 psi) greater than the pressure in the annulus 52, the control module in the tool can the assembly 14 is configured so that it is selected when the pressure on the hydraulic line 38 is between 10342 kPa (1,500 psi) and 13790 kPa (2000 psi) greater than the annulus pressure, etc. Each of the well tool assemblies 12,14,16,18 can thus be independently selected by simply to vary the pressure on the hydraulic line 38.

The fluid measuring apparatus 50 readily responds to a difference between the pressures on the hydraulic lines 44,46 to move a round slide valve 70 between a configuration where fluid is measured from the hydraulic line 46 in response to alternating fluid pressure increases and drops on the hydraulic line 44, and another configuration where fluid is measured from the hydraulic line 44 in response to alternating fluid pressure increases and decreases on the hydraulic line 46. Thus, after the control module 42 has selected a suitable pressure on the hydraulic line 46, pressure is varied on one of the hydraulic lines 44,46 to transfer fluid from the second hydraulic line to the actuator 22. The hydraulic line on which the pressure is alternately increased and decreased determines whether a piston 72 in the actuator 22 is gradually moved to the right or to the left as seen in FIG. 2.

Movement of the piston 72 in increments is particularly useful where, as in method 10, the actuator 22 is included in a well tool assembly used to variably limit fluid flow therethrough. That is, an incremental movement of the piston 72 can be used to incrementally vary the fluid flow rate through any of the tool assemblies 12,14,16,18, so that the flow rate can be optimized for each of the associated zones 26,28,30, 32.

FIG. 5 shows the configuration of the control module 42 when the module is selected (that is, pressure on the hydraulic line is within the range defined by the pressure limiting valves 58, 60) and the pressure on the hydraulic line 46 exceeds the pressure on the hydraulic line 44. Note that a round slide 34 "spool" in the valve 70 is moved to the left as seen in FIG. 5. FIG. 3 shows a configuration of the control module 42 when the module is selected and pressure on the hydraulic line 44 exceeds pressure on the hydraulic line 46. Note that the circular slide 74 is moved to the right as seen in FIG. 3.

Referring to the configuration of the control module 42 as shown in FIG. 3, it should first be noted that with the circular slide 74 moved to the right, the hydraulic line 44 is in fluid communication with a fluid measuring chamber 78 with a floating piston 80 therein. The metering chamber 78 is also in fluid communication with the hydraulic line 46 via a check valve 82, which allows flow from the hydraulic line 46 to the metering chamber, but prevents flow from the metering chamber to the hydraulic line 46. A spring 84 biases the piston 80 upwardly, in one direction to draw fluid into the measuring chamber 78 from the hydraulic line 46.

An outlet in the measuring chamber 78 is also in fluid connection with one side of the piston 72 in the actuator 22. It will be easily understood that when pressure above the piston 80 overcomes the pressure below the piston in the measuring chamber 78 plus the loading force of the spring 84, the piston 80 will move downwards, and fluid in the chamber will be forced into the actuator 22 to thereby move the piston 72 to the right as seen in FIG. 3. Since the measuring chamber 78 has a known volume, the amount of fluid transferred from the measuring chamber to the actuator 22 is known and produces a known displacement of the piston 72.

To transfer the fluid from the measuring chamber 78 to the actuator 22, pressure on the hydraulic line 44 is increased so that it exceeds the pressure on the hydraulic line 46 (and thus moves the circular slide 74 to the right), and is further increased until the load force of the spring 84 is overcome and the piston 80 is moved downwards . To transfer additional fluid, the pressure on the hydraulic line 44 is reduced to thereby allow the spring 84 to move the piston 80 upwards and draw additional fluid into the metering chamber 78 from the hydraulic line 46.1 this step should not reduce pressure in the hydraulic line 44 to a level where it is less than the pressure in the hydraulic line 46, or the round slide 74 will move to the left.

The pressure on the hydraulic line 44 is then increased again so that the load force of the spring 84 is overcome and the piston 80 is again moved downwards, thereby transferring the fluid into the actuator 22. It will be easy to understand that the measuring chamber 78, the piston 80, the spring 84 and the non-return valve 82 form a pump that is sensitive to and responsive to pressure fluctuations in the hydraulic line 44 to transfer fluid from the hydraulic line 46 to the actuator 22.

To then consider the configuration of the control module 42 as shown in FIG. 5 (that is, the control module 42 is selected and the pressure on the hydraulic line 46 exceeds

the pressure on the hydraulic line 44 as described above), it should be noted that, with the round slide 74 moved to the left, the hydraulic line 46 is in fluid communication with a fluid measuring chamber 76 with a floating piston 86 therein. The metering chamber 76 is also in fluid communication with the hydraulic line 44 via a check valve 88, which allows flow from the hydraulic line 44 to the metering chamber, but prevents flow from the metering chamber to the hydraulic line 44. A spring 90 biases the piston 86 upwardly, in one direction to draw fluid into the measuring chamber 76 from the hydraulic line 44.

An outlet from the measuring chamber 76 is also in fluid connection with one side of the piston 72 in the actuator 22. It will be easy to see that when the pressure above the piston 86 overcomes the pressure below the piston in the measuring chamber 76 plus the loading force of the spring 90, the piston 86 will move downwards, and fluid in the chamber will be forced into the actuator 22 to thereby move the piston 72 to the left as seen in FIG. 5. Since the measuring chamber 76 has a known volume, the amount of fluid transferred from the measuring chamber to the actuator 22 is known and produces a known displacement of the piston 72.

In order to transfer the fluid from the measuring chamber 76 to the actuator 22, the pressure on the hydraulic line 46 is increased so that it exceeds the pressure on the hydraulic line 44 (thereby moving the circular slide 74 to the left), and is further increased until the load force of the spring 90 is overcome and the piston 86 moved downwards. In this step, the pressure on the hydraulic line 46 should not be increased to a level where it is outside the range of the control module 42 to select pressure established by means of the selection device 48.

To transfer additional fluid, the pressure on the hydraulic line 46 is reduced thereby allowing the spring 90 to move the piston 86 upward and draw additional fluid

into the measuring chamber 76 from the hydraulic line 44.1 this step the pressure on the hydraulic line 46 should not be reduced to a level where it is less than the pressure on the hydraulic line 44, or the round slide 74 would move to the right and the pressure on the hydraulic line 46 should not be reduced to a level where it is outside the control module 42's selection pressure range determined by means of the selection device 48.

Pressure on the hydraulic line 46 is then increased again so that the loading force of the spring 90 is overcome and the piston 86 is again moved downwards, thereby transferring the fluid into

the actuator 22. It will be readily understood that the measuring chamber 76, the piston 86, the spring 90 and the check valve 88 form a pump which is sensitive to and responds to pressure fluctuations in the hydraulic line 46 to transfer fluid from the hydraulic line 44 to the actuator 22.

Referring again to FIG. 1 is a preferred mode of selectively actuating the well tool assemblies 12,14,16,18 and increasing the pressure on both hydraulic lines 36,38, until the pressure is within the selection pressure range of at least one of the control modules 24. Note that more than one control module 24 can be selected at the same time, if desired, depending on the pressure limits of the pressure limiting valves in the control module selection device In addition, it should be noted that selection of the control module or control modules 24 can be achieved by using pressure applied to only one of the hydraulic lines 36, 38 ( for example, the hydraulic line 46 in the control module 42 in the embodiment shown in Figures 2-5), if desired.

Pressure in one of the hydraulic lines 36, 38 is then made greater than pressure on the other of the hydraulic lines to thereby determine the mode of operation for the associated actuator. The pressure in the hydraulic line 36 or 38 (whichever has the greater pressure therein to determine the mode of operation of the actuator) is then alternately increased and decreased thereby transferring known volumes of fluid incrementally from the other hydraulic line to the actuator, to produce incremental displacements of a piston in the actuator.

In addition, now referring to FIG. 6, there is representatively illustrated an alternative configuration in which the pressure reference source is an accumulator 92 instead of the annulus 52 shown in FIG. 2-5. The accumulator 92 is connected to the pressure limiting valves 58, 60 instead of the connection to the annulus 52. In addition, a throttle 94 and a non-return valve 96 allow fluid flow between the accumulator 92 and the hydraulic line 46, so that the accumulator is continuously equalized with the hydrostatic pressure in the hydraulic line 46 , but the pressure in the hydraulic line 46 can be increased to move the valves 54, 56 if desired. For this purpose, the throttle 94 allows only a very gradual equalization of pressure between the hydraulic line 46 and the accumulator 92.

Referring now in addition to FIG. 7, there is representatively illustrated an alternative configuration where the pressure reference source is a third hydraulic conduit 98, instead of the annulus 52 shown in FIG. 2-5. The hydraulic line 98 is connected to the pressure limiting valves 58, 60 instead of the connection to the annulus 52. The hydraulic line 98 constitutes a further advantage in that the pressure on the hydraulic line 98 can be varied at a remote location to thereby influence the pressure areas on the hydraulic line 46 with which the control module 42 is selected. The hydraulic line 98 can, for example, be connected to the hydraulic control unit 40 in the method 10 as shown in FIG. 1.

It should be understood that other types of reference pressure sources can be used instead of the annulus 52, the accumulator 92 and the hydraulic line 98, without thereby deviating from the principles of the present invention.

After a careful review of this description of representative embodiments of the invention, one skilled in the art will readily understand that many modifications, additions, substitutions, and other changes can be made to the specific embodiments, and that such changes are covered by the principles of the present invention. The description is to be understood as an illustration and examples where the scope of the invention is limited only by the attached claims.

Claims (29)

1. Method for selectively controlling actuation of a plurality of well tool assemblies, comprising: positioning said plurality of well tool assemblies in a well, connecting first and second hydraulic lines to each well tool assembly, characterized by the following steps: selecting a first one of the well tool assemblies for actuation thereof by generating a predetermined first fluid pressure on at least the second hydraulic line, and actuating the first well tool assembly by generating a second fluid pressure on the first hydraulic line, wherein the second fluid pressure is greater than the first fluid pressure. 2. Method according to claim 1, characterized by the step of selecting a second one of the well tool assemblies for actuation thereof by generating a predetermined third fluid pressure on at least the second hydraulic line. 3. Method according to claim 2, characterized by the step of actuating the second well tool assembly by generating a fourth fluid pressure on the first hydraulic line, where the fourth fluid pressure is greater than the third fluid pressure. 4. Method according to claim 1, characterized in that the actuation step further includes transferring fluid from the second hydraulic line to an actuator at the first well tool assembly as a reaction to generation of the second fluid pressure on the first hydraulic line. 5. Method according to claim 1, characterized in that the actuation step further includes alternating pressure on the first hydraulic line between the first and second fluid pressures, thereby incrementally moving a piston in an actuator at the first well tool assembly. 6. Method according to claim 1, characterized in that the actuation step further includes alternating pressure on the first hydraulic line between the first and second fluid pressures, thereby repeatedly measuring a known volume of fluid from the second control line to an actuator at the first well-tool assembly . 7. Method according to claim 1, characterized in that the selection step further includes comparing the first fluid pressure with a pressure in an annulus in the well about the first well tool assembly. 8. Method according to claim 7, characterized in that in the selection step, the first well tool assembly is selected when the first fluid pressure is greater than the annulus pressure by a predetermined amount or size. 9. Method according to claim 7, characterized in that in the selection step, the first well tool assembly is selected when the first fluid pressure is within a predetermined pressure range, where a lower limit in the pressure range is greater than the annulus pressure by a predetermined amount. 10. Method according to claim 1, characterized in that the selection step further includes comparing the first fluid pressure with a pressure in an accumulator. 11. Method according to claim 10, characterized in that in the selection step, the first well tool assembly is selected when the first fluid pressure is greater than the accumulator pressure by a predetermined size or amount. 12. Method according to claim 10, characterized in that in the selection step, the first well tool assembly is selected when the first fluid pressure is within a predetermined pressure range, where a lower limit in the pressure range is greater than the accumulator pressure by a predetermined size or amount. 13. Method according to claim 1, characterized in that the selection step further includes comparing the first fluid pressure with a pressure in a third hydraulic line connected to each of the well tool assemblies. 14. Method according to claim 13, characterized in that in the selection step, the first well tool assembly is selected when the first fluid pressure is greater than the pressure in the third hydraulic line by a predetermined size or amount. 15. Method according to claim 13, characterized in that in the selection step, the first well tool assembly is selected when the first fluid pressure is within a predetermined pressure range, where a lower limit of the pressure range is greater than the pressure in the third hydraulic line by a predetermined amount or size . 16. System for selectively actuating a plurality of well tool assemblies with a plurality of hydraulic lines connected to a plurality of well tool assemblies in a well, characterized in that each of the hydraulic lines is connected to an actuation control module at each of the well tool assemblies, where each actuation control module includes a selection device and a fluid measuring device, where each selection device compares pressure on a second one of the hydraulic lines with a reference pressure source, where the corresponding well tool assembly is selected when the pressure in the second hydraulic line is greater than the reference pressure by a corresponding first predefined amount, and where each fluid measuring device transfers fluid from the second hydraulic line to an actuator at the corresponding well tool assembly as a reaction to alternating pressure increases and pressure drops on a first one of the hydraulic lines when the corresponding well tool assembly is selected. 17. System according to claim 16, characterized by the areference pressure source being an annulus placed around the corresponding well tool assembly in the well. 18. System according to claim 16, characterized in that the reference pressure source is an accumulator. 19. System according to claim 18, characterized in that the reference pressure in the accumulator is equalized by the pressure in the other hydraulic line. 20. System according to claim 16, characterized in that the reference pressure source is a third one of the hydraulic lines. 21. System according to claim 16, characterized in that each well tool assembly is deselected for actuation thereof when the pressure in the second hydraulic line exceeds the reference pressure by a corresponding second predetermined quantity or size. 22. System according to claim 16, characterized in that each fluid measuring device includes a measuring chamber, where the chamber releases a known fluid volume from there to the corresponding actuator when the corresponding well tool assembly is selected for actuation thereof and pressure on the first hydraulic line is increased, and that the chamber receives therein the known fluid volume from the second hydraulic line when the corresponding well tool assembly is selected for actuation thereof and pressure on the first hydraulic line is lowered. 23. System according to claim 16, characterized in that each fluid measuring device transfers fluid from the first hydraulic line to the actuator at the corresponding well tool assembly in response to alternating pressure increases and drops on the second hydraulic line when the corresponding well tool assembly is selected. 24. System according to any one of claims 16 to 23 characterized by an actuation control module for selective actuation of a well-tool assembly in a well, first and second hydraulic lines and a reference pressure source placed in the well, where the control module comprises: a fluid measuring device, and a selection device which includes first and second valves are interconnected in series between the second hydraulic line and the fluid measuring apparatus, wherein the first valve opens when the pressure on the second hydraulic line is greater than a reference pressure by a first predetermined amount, and the second valve closes when pressure on the second hydraulic line is greater than the reference pressure by a second predetermined magnitude or amount. 25. System according to claim 24, characterized in that the fluid measuring device includes a first pump which transfers fluid from the second hydraulic line via the first and second valves to a first output in the control module as a reaction to alternating pressure increases and pressure drops in the first hydraulic line. 26. System according to claim 25, characterized in that the fluid measuring device further includes a second pump which transfers fluid from the first hydraulic line to a second output in the control module as a reaction to alternating pressure increases and pressure drops in the second hydraulic line. 27. System according to claim 25, characterized in that the first pump includes a measuring chamber, where each increase in pressure on the first hydraulic line causes an emptying of a known fluid volume from the measuring chamber to the first outlet, and where each pressure drop on the first hydraulic line causes that a known fluid volume is received in the measuring chamber from the other hydraulic line. 28. System according to claim 25, characterized in that the pressure in the first hydraulic line varies between a first pressure approximately equal to the pressure in the second hydraulic line and a second pressure greater than the pressure in the second hydraulic line in order to transfer fluid from the second hydraulic line to the first exit. 29. System according to claim 24, characterized in that the fluid measuring apparatus includes a circular slide valve which selectively interconnects the first and second hydraulic lines with first and second pumps in the fluid measuring apparatus, where the circular slide valve has a first configuration where the first pump transfers fluid from the second hydraulic line to a first output in the control module in response to pressure fluctuations in the first hydraulic line, wherein the first configuration is selected in response to the pressure in the first hydraulic line being greater than the pressure in the second hydraulic line, and wherein the rotary valve has a second configuration wherein the second pump transfers fluid from the first hydraulic line to a second output in the control module as a reaction to pressure fluctuations in the second hydraulic line, where the second configuration is selected as a reaction to the pressure in the second hydraulic line being greater than the pressure in the former st hydraulic line.