(19)
(11)EP 2 536 915 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
26.06.2019 Bulletin 2019/26

(21)Application number: 11744226.9

(22)Date of filing:  21.02.2011
(51)International Patent Classification (IPC): 
E21B 34/10(2006.01)
E21B 43/20(2006.01)
(86)International application number:
PCT/CA2011/000194
(87)International publication number:
WO 2011/100834 (25.08.2011 Gazette  2011/34)

(54)

MAGNETS-BASED TOOL FOR PULSING INJECTED LIQUID

WERKZEUG AUF MAGNETBASIS FÜR EINE GEPULST INJIZIERTE FLÜSSIGKEIT

OUTIL POURVU D'AIMANTS POUR INJECTER UN LIQUIDE PAR IMPULSIONS


(84)Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

(30)Priority: 19.02.2010 GB 201002854

(43)Date of publication of application:
26.12.2012 Bulletin 2012/52

(73)Proprietor: Wavefront Reservoir Technologies Ltd.
Cambridge, ON N1T 1J8 (CA)

(72)Inventor:
  • LEFEBVRE, Lance Leo
    Edmonton, Alberta T5K 1Z6 (CA)

(74)Representative: Dentons UK and Middle East LLP 
One Fleet Place
London EC4M 7WS
London EC4M 7WS (GB)


(56)References cited: : 
WO-A1-2007/036722
WO-A1-2009/132433
SU-A1- 1 035 202
US-A1- 2005 260 089
US-A1- 2009 193 908
WO-A1-2007/100352
JP-U- H01 180 068
US-A- 5 297 631
US-A1- 2008 271 923
  
      
    Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


    Description


    [0001] This technology relates to injection of a liquid, typically water, into a borehole in the ground. Creating pulses in the injected liquid can be effective to increase the penetration of the liquid for greater distances radially outwards from the borehole, and can also be effective to reduce fingering, and to homogenize the permeability of the ground around the borehole.

    BACKGROUND



    [0002] Liquid is supplied to the pulsing tool, typically from a reservoir at the surface. A pressurized volume of the liquid is contained in an accumulator, which may be regarded as including the volume contained in the pipe or conduit leading down, from the surface, to the pulse-tool.

    [0003] The pulse-tool includes a pulse-valve, through which liquid passes from the accumulator into the formation when the pulse-valve is open. That flow is blocked when the pulse-valve is closed. Thus, the formation-pressure is rising when the pulse-valve is open, and the formation-pressure is falling when the pulse-valve is closed, when the just-injected liquid dissipates into the ground. Likewise, the accumulator-pressure is falling when the pulse-valve is open, and is rising (i.e the accumulator is recharging) when the pulse-valve is closed.

    [0004] The frequency and magnitude of the pulses is affected by the back-pressure of the ground formation around the borehole. The formation-pressure rises/falls, and the accumulator-pressure falls/rises, when the pulse-valve is open/closed.

    [0005] The pulse-valve operates automatically in response to changes in these pressures, and particularly in response to the changing differential pressure between the accumulator-pressure and the formation-pressure, herein termed the PDAF. When the pulse-valve is closed, the PDAF increases towards its high-threshold; when the pulse-valve is open, the PDAF decreases towards its low-threshold. The pulse-valve automatically cycles open-closed-open-closed-etc, so long as the conditions are such that the PDAF cycles between its high- and low-threshold levels.

    [0006] The designers seek to open the pulse-valve very rapidly, because the resulting burst of energy can create a shock-wave that assists the pulse in travelling large distances through the ground. The more explosively the pulse-valve can open, the greater the energy of the resulting shock-wave, and the greater its penetration.

    [0007] US2009/193908 discloses a magnetic flow controller which transforms a slow reduction in pressure of fluid flow over time to a measurable fluid flow.

    [0008] US2008/271923 discloses a device and method and/or system for generating pulses to improve drilling rates, the ability to drill straighter and farther or fracturing or injection efficiencies in a geological formation that may contain desirable hydrocarbons.

    [0009] US2005/260089 discloses a method of transmitting pressure pulses from a downhole location through a flowing fluid in a wellbore comprising using a linear actuator to controllably move a reciprocating member axially back and forth between a first position and a second position to at least partially obstruct flow of the flowing fluid to generate the pressure pulses.

    SOME FEATURES OF THE INVENTION



    [0010] In the technology depicted herein, the differential pressure PDAF is applied in such manner as to urge a pulse-valve member to move to the pulse-valve-open position. Resisting this PDAF-induced force on the valve-member is a force arising from the contact, or near- contact, of a pair of permanent magnets. When the PDAF reaches its high-threshold, the magnets break apart, and the pulse-valve opens.

    [0011] As the magnets move apart, the force urging them together drops very quickly, and this is a characteristic that favours rapid opening of the pulse-valve.

    [0012] Preferably, the magnets are immersed in an oil-bath, which protects the magnets from contact with liquid-borne metal particles.

    DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS



    [0013] The technology will now be further described with reference to the accompanying drawings, in which (all the drawings being cross-sectioned side-elevations):

    Fig.1 shows a portion of a pulse-tool.

    Fig.2 shows the pulse-tool installed in a well-bore in the ground.

    Fig.3A shows a fixed housing of another pulse-tool.

    Fig.3B shows a movable-unit corresponding to the housing of Fig.3A.

    Fig.4A shows the movable-unit assembled into the fixed housing, in a pulse-valve-closed condition.

    Fig.4B is the same view as Fig.4A, but shows the pulse-valve open.

    Fig.5 shows an alternative oil-bath arrangement.

    Fig.6A shows a fixed-housing of a further pulse-tool.

    Fig.6B shows a movable hammer component, corresponding to the housing of Fig.6A.

    Fig.6C shows a movable valve-seat component, corresponding to the housing of Fig.6A.

    Fig.7A shows the assembled pulse-tool from Figs.6A,6B,6C in a pulse-valve-closed condition.

    Fig.7B is the same view as Fig.7A, showing the pulse-valve about to open.

    Fig.7C is the same view as Fig.7A, showing the pulse-valve open.

    Fig.8A is the same view as Fig.7A, showing the pulse-valve starting to close.

    Fig.8B is the same view as Fig.7A, showing the pulse-valve more nearly closed.

    Fig.8C is the same view as Fig.7A, showing the pulse-valve still more nearly closed.

    Fig.9A shows yet another pulse-tool, in the pulse-valve-closed condition.

    Fig.9B is the same view as Fig.9A, showing the pulse-valve about to open.

    Fig.9C is the same view as Fig.9A, showing the pulse-valve fully open.



    [0014] The pulse-tool 20, shown in its closed position in Fig.1, is for use in conjunction with apparatus for injecting a liquid into a well-bore in the ground. The liquid is supplied from a surface station (Fig.2), where the liquid is stored in a pressurized container or accumulator 23. Supply-tubing 25 extends down the well-bore to the pulse-tool 20. The supply-tubing 25 can be regarded as part of the accumulator.

    [0015] The pulse-tool 20 is equipped with exit-ports 27, through which the liquid is forced out of the pulse-tool. The ejected liquid enters the annular space 28 between the pulse-tool 20 and the well-casing 29. From there, the liquid enters the ground-formation 30, via perforations 32 in the casing 29.

    [0016] In some cases, a packer (e.g an inflatable packer 34) is provided to close off the annular space above the perforations 32; and another packer can be placed below the perforations, if required. In other cases, there is no packer, and liquid from the surface-station is injected into the annular space 28. In that case, the liquid enters the formation in a continuous stream, whether the pulse-valve is open or closed. The pulse-tool 20 is used to impress pulses on the continuous stream. When a packer is used, the flow of liquid is blocked, more or less completely, and no liquid enters the ground formation when the pulse-valve is closed.

    [0017] In Fig.1, the pulse-valve 36 includes a movable valve-member 38, which is in engagement with a valve-seat 40. The valve-seat 40 is formed in the fixed housing 41 of a valve-section 43 of the tool 20. A rubber seat-seal 45 seals the pulse-valve 36 closed at this time. The movable valve-member 38 is a component of a movable-unit 47.

    [0018] Another component of the movable-unit 47 is a movable magnet 49, which is press-fixed into a magnet-cup 50. A fixed magnet 52 is similarly press-fixed into the fixed housing 41 of the pulse-tool 20. The movable magnet 49 is dimensioned such that, when the movable magnet 49 is assembled into the magnet-cup 50, a lip of the magnet-cup 50 protrudes slightly (e.g 0.1mm), beyond the face of the movable magnet 49. The presence of the protruding lip ensures that the two magnets 49,42 cannot actually touch together.

    [0019] The movable unit 47 is subjected to the supply pressure of the accumulator 23 on its upwards-facing surfaces. The movable unit 47 is subjected to the pressure in the ground formation 30 on its downwards-facing surfaces. Thus, the movable unit 47 is subjected to a pressure differential equal to the difference between the accumulator pressure and the formation pressure, measured at the depth of the exit-port 27. This differential is herein termed PDAF.

    [0020] When the pulse-valve 36 is open, liquid flows out of the accumulator 23 into the formation 30. The accumulator pressure is falling and the formation pressure is rising, and thus the PDAF is decreasing, when the pulse-valve is open. The pulse-valve is designed to close when the PDAF falls to a low-threshold.

    [0021] When the pulse-valve 36 is closed, the accumulator 23 is replenished, and so the accumulator pressure is rising. At the same time, recently injected liquid dissipates into the formation, and so the formation pressure is falling. Therefore, the PDAF is increasing when the pulse-valve 36 is closed. The pulse-valve is designed to open when the PDAF reaches a high-threshold.

    [0022] The high-threshold and low-threshold magnitudes of the PDAF, at which the pulse-valve 36 opens and closes, are determined by the designers, the thresholds being a function of the pressure-exposed areas of the movable-unit 47 and of the strength of the magnets 49,52.

    [0023] When the pulse-valve is closed (Fig.1) the accumulator pressure acts downwards on the unit 47 over the upwards-facing pressure-exposed area A1 of the movable valve-member 38, and the formation pressure acts upwards over an equal down-facing area. Thus, the force driving the unit 47 downwards, when the pulse-valve is closed, equals the (rising) magnitude of PDAF multiplied by the area A1. The force driving the unit 47 upwards is the attractive force arising from the magnets 49,52. The high-threshold is reached when the rising PDAF force equals the magnetic attraction force.

    [0024] When this happens, the magnets 49,52 start to separate. Thus, the movable-unit 47 starts to move downwards. After a few millimetres of downward movement, the valve-member 38 moves clear of the seat-seal 45, and the pulse-valve opens.

    [0025] At this point, the magnets being now separated, the attractive force between the magnets has now decreased. Therefore, the difference between the PDAF-force (acting downwards) and the magnet-force (acting upwards) has increased considerably.

    [0026] The result is that the movable-unit 47 now slams downwards. Thus, the pulse-valve changes from closed to full-open very rapidly indeed. It may be regarded that the pulse-valve opens explosively.

    [0027] The contrast between the opening of the present magnet-controlled pulse-valve and, for example, a coil-spring-controlled pulse-valve will now be considered. When the valve is biased closed by magnetic attraction, and the magnets start to separate, the attractive force between them starts to fall. When the valve is biased closed by a coil-spring, and the coil-spring starts to deflect, the spring force starts to rise.

    [0028] A coil-spring has a positive spring-rate. That is to say: the force required to further deflect a coil-spring increases as the deflection of the coil-spring increases. By contrast, magnets in attraction have a negative spring-rate. That is to say: the force required to further separate a pair of magnets decreases as their separation increases. (It may be noted that, if the valve were to be biased closed by magnetic repulsion, the spring-rate then would be positive, like a coil-spring.)

    [0029] The negative rate is desirably advantageous in the case of a valve which is biased closed, but has to open explosively. Furthermore, while the spring-rate of a coil-spring is linear, the spring-rate of a pair of magnets, arranged for attraction, is markedly non-linear; that is to say, the decrease in attraction force as the magnets separate from zero (or almost zero) to the first millimetre is a much greater decrease than the decrease in force as the magnets separate e.g from the fourth millimetre to the fifth millimetre. (With magnets, in fact the incremental decrease in attraction force is proportional to the square of the separation distance.) This non-linearity is also desirably advantageous in the case of a valve that has to be biased closed against a large pressure differential, but has to open explosively.

    [0030] The pulse-valve 36 remains open, and liquid pours out into the formation, until the PDAF has fallen to its low threshold. Even though the pulse-valve is wide open, the PDAF does not fall to zero. Liquid flows through the valve at a large flowrate, and in fact, the operators see to it that the flowrate is so large that there still is a significant pressure drop through the pulse-valve even though the pulse-valve is wide open. Furthermore, the flowing liquid undergoes a change in the direction of its momentum vector as it passes through the valve, in that downwards momentum of the flowing liquid is lost as the liquid acquires radially-outwards velocity. Diverting the momentum vector imparts a downwards force on (the conical upper surface of) the movable-unit 47.

    [0031] As the outwards flow of liquid slows down, however, the PDAF-force, and the dynamic reaction force on the valve-member, both decrease, and eventually the low-threshold of the PDAF is reached, in which the downward force on the movable unit 47 is low enough that it can be overcome even by the weak attraction of the now-spaced-apart magnets 49,52.

    [0032] When the low-threshold level of the PDAF is reached, the magnets start to move together. As they do so, their attraction force increases. So, the closing movement, which at first was gradual, becomes more rapid until finally the valve is fully closed.

    [0033] The negative spring-rate of the magnets therefore gives rise to the characteristic that the pulse-valve closes rapidly, as well as opening explosively. In turn, this means that the pulse-valve can be regarded as bistable, being significantly unstable at intermediate points between open and closed, whereby it is (almost) impossible for the pulse-valve to become hung up at an intermediate point. This is an advantageous characteristic from the standpoint of maintaining performance over a long service life.

    [0034] Fig.3A shows the fixed housing 341 of another pulse-tool 320. Fig.3B shows the movable-unit 347 of that tool. Figs.4A,4B show the movable-unit assembled into the fixed housing. The pulse-tool 320 operates in the same way as the pulse-tool 20, in that the closed pulse-valve opens when the PDAF reaches its high-threshold, and closes when the PDAF reaches its threshold. The pulse-valve 336 in Figs.4A,4B has no rubber seal, but rather the seal is formed by the tight fit of the valve-member 338 in the valve-seat 340.

    [0035] Of course, some leakage will occur when the pulse-valve 336 is closed, as in Fig.4A. However, that is not detrimental. As far as the pulses are concerned, it is the rapidity with which the pulse-valve 336 opens from almost-closed to full open, that is important in energizing the pulse. The more violently the pulse-valve opens, the more energetic the pulse. The pulse-valve then remains wide open until the PDAF decreases to its low-threshold.

    [0036] Figs.3A,3B,4A,4B also show an oil-bath 356, in which the magnets 349,352 are completely immersed. The oil-bath 356 is contained between an upper oil-seal 358 and a lower oil-seal 360. The two oil-seals 358,360 are of the same diameter, so that, as the movable-unit 347 moves up/down, the volume of the oil-bath remains the same. However, the shape of the volume changes as the unit 347 moves, and the oil moves between the different chambers of the volume through the centre conduit 361 of the movable-unit 347.

    [0037] Oil is injected (during assembly of the tool) into the oil-bath through a bottom check-valve 363. Another check-valve 365 is provided at the top of the oil-filled volume, which functions as a pressure relief valve. The oil fills up the spaces and chambers between the upper and lower oil-seals 365,363. That is to say, when the oil-bath has been filled and pressurized, oil emerging from the top check-valve 365 witnesses that fact, and indicates also that all the air has been bled out of the oil-filled volume.

    [0038] If it should happen that the pressure of the oil in the oil-bath 356 drops to a low magnitude, the bottom check-valve 363 opens, and admits a quantity of water from the ground formation into the oil-bath. Also, if it should happen that the oil in the oil-bath should expand, such that the pressure inside the oil-bath rises, the top check-valve permits the excess pressure to blow off. In fact, these check-valves 363,365 open very rarely during operational service, but they can be useful when the tool is brought to the surface, in ensuring that there is little or no excess pressure in the oil-bath, which might be a safety hazard.

    [0039] The oil-bath 356 provides lubrication for the moving parts. However, a major function of the oil-bath is to keep the magnets clean. Powerful magnets attract small particles of ferrous and other magnetic material, of which there is an all-too-copious supply in down-hole tools and equipment - deriving both from the tool itself and from being carried down via the liquid being injected. If the magnets were allowed to come in contact with the injected liquid, they would become coated with magnetic debris in a very short time. The oil-bath prevents this magnetic debris from actually touching the magnets.

    [0040] Preferably, the upper 358 and lower 360 seals of the oil-bath should be exposed to the same pressure, and preferably both to the formation pressure. Of the dynamic seals in the tool, the oil-bath seals should seal perfectly, since the oil should not leak out. By contrast, the dynamic seals separating the formation pressure from the accumulator pressure, including the seal of the pulse-valve, can generally be allowed to leak slightly, and the expression "closed" in relation to the pulse-valve should be construed accordingly.

    [0041] An alternative oil-bath arrangement is shown in Fig.5. The oil-bath is enclosed by the volume defined between the two oil-seals 558,560. The movable-unit 547 is guided by bearings 566. The oil is in contact with the upper face of a piston 562, the lower face of which is exposed to formation pressure. Thus, the pressure of the oil is always equalized to the formation pressure. Thus, both sides of the two oil-seals 558,560 are exposed, effectively, to formation pressure, which helps to minimize seal-friction. Preferably, in fact, a bias-spring 564 helps ensure that the oil-pressure (slightly) exceeds the external pressure.

    [0042] It may be noted that the assembly shown in Fig.5 - like that of the other oil-baths shown herein - is self-contained, and can remain intact during routine resettings and adjustments of the pulse-tool; the assembly can also be removed, still with the oil-bath intact, from the rest of the tool, e.g for bench-servicing of the oil-bath components.

    [0043] The magnets 349,352 are annular-cylindrical in shape. In the example, the magnets are rare-earth magnets, being of grade-N52 neodymium-iron-boron permanent magnet material. The fact that such magnets lose power at elevated temperatures is not significant, because, even if there were a tendency for the tool to become heated, the tool is constantly being bathed in the (cool) liquid being injected.

    [0044] The magnets are mechanically pressed into their housings. As mentioned, the housings have lips 354, which protrude slightly beyond the surface of the magnet, which prevents the magnets themselves from making contact. The magnets and their nickel plating are very brittle and might chip upon impact.

    [0045] In the size of magnet likely to be selected in a down-hole tool of the kind as described herein, the attractive force between two magnets, when close together, can be expected to be in the order e.g of 500newtons. At a separation of ten mm, typically the force has dropped to 140N, at fifteen mm to 92N, and at twenty mm to 63N.

    [0046] The pulse-valve 336 is fully open when the bottom end of the movable-unit 347 contacts the nose 367 of the fixed housing 341 (Fig.4B). The designers can make this distance adjustable if so desired. They can add cushioning if the impact is troublesome.

    [0047] As mentioned, where the full travel of the movable unit is e.g fifteen mm, it can be expected that a magnetic attraction of 500N (when the magnets are (almost) together) will have dropped to 92N. The designers might consider this force to be too small to ensure that the movable-unit will move sharply upwards (the PDAF having reached its low-threshold) with the required degree of certainty and reliability. If so, they can incorporate a spring, e.g a coil-spring 369 into the nose 367, as in Fig.3A, such that the bottom end of the movable-unit engages the coil-spring 369 as it nears its full downwards travel stroke.

    [0048] The added coil-spring 369 makes the effective aggregate spring-rate of the forces acting on the movable-unit 347 now positive (or at any rate makes the spring-rate less negative), whereby, in the example, the force urging the movable-unit 347 upwards, at the fifteen mm point, can be e.g 150N (or such other magnitude as the designers may decide) instead of the 92N.

    [0049] In order to increase, still further, the rapidity of the opening of the pulse-valve, the movable-unit can be formed as two separate components, which are movable relative to each other. In one version of a divided movable-unit, the valve-seat is arranged to be movable.

    [0050] Fig.6A shows the fixed-housing 641, to which the fixed magnet 652 is attached; Fig.6B shows what may be termed a movable hammer component 670 of the movable-unit 647, to which the moving magnet 649 is attached; and Fig.6C shows the other movable component of the movable-unit 647, namely a movable valve-seat 672.

    [0051] Fig.7A shows these components assembled and in their pulse-valve-closed positions. Fig.7B shows the two movable components 670,672 of the movable-unit 647 moving downwards together, in unison, whereby the pulse-valve 636 remains closed. In Fig.7C, the motion of the movable valve-seat 672 has been arrested, while the movable hammer 670 has continued downwards, whereby the pulse-valve 636 has now opened.

    [0052] In Fig.7A, the hammer 670 is in its uppermost position, being held there by the fact that the magnets 649,652 are (almost) touching, being held slightly apart, as mentioned, by the slightly-protruding lip of the magnet-cup (not shown in Fig.7A.)

    [0053] The upwards-facing surfaces of the movable valve-seat 672 are exposed to accumulator-pressure, while its downwards-facing surfaces are exposed to formation-pressure. The same is true of the hammer 670. The PDAF urges the valve-seat 672 downwards, and into forceful contact with the conical surface 673 of the hammer 670. While the PDAF is below its high-threshold, the PDAF is not yet strong enough to break the magnets apart, nor to dislodge the hammer 670.

    [0054] In Fig.7B, the PDAF has reached the high-threshold, and the magnets 649,652 have broken apart. The valve-seat 672 and the hammer 670 move downwards together, in unison as the movable-unit 647. Then, the downwards motion of the valve-seat 672 is arrested by its striking the shoulder 674 (see Fig.6A) of the fixed component 641. Now, the hammer 670 continues to move downwards on its own.

    [0055] In Fig.7C, the hammer 670 has separated from the valve-seat 672, whereby the pulse-valve 636 is now open. The pulse-valve remains open until the PDAF has fallen to its low-threshold.

    [0056] Figs.8A,8B,8C show the return of the moving components back to the Fig.7A pulse-valve-closed condition. In Fig.8A, the PDAF being now at its low point, the magnets, in attraction, have moved the hammer 670 upwards until a bump 676 on the hammer engages a collet-arm 678 of the movable valve-seat component 672. At this point, the valve-seat 672 is experiencing little resistance to upwards movement, and so the valve-seat 672 is carried upwards by the magnets-induced upwards movement of the hammer 670. The valve-seat 672 travels upwards until its upper face contacts the face 680 of the fixed housing 641, as shown in Fig.8B.

    [0057] Now, the valve-seat 672 can travel upwards no further. But the magnets are capable of moving the hammer 670 upwards, against the resistance of the engagement of the collet-arm 678 with the bump 676. The collet-arm deflects, and allows the bump to pass. The hammer then continues to travel upwards, until the magnets 649,652 are (almost) together, as shown in Fig.8C.

    [0058] Now, even though the pulse-valve 636 is still open at this point, the pulse-valve is almost closed. In fact, the pulse-valve is sufficiently closed for a pressure-drop to develop across the pulse-valve. The PDAF can therefore rise to the (small) magnitude that is all that is needed to drive the valve-seat component 672 downwards, and into forceful contact with the conical surface 673 of the hammer 670. Once the pulse-valve 636 closes, the tool 620 is once more in the condition shown in Fig.7A. The PDAF now rises once more, towards its high-threshold, and a new cycle commences.

    [0059] Figs.9A,9B,9C show another version in which the movable-unit 947 is formed as two separate components, which are movable relative to each other. One movable component is the valve-member 981 itself, and the other component (to which is attached the moving-magnet 949) is a hammer component 983.

    [0060] Fig.9A shows the tool 920 in the pulse-valve-closed condition. The magnets 949,952 are holding the hammer 983 in its uppermost position, against the rising PDAF. The chamber 985 is open to accumulator pressure, which acts downwards against the upper face of the hammer 983 and acts upwards against the downwards-facing annular-area 987 of the movable valve-member 981, thereby urging the valve-member 981 into contact with the valve-seat 940 in the fixed housing 941, and holding the pulse-valve 936 closed. (More accurately, the annular area 987 is the area defined between the diameter of the hammer-seal 989, and the effective diameter of the sealing engagement between the valve-seat 940 and the valve-member 981.)

    [0061] When the PDAF reaches its high-threshold, the hammer 983 moves first, while the valve-member 981 remains still. Fig.9B shows the hammer moving downwards, and about to contact the shoulder 989 of the valve-member 981. Only when the (heavy) hammer 983 has gained some speed and momentum does it then strike the (light) valve-member 981, violently knocking the valve-member clear of the fixed valve-seat 940, and hurling the valve-member 981 to its full-open condition very rapidly indeed. The pulse-valve-open condition is shown in Fig.9C.

    [0062] When the PDAF has fallen to its low-threshold, the magnets 949,952 start the hammer 983 on its upward movement. The ledge 990 on the hammer 983 picks up the valve-member 981, and carries the valve-member to a position in which the pulse-valve 936 is almost closed. At this point, the magnets are (almost) closed together, and the hammer 983 can rise no further. Now, even though the pulse-valve 936 is not quite closed, still a pressure-drop can develop across it, and the resultant PDAF is large enough to drive the valve-member 981 upwards until the valve-member closes against the valve-seat 940, once again, as in Fig.9A.

    [0063] In the above examples, only one pair of magnets is illustrated. However, two, three, four, etc, pairs of magnets can be employed, each pair making its own contribution to the total force available to urge the pulse-valve to its closed position. In a down-hole environment, radial space in the tool is at a premium, but axial (up/down) space is usually of little consequence, and the magnet pairs can be readily incorporated into the tool, one above the other. In respect of each pair, one of the magnets is unitary with the fixed housing, and the other magnet is unitary with the movable-unit. Preferably, the pairs are arranged all in a common oil-bath. Fig.2 shows lower sections 93,94 incorporating extra magnet pairs.

    [0064] The metal components of the tool preferably should be made of stainless steel, not only for the usual down-hole environmental reasons, but because stainless steel, generally, is only mildly magnetic. For most of the components of the tool, the mildly-magnetic e.g type 17-4ph stainless steel is a suitable material.

    [0065] The magnets themselves are shielded by the oil-bath from direct contact with magnetic debris. However, the presence of the magnets can cause the components in which they are housed to become magnetized. This can be advantageous in that the magnetization of the magnet-cups and housing helps to hold the magnets firmly fixed to those components. The outer housing of the tool, at least near the magnets, will be affected by the magnetic forces, and it is likely that particles will adhere to the outer surface of the tool; but it is recognized that this is not troublesome, and that 17-4ph stainless steel is a suitable material.

    [0066] However, the valve-member 38 and the valve-seat 40 are especially vulnerable, since magnetic debris might be very troublesome if these components were to be even slightly magnetized. Therefore, these components preferably should be of metal that is non-magnetic - or preferably, these components should be separated from the magnets by metal that is non-magnetic. (Alternatively, the valve-member 38 and valve-seat 40 can be made of e.g non-magnetic ceramic material.)

    [0067] At the same time, the valve-member and the valve-seat need to be tough and hard-surfaced, since these are the components that move vigorously relative to each other when performing their functions in the tool. Since the highly-non-magnetic stainless steels (e.g type 316 stainless steel) tend not to be the hardest, it is preferred - not to make the valve-member and the valve-seat themselves from non-magnetic material, but - to insulate the valve-member and valve-seat from the magnets by making the intermediate components from non-magnetic material.

    [0068] Thus, in Figs.3-4B, the movable valve-member 38 and the fixed valve-seat 40 are formed as separate components, which can be readily disassembled and replaced, if they do become worn, and these components preferably are made from the hard type 17-4ph (mildly-magnetic) stainless steel. The stem 396 of the movable-unit 47 and the valve section 43 of the housing are made from the type 316 (non-magnetic) stainless steel.

    [0069] The ground formation into which the liquid is being injected is porous and permeable. Pulsing proceeds when the ground conditions are such that the formation pressure rises at a steady rate when the pulse-valve is open, and falls at a steady rate when the pulse-valve is closed. Likewise, the liquid supply and accumulator should be such as to create equivalent steady rates of rise/fall of the accumulator pressure, when the pulse-valve is closed/open.

    [0070] Although they cannot control the rate at which the injected liquid dissipates into the formation, the operators do have control over the high-threshold of the PDAF (at which the pulse-valve opens). The high-threshold can be adjusted by changing the magnetic attraction force (e.g by adding more magnets), or by changing the area of the surfaces that are exposed to the PDAF. Having thus set the high-threshold, of course the operators must see to it also that the supply of liquid is capable of producing an accumulator pressure of the required magnitude. The operators should also provide a suitable flowrate, at that pressure, so that the accumulator recharges itself quickly. The time it takes the accumulator to recharge, after a pulse, is included in the cycle time of the tool.

    [0071] Having set the level of the high-threshold, the operators adjust the level of the low-threshold basically by adjusting the force that is exerted by the magnets (and by the coil-spring, if one is provided) when the pulse-valve is fully open.

    [0072] The rate or frequency at which the pulse-tool creates pulses is thus determined partly by the ground conditions and partly by the adjustments and settings in the tool. However, it should be noted that the pulse-valve opens just as explosively whether the pulse-frequency is fast or slow.

    [0073] In the accompanying drawings, some of the components and assemblies are shown diagrammatically. Of course, the designer must configure the components in such manner that they can be assembled and disassembled.

    [0074] Not all the details of construction are shown in all the drawings. Skilled designers will understand that details from one drawing are, where possible, to be applied also to other drawings, as far as possible. Options shown in connection with one of the drawings should be understood to be optional also in the rest of the drawings, as far as possible.

    [0075] Terms used herein, such as "vertical", "equal", and the like, which define respective theoretical constructs, are intended to be construed according to the purposive construction.

    [0076] A reference to a component being "integral" with another component means, herein, that the two components are either formed from one common piece of material, or, if formed separately, are fixed together in such manner as to be functionally and operationally equivalent to having been formed from one common piece of material.

    [0077] The scope of the patent protection sought herein is defined by the accompanying claims. The apparatuses and procedures shown in the accompanying drawings and described herein are examples.

    [0078] The numerals used in the drawings are summarized as follows.

    Figs.1-2:

    20
    pulse-tool
    21
    surface station
    23
    accumulator
    25
    supply-tubing
    27
    exit-port of pulse-tool
    28
    annular space between tool and casing
    29
    well-casing
    30
    ground formation
    32
    perforations through well-casing
    34
    packer
    36
    pulse-valve
    38
    movable valve-member
    40
    fixed valve-seat
    41
    fixed housing of tool
    43
    valve-section of housing (non-magnetic)
    45
    seat-seal
    47
    movable unit
    49
    moving magnet
    50
    moving magnet-cup
    52
    fixed magnet
    54
    lip of magnet-cup
    93
    additional lower section, containing 2nd pair of magnets
    94
    additional lower section, containing 3rd pair of magnets

    Figs.3-4B:

    320
    pulse-tool
    336
    pulse-valve
    338
    movable valve-member
    340
    fixed valve-seat
    341
    fixed housing of tool
    347
    movable unit
    349
    moving magnet
    352
    fixed magnet
    354
    lips of magnet housings
    356
    oil-bath
    358
    upper oil seal
    360
    lower oil seal
    361
    centre conduit in movable unit 347
    363
    bottom check valve
    365
    top check valve
    367
    nose of housing
    369
    coil spring
    396
    stem of movable unit

    Fig.5

    547
    movable-unit
    558
    upper oil-seal
    560
    lower oil-seal
    562
    pressure-equalizing piston
    564
    bias-spring
    566
    bearings

    Figs.6A-8C

    620
    pulse-tool
    636
    pulse-valve
    641
    fixed housing of tool
    647
    movable unit
    649
    moving magnet
    652
    fixed magnet
    670
    movable hammer
    672
    movable valve-seat
    673
    conical surface
    674
    shoulder in fixed housing
    676
    bump on hammer 670
    678
    collet-arm on hammer
    680
    face in fixed housing

    Figs.9A-9C

    920
    pulse-tool
    936
    pulse-valve
    940
    fixed valve-seat
    941
    fixed housing of tool
    947
    movable unit
    949
    moving magnet
    952
    fixed magnet
    981
    movable valve-member
    983
    movable hammer
    985
    chamber above hammer
    987
    down-facing annular area on valve-member 981
    989
    up-facing shoulder on valve-member 981
    990
    up-facing ledge on hammer 983




    Claims

    1. A downhole tool (20, 320, 620, 920) for pulse-injecting liquid from a borehole out into the surrounding ground-formation, wherein:

    the tool (20, 320, 620, 920) includes a pulse-valve (36, 336, 636, 936);

    the pulse-valve (36, 336, 636, 936) includes a valve-seat and a relatively-movable valve-member;

    the tool (20, 320, 620, 920) includes a pair of magnet-elements (49, 52; 349, 352; 649, 652; 949, 952),

    the magnet-elements are arranged in the tool (20, 320, 620, 920) for magnetic attraction;

    the magnet-elements urge the pulse-valve (36, 336, 636, 936) closed;

    the tool (20, 320, 620, 920) is so configured that the two magnet-elements are close together when the pulse-valve (36, 336, 636, 936) is closed, and apart from each other when the pulse-valve (36, 336, 636, 936) is open;

    whereby, when the pulse-valve (36, 336, 636, 936) opens, the magnetic attraction between the two magnet-elements decreases;

    the tool (20, 320, 620, 920) includes a supply of liquid, stored in an accumulator (23) at accumulator-pressure;

    liquid in the ground formation is at formation-pressure;

    the pressure differential between accumulator-pressure and formation-pressure is termed the PDAF;

    the tool (20, 320, 620, 920) is so configured that, during operation:

    (a) when the pulse-valve (36, 336, 636, 936) is closed, the PDAF is increasing towards a high-threshold at which the pulse-valve (36, 336, 636, 936) opens; and

    (b) when the pulse-valve (36, 336, 636, 936) is open, the PDAF is decreasing towards a low-threshold at which the pulse-valve (36, 336, 636, 936) closes;

    the movable valve-member is a component of a movable-unit, which is movable relative to a fixed housing (41, 341, 641, 941) of the tool (20, 320, 620, 920);

    one of the magnet-elements is integral with the movable-unit, and the other is integral with the fixed housing;

    the tool (20, 320, 620, 920) is so configured that, during operation, the PDAF urges the movable-unit in the direction to open the pulse-valve (36, 336, 636, 936) with a force termed the PDAF-force;

    the PDAF-force is termed the closed-PDAF-force when the pulse-valve (36, 336, 636, 936) is closed;

    the PDAF-force is termed the open-PDAF-force when the pulse-valve (36, 336, 636, 936) is open;

    the magnet-elements bias the valve-member in the direction to close the pulse-valve (36, 336, 636, 936) with a force termed the magnet-force;

    the magnet-force is termed the closed-magnet-force when the pulse-valve (36, 336, 636, 936) is closed;

    the magnet-force is termed the open-magnet-force when the pulse-valve (36, 336, 636, 936) is open;

    the high-threshold of the PDAF is the magnitude of the increasing PDAF at which the closed-PDAF-force equals the closed-magnet-force;

    the low-threshold of the PDAF is the magnitude of the decreasing PDAF at which the open-magnet-force equals the open-PDAF-force;

    whereby the pulse-valve (36, 336, 636, 936) cycles automatically between open and closed.


     
    2. The downhole tool (20, 320, 620, 920) according to claim 1, wherein at least one of the two magnet-elements of the pair is a permanent magnet.
     
    3. The downhole tool (20, 320, 620, 920) according to claim 1, wherein:

    the two magnet-elements are respective permanent magnets;

    each magnet is a rare-earth magnet, of grade N-52 or higher.


     
    4. The downhole tool (20, 320, 620, 920) according to claim 3, wherein each magnet is annular-cylindrical.
     
    5. The downhole tool (20, 320, 620, 920) according to claim 1, wherein:

    a moving-magnet of the pair of magnets is fixedly mounted in the movable-unit;

    the other of the pair of magnets, termed the fixed-magnet, is fixedly mounted in the fixed housing.


     
    6. The downhole tool (20, 320, 620, 920) according to claim 5, wherein:

    the tool (20, 320, 620, 920) includes two or more pairs of magnets, each pair comprising a moving- magnet and a fixed-magnet;

    all the moving-magnets are fixedly mounted in the movable-unit;

    all the fixed-magnets are fixedly mounted in the fixed housing.


     
    7. The downhole tool (20, 320, 620, 920) according to claim 1, wherein:

    the tool includes an oil-bath;

    the oil-bath includes a sealed chamber defined between upper and lower oil-seals, which seal the movable-unit to the fixed housing;

    the two magnet-elements are located inside the sealed chamber, and are immersed in oil therein;

    the tool (20, 320, 620, 920) is so configured that the volume of the enclosed chamber remains constant during movement of the movable-unit relative to the fixed housing.


     
    8. The downhole tool (20, 320, 620, 920) according to claim 1, wherein:

    the movable-unit includes a hammer, and the valve-member is integral with the hammer;

    the one of the magnet-elements that is integral with the movable-unit is integral with the hammer;

    the valve-seat is mounted for movement relative to the fixed-housing;

    the hammer and the valve-seat are formed with respective accumulator-areas, which are exposed to the accumulator pressure, and with respective opposed formation-areas, which are exposed to formation-pressure, the hammer and the valve-seat being thus exposed to the PDAF;

    the tool (20, 320, 620, 920) is so structured that, when the PDAF reaches its high-threshold:

    (a) the valve-seat and the hammer at first move in unison for a small distance, and the magnet-elements separate;

    (b) then the movement of the valve-seat is arrested;

    (b) and the hammer continues to move, and the moving hammer drives the valve- member away from the valve-seat.


     
    9. The downhole tool (20, 320, 620, 920) according to claim 1, wherein:

    the movable-unit includes a hammer;

    the one of the magnet-elements that is integral with the movable-unit is integral with the hammer;

    the hammer and the valve-member are relatively movable;

    the tool (20, 320, 620, 920) is so structured that, when the PDAF reaches its high-threshold:

    (a) the hammer moves in the direction to open the pulse-valve (36, 336, 636, 936), and the magnet-elements separate;

    (b) at first, the valve-member does not move, while the hammer moves a small distance;

    (c) and then, the moving hammer collects the valve-member, and the moving hammer drives the valve-member away from the valve-seat.


     
    10. The downhole tool (20, 320, 620, 920) according to claim 9, wherein the tool (20, 320, 620, 920) is so structured that, when the pulse-valve (36, 336, 636, 936) is closed, the PDAF acts over a small area of the valve-member to bias the valve-member against the valve-seat.
     
    11. The downhole tool (20, 320, 620, 920) according to claim 1, wherein:
    the tool (20, 320, 620, 920) is so structured and arranged that:

    (a) the closed-PDAF-force is substantially larger than the open-PDAF-force, for a given magnitude of the PDAF; or

    (b) the closed-magnet-force is substantially larger than the open-magnet-force; or

    (c) both.


     


    Ansprüche

    1. Tieflochbohrwerkzeug (20, 320, 620, 920) zum Pulseinspritzen von Flüssigkeit aus einem Bohrloch in die umgebende Bodenformation, wobei:

    das Werkzeug (20, 320, 620, 920) ein Pulsventil (36, 336, 636, 936) umfasst;

    das Pulsventil (36, 336, 636, 936) einen Ventilsitz und ein relativ bewegliches Ventilelement enthält;

    das Werkzeug (20, 320, 620, 920) ein Paar Magnetelemente (49, 52; 349, 352; 649, 652; 949, 952) enthält, wobei die Magnetelemente in dem Werkzeug (20, 320, 620, 920) für eine magnetische Anziehung angeordnet sind;

    die Magnetelemente das Pulsventil (36, 336, 636, 936) drängen, geschlossen zu sein;

    das Werkzeug (20, 320, 620, 920) so konfiguriert ist, dass die zwei Magnetelemente nahe aneinander liegen, wenn das Pulsventil (36, 336, 636, 936) geschlossen ist, und voneinander entfernt sind, wenn das Pulsventil (36, 336, 636, 936) offen ist;

    wodurch, wenn das Pulsventil (36, 336, 636, 936) sich öffnet, die magnetische Anziehung zwischen den zwei Magnetelementen abnimmt;

    das Werkzeug (20, 320, 620, 920) eine Flüssigkeitszufuhr enthält, die in einem Akkumulator (23) bei Akkumulatordruck gespeichert ist;

    die Flüssigkeit in der Bodenformation auf Formationsdruck ist;

    die Druckdifferenz zwischen dem Akkumulatordruck und dem Formationsdruck als PDAF bezeichnet wird;

    das Werkzeug (20, 320, 620, 920) so konfiguriert ist, dass, während des Betriebs:

    (a) wenn das Pulsventil (36, 336, 636, 936) geschlossen ist, die PDAF in Richtung eines hohen Schwellenwertes zunimmt, bei dem das Pulsventil (36, 336, 636, 936) sich öffnet; und

    (b) wenn das Pulsventil (36, 336, 636, 936) offen ist, die PDAF in Richtung eines niedrigen Schwellenwertes abnimmt, bei dem das Pulsventil (36, 336, 636, 936) sich schließt;

    das bewegliche Ventilelement eine Komponente einer beweglichen Einheit ist, die relativ zu einem feststehenden Gehäuse (41, 341, 641, 941) des Werkzeugs (20, 320, 620, 920) beweglich ist;

    eines der Magnetelemente einstückig mit der beweglichen Einheit ist und das andere einstückig mit dem feststehenden Gehäuse ist;

    das Werkzeug (20, 320, 620, 920) so konfiguriert ist, dass während des Betriebs die PDAF die bewegliche Einheit in die Richtung drängt, um das Pulsventil (36, 336, 636, 936) mit einer als PDAF-Kraft bezeichneten Kraft zu öffnen;

    die PDAF-Kraft als die geschlossene PDAF-Kraft bezeichnet wird, wenn das Pulsventil (36, 336, 636, 936) geschlossen ist;

    die PDAF-Kraft als die offene PDAF-Kraft bezeichnet wird, wenn das Pulsventil (36, 336, 636, 936) offen ist;

    die Magnetelemente das Ventilelement in die Richtung vorspannen, um das Pulsventil (36, 336, 636, 936) mit einer als die Magnetkraft bezeichneten Kraft zu schließen;

    die Magnetkraft als die geschlossene Magnetkraft bezeichnet wird, wenn das Pulsventil (36, 336, 636, 936) geschlossen ist;

    die Magnetkraft als die offene Magnetkraft bezeichnet wird, wenn das Pulsventil (36, 336, 636, 936) offen ist;

    der hohe Schwellenwert der PDAF die Größe der zunehmenden PDAF ist, bei der die geschlossene PDAF-Kraft der geschlossenen Magnetkraft entspricht;

    der niedrige Schwellenwert der PDAF die Größe der abnehmenden PDAF ist, bei der die offene Magnetkraft der offenen PDAF-Kraft entspricht.

    wodurch das Pulsventil (36, 336, 636, 936) automatisch zwischen offen und geschlossen wechselt.


     
    2. Tieflochbohrwerkzeug (20, 320, 620, 920) nach Anspruch 1, wobei mindestens eines der zwei Magnetelemente des Paars ein Permanentmagnet ist.
     
    3. Tieflochbohrwerkzeug (20, 320, 620, 920) nach Anspruch 1, wobei:

    die zwei Magnetelemente jeweilige Permanentmagnete sind;

    jeder Magnet ein Seltenerdmagnet der Güteklasse N-52 oder höher ist.


     
    4. Tieflochbohrwerkzeug (20, 320, 620, 920) nach Anspruch 3, wobei jeder Magnet ringzylindrisch ist.
     
    5. Tieflochbohrwerkzeug (20, 320, 620, 920) nach Anspruch 1, wobei ein beweglicher Magnet des Magnetpaares feststehend in der beweglichen Einheit angebracht ist;
    wobei der andere Magnet des Magnetpaares, der als feststehender Magnet bezeichnet wird, feststehend in dem feststehenden Gehäuse angebracht ist.
     
    6. Tieflochbohrwerkzeug (20, 320, 620, 920) nach Anspruch 5, wobei:

    das Werkzeug (20, 320, 620, 920) zwei oder mehr Magnetpaare enthält, wobei jedes Paar einen beweglichen und einen feststehenden Magneten umfasst;

    alle beweglichen Magnete feststehend in der beweglichen Einheit angebracht sind;

    alle feststehenden Magnete feststehend in dem feststehenden Gehäuse angebracht sind.


     
    7. Tieflochbohrwerkzeug (20, 320, 620, 920) nach Anspruch 1, wobei:

    das Werkzeug ein Ölbad enthält;

    das Ölbad eine abgedichtete Kammer enthält, die zwischen einer oberen und einer unteren Öldichtung, die die bewegliche Einheit gegen das feststehende Gehäuse abdichten, definiert ist;

    die zwei Magnetelemente sich innerhalb der abgedichteten Kammer befinden und darin in Öl eingetaucht werden;

    das Werkzeug (20, 320, 620, 920) so konfiguriert ist, dass das Volumen der eingeschlossenen Kammer während der Bewegung der beweglichen Einheit relativ zu dem feststehenden Gehäuse konstant bleibt.


     
    8. Tieflochbohrwerkzeug (20, 320, 620, 920) nach Anspruch 1, wobei:

    die bewegliche Einheit einen Hammer enthält und das Ventilelement einstückig mit dem Hammer ist;

    das eine der Magnetelemente, das mit der beweglichen Einheit einstückig ist, mit dem Hammer einstückig ist;

    der Ventilsitz für eine Bewegung relativ zu dem feststehenden Gehäuse angebracht ist;

    der Hammer und der Ventilsitz mit jeweiligen Akkumulatorbereichen, die dem Akkumulatordruck ausgesetzt sind, und mit jeweiligen gegenüberliegenden Formationsbereichen ausgebildet sind, die einem Formationsdruck ausgesetzt sind, wobei der Hammer und der Ventilsitz somit der PDAF ausgesetzt sind;

    das Werkzeug (20, 320, 620, 920) so aufgebaut ist, dass, wenn die PDAF seinen oberen Schwellenwert erreicht:

    (a) der Ventilsitz und der Hammer sich zunächst eine kurze Strecke gemeinsam bewegen, und sich die Magnetelemente trennen;

    (b) die Bewegung des Ventilsitzes dann angehalten wird;

    (b) und der Hammer fortfährt, sich zu bewegen, und der sich bewegende Hammer das Ventilelement von dem Ventilsitz wegbewegt.


     
    9. Tieflochbohrwerkzeug (20, 320, 620, 920) nach Anspruch 1, wobei:

    die bewegliche Einheit einen Hammer enthält;

    das eine der Magnetelemente, das mit der beweglichen Einheit einstückig ist, mit dem Hammer einstückig ist;

    der Hammer und das Ventilelement relativ beweglich sind;

    das Werkzeug (20, 320, 620, 920) so aufgebaut ist, dass, wenn die PDAF seinen oberen Schwellenwert erreicht:

    (a) der Hammer sich in die Richtung bewegt, um das Pulsventil (36, 336, 636, 936) zu öffnen, und sich die Magnetelemente trennen;

    (b) das Ventilelement sich zunächst nicht bewegt, während der Hammer sich eine kleine Strecke bewegt;

    (c) und der sich bewegende Hammer dann das Ventilelement erfasst, und der sich bewegende Hammer das Ventilelement von dem Ventilsitz wegtreibt.


     
    10. Tieflochbohrwerkzeug (20, 320, 620, 920) nach Anspruch 9, wobei das Werkzeug (20, 320, 620, 920) so aufgebaut ist, dass, wenn das Pulsventil (36, 336, 636, 936) geschlossen ist, die PDAF über einen kleinen Bereich des Ventilelements wirkt, um das Ventilelement gegen den Ventilsitz vorzuspannen.
     
    11. Tieflochbohrwerkzeug (20, 320, 620, 920) nach Anspruch 1, wobei:
    das Werkzeug (20, 320, 620, 920) so aufgebaut und angeordnet ist, dass:

    (a) für eine gegebene Größe der PDAF, die geschlossene PDAF-Kraft im Wesentlichen größer als die offene PDAF-Kraft ist; oder

    (b) die geschlossene Magnetkraft im Wesentlichen größer als die offene Magnetkraft ist; oder

    (c) beides.


     


    Revendications

    1. Outil de fond de trou (20, 320, 620, 920) pour l'injection par impulsion, à partir d'un trou de forage, d'un liquide dans la formation souterraine environnante :

    l'outil (20, 320, 620, 920) comprenant une soupape à impulsion (36, 336, 636, 936) ;

    la soupape à impulsion (36, 336, 636, 936) comprenant un siège de soupape et un élément de soupape relativement mobile ;

    l'outil (20, 320, 620, 920) comprenant une paire d'éléments magnétiques (49, 52 ; 349, 352 ; 649, 652 ; 949, 952), les éléments magnétiques étant disposés dans l'outil (20, 320, 620, 920) pour l'attraction magnétique ;

    les éléments magnétiques sollicitant la soupape à impulsion (36, 336, 636, 936) de manière à ce qu'elle se ferme ;

    l'outil (20, 320, 620, 920) étant configuré de telle sorte que les deux éléments magnétiques sont proches l'un de l'autre lorsque la soupape à impulsion (36, 336, 636, 936) est fermée et séparés l'un de l'autre lorsque la soupape à impulsion (36, 336, 636, 936) est ouverte ;

    de sorte que, lorsque la soupape à impulsion (36, 336, 636, 936) s'ouvre, l'attraction magnétique entre les deux éléments magnétiques diminue ;

    l'outil (20, 320, 620, 920) comprenant une réserve de liquide stockée dans un accumulateur (23) sous pression de l'accumulateur ;

    le liquide dans le sol étant sous une pression de formation ;

    la différence de pression entre la pression de l'accumulateur et la pression de formation étant appelée PDAF ;

    l'outil (20, 320, 620, 920) étant configuré de telle sorte que, pendant son fonctionnement :

    (a) lorsque la soupape à impulsion (36, 336, 636, 936) est fermée, la PDAF augmente vers un seuil haut auquel la soupape à impulsion (36, 336, 636, 936) s'ouvre ; et

    (b) lorsque la soupape à impulsion (36, 336, 636, 936) est ouverte, la PDAF décroît vers un seuil bas auquel la soupape à impulsion (36, 336, 636, 936) se ferme ;

    l'élément de soupape mobile étant un composant d'une unité mobile, laquelle est mobile par rapport à un logement fixe (41, 341, 641, 941) de l'outil (20, 320, 620, 920) ;

    l'un des éléments magnétiques étant solidaire de l'unité mobile et l'autre étant solidaire du logement fixe ;

    l'outil (20, 320, 620, 920) étant configuré de telle sorte que, pendant son fonctionnement, la PDAF sollicite l'unité mobile dans la direction d'ouverture de la soupape à impulsion (36, 336, 636, 936) avec une force appelée force PDAF ;

    la force PDAF étant appelée force PDAF fermée lorsque la soupape à impulsion (36, 336, 636, 936) est fermée ;

    la force PDAF étant appelée force PDAF ouverte lorsque la soupape à impulsion (36, 336, 636, 936) est ouverte ;

    les éléments magnétiques sollicitant l'élément de soupape dans la direction de fermeture de la soupape à impulsion (36, 336, 636, 936) avec une force appelée force magnétique ;

    la force magnétique étant appelée force magnétique fermée lorsque la soupape à impulsion (36, 336, 636, 936) est fermée ;

    la force magnétique étant appelée force magnétique ouverte lorsque la soupape à impulsion (36, 336, 636, 936) est ouverte ;

    le seuil haut de la PDAF étant l'intensité de la PDAF croissante à laquelle la force PDAF fermée est égale à la force magnétique fermée ;

    le seuil bas de la PDAF étant l'intensité de la PDAF décroissante à laquelle la force magnétique ouverte est égale à la force PDAF ouverte ;

    de sorte que la soupape à impulsion (36, 336, 636, 936) passe automatiquement entre la position ouverte et la position fermée.


     
    2. Outil de fond de trou (20, 320, 620, 920) selon la revendication 1, dans lequel au moins l'un des deux éléments magnétiques de la paire est un aimant permanent.
     
    3. Outil de fond de trou (20, 320, 620, 920) selon la revendication 1, dans lequel :

    les deux éléments magnétiques sont des aimants permanents respectifs ;

    chaque aimant étant un aimant de terre rare, de catégorie N-52 ou supérieure.


     
    4. Outil de fond de trou (20, 320, 620, 920) selon la revendication 3, dans lequel chaque aimant est cylindrique annulaire.
     
    5. Outil de fond de trou (20, 320, 620, 920) selon la revendication 1, dans lequel :

    un aimant mobile de la paire d'aimants est monté de manière fixe dans l'unité mobile ;

    l'autre aimant de la paire, appelé aimant fixe, est monté de manière fixe dans le logement fixe.


     
    6. Outil de fond de trou (20, 320, 620, 920) selon la revendication 5 :

    l'outil (20, 320, 620, 920) comprenant au moins deux paires d'aimants, chaque paire comprenant un aimant mobile et un aimant fixe ;

    tous les aimants mobiles étant montés de manière fixe dans l'unité mobile ;

    tous les aimants fixes étant montés de manière fixe dans le logement fixe.


     
    7. Outil de fond de trou (20, 320, 620, 920) selon la revendication 1 :

    l'outil comprenant un bain d'huile ;

    le bain d'huile comprenant une chambre étanche définie entre des joints étanches à l'huile supérieur et inférieur, lesquels assurent l'étanchéité entre l'unité mobile et le logement fixe ;

    les deux éléments magnétiques étant situés à l'intérieur de la chambre étanche et immergés dans l'huile s'y trouvant ;

    l'outil (20, 320, 620, 920) étant configuré de telle sorte que le volume de la chambre fermée reste constant pendant le déplacement de l'unité mobile par rapport au logement fixe.


     
    8. Outil de fond de trou (20, 320, 620, 920) selon la revendication 1, dans lequel :

    l'unité mobile comprend un marteau, et l'élément de soupape est solidaire du marteau ;

    l'un des éléments magnétiques solidaires de l'unité mobile est solidaire du marteau ;

    le siège de soupape est monté pour se déplacer par rapport au logement fixe ;

    le marteau et le siège de soupape se composent des zones d'accumulateur respectives exposées à la pression de l'accumulateur, et des zones de formation opposées respectives exposées à une pression de formation, le marteau et le siège de soupape étant ainsi exposés à la PDAF ;

    l'outil (20, 320, 620, 920) étant structuré de telle sorte que, lorsque la PDAF atteint son seuil haut :

    (a) le siège de soupape et le marteau se déplacent, dans un premier temps, à l'unisson sur une petite distance et les éléments magnétiques se séparent ;

    (b) le mouvement du siège de soupape s'arrête ;

    (b) et le marteau reste mobile et le marteau en mouvement éloigne l'élément de soupape du siège de soupape.


     
    9. Outil de fond de trou (20, 320, 620, 920) selon la revendication 1, dans lequel :

    l'unité mobile comprend un marteau ;

    l'un des éléments magnétiques solidaires de l'unité mobile est solidaire du marteau ;

    le marteau et l'élément de soupape sont relativement mobiles ;

    l'outil (20, 320, 620, 920) étant structuré de telle sorte que, lorsque la PDAF atteint son seuil haut :

    (a) le marteau se déplace dans la direction d'ouverture de la soupape à impulsion (36, 336, 636, 936) et les éléments magnétiques se séparent ;

    (b) dans un premier temps, l'élément de soupape reste immobile tandis que le marteau se déplace sur une petite distance ;

    (c) le marteau mobile touche ensuite l'élément de soupape et le marteau mobile éloigne l'élément de soupape du siège de soupape.


     
    10. Outil de fond de trou (20, 320, 620, 920) selon la revendication 9, l'outil (20, 320, 620, 920) étant structuré de telle sorte, lorsque la soupape à impulsion (36, 336, 636, 936) est fermée, la PDAF agit sur une petite zone de l'élément de soupape pour solliciter celui-ci contre le siège de soupape.
     
    11. Outil de fond de trou (20, 320, 620, 920) selon la revendication 1 :
    l'outil (20, 320, 620, 920) étant structuré et disposé de telle sorte que :

    (a) la force PDAF fermée soit sensiblement plus grande que la force PDAF ouverte, pour une intensité donnée de la PDAF ;

    (b) la force magnétique fermée soit sensiblement plus grande que la force magnétique ouverte ; ou de telle sorte que

    (c) les deux cas se produisent.


     




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    Cited references

    REFERENCES CITED IN THE DESCRIPTION



    This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

    Patent documents cited in the description