Device and method for perforation of a downhole formation using acoustic shock waves

Abstract

A device is for perforation of a downhole formation. The device has an electronically induced acoustic shock wave generator; and an acoustic shock wave focusing member. The device is adapted to focus generated acoustic shock waves onto an area of a borehole in order to disintegrate the downhole formation within said area. The device is adapted to generate a plurality of consecutive focused acoustic shock waves in order to gradually excavate a perforation tunnel, or to improve an already existing perforation tunnel, extending from said borehole and into said formation.

Claims

1. A device for perforation of a downhole formation, the device comprising: a single electronically induced acoustic shock wave generator; and an acoustic shock wave focusing member that focuses acoustic shock waves from the single electronically induced acoustic shock wave generator non-divergingly in a propagation direction; wherein the device is adapted to generate a series of acoustic shock waves and to focus the series of acoustic shock waves onto a focus area of a borehole in order to disintegrate the downhole formation within the focus area to gradually excavate a perforation tunnel extending from the borehole and into the downhole formation in the propagation direction of the acoustic shock waves.

2. The device according to claim 1, wherein the acoustic shock wave focusing member is adapted to focus the series of acoustic shock waves in a non-spherical, collimated spatial forward projection onto the focus area.

3. The device according to claim 1, wherein the acoustic shock wave focusing member is adapted to concentrate the series of acoustic shock waves onto the focus area.

4. The device according to claim 1, wherein the device is at least partially covered by a flexible membrane.

5. The device according to claim 1, wherein the electronically induced acoustic shock wave generator is an electrohydraulic acoustic shock wave generator.

6. The device according to claim 1, wherein the series of acoustic shock waves are focused perpendicular to a wall of the borehole.

7. A tool assembly for perforation of a downhole formation, the tool assembly comprising: a first device having a single electronically induced acoustic shock wave generator and an acoustic shock wave focusing member that focuses acoustic shock waves from the single electronically induced acoustic shock wave generator non-divergingly in a propagation direction, wherein the first device is adapted to generate a series of acoustic shock waves and to focus the series of acoustic shock waves onto a focus area of a borehole in order to disintegrate the downhole formation within the focus area to gradually excavate a perforation tunnel extending from the borehole and into the downhole formation in the propagation direction of the acoustic shock waves; wherein the tool assembly is connectable to a wellbore conveying means.

8. The tool assembly according to claim 7, wherein the tool assembly further comprises a casing perforation member.

9. The tool assembly according to claim 7, wherein the tool assembly further comprises a perforation opening localization member.

10. The tool assembly according to claim 7, wherein the tool assembly is adapted to create local underbalanced pressure conditions in the wellbore adjacent the downhole formation being perforated.

11. The tool assembly according to claim 7, wherein the tool assembly further comprises a formation imaging member.

12. The tool assembly according to claim 7, wherein the tool assembly is at least partially covered by a flexible membrane.

13. The tool assembly according to claim 7, wherein the series of acoustic shock waves are focused perpendicular to a wall of the borehole.

14. The tool assembly according to claim 7, further comprising one or more additional devices each having a single electronically induced acoustic shock wave generator and an acoustic shock wave focusing member that focuses acoustic shock waves from the single electronically induced acoustic shock wave generator non-divergingly in a propagation direction, wherein the one or more additional devices are each adapted to generate a series of acoustic shock waves and to also focus the series of acoustic shock waves onto one or more additional focus areas of the borehole in order to disintegrate the downhole formation within the one or more focus areas to gradually excavate one or more perforation tunnels extending from the borehole and into the downhole formation in the propagation direction of the acoustic shock waves, wherein the one or more additional devices are operable concurrently with the first device such that additional perforation tunnels extending from the borehole and into the downhole formation are concurrently excavated in addition to the perforation tunnel excavated via the first device.

15. A method for operating a tool assembly for perforation of a downhole formation, the tool assembly comprising: a device having a single electronically induced acoustic shock wave generator and an acoustic shock wave focusing member that focuses acoustic shock waves from the single electronically induced acoustic shock wave generator non-diveringly in a propagation direction, wherein the device is adapted to generate a series of acoustic shock waves and to focus the series of acoustic shock waves onto a focus area of a borehole in order to disintegrate the downhole formation within the focus area to gradually excavate a perforation tunnel extending from the borehole and into the downhole formation; wherein the tool assembly is connectable to a wellbore conveying means; the method comprising: (A) running the tool assembly into a well on a tool assembly conveying means and positioning the tool assembly adjacent a downhole formation in the well; (B) activating the acoustic shock wave generator; (C) focusing the series of acoustic shock waves generated by the device onto the focus area of the borehole in order to disintegrate the downhole formation within the focus area; and (D) gradually excavating the perforation tunnel via the series of acoustic shock waves in the propagation direction in which the device generates the series of acoustic shock waves.

16. The method according to claim 15, wherein the method, prior to steps (B) (D) further comprises: (Al) creating perforation openings in at least one of a downhole casing or liner via a casing perforation member.

17. The method according to claim 16, wherein the method, prior to steps (B) (D) further comprises: (A2) localizing one or more already existing perforation openings in a casing via a perforation opening localization member.

18. The method according to claim 15, wherein step (D) further comprises: (D1) excavating the perforation tunnel with an axial direction having a vertical component.

19. The method according to claim 15, wherein the method further comprises: (E) maintaining the wellbore at a pressure lower than the formation pressure, at least in the area around the tool assembly when in operation.

20. The method according to claim 15, wherein the series of acoustic shock waves are focused perpendicular to a wall of the borehole.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following is described an example of a preferred embodiment illustrated in the accompanying drawings, wherein:

(2) FIG. 1 shows temporal pressure variation of an acoustic shock wave;

(3) FIG. 2 shows spatial pressure distribution in a focus area of a directed acoustic shock wave field;

(4) FIG. 3 shows spatial pressure distribution in a focus area of a concentrated acoustic shock wave field;

(5) FIG. 4 shows, in a cross-sectional view, a first embodiment of a device according to the first aspect of the invention;

(6) FIG. 5 shows, in a cross-sectional view, a second embodiment of a device according to the first aspect of the invention;

(7) FIG. 6 shows in a cross-sectional view, a third embodiment of a device according to the first aspect of the invention;

(8) FIG. 7 shows in a cross-sectional view, a fourth embodiment of a device according to the first aspect of the invention;

(9) FIG. 8 shows, in a cross-sectional view, a fifth embodiment of a device according to the first aspect of the invention; and

(10) FIG. 9 shows a tool assembly according to the second aspect of present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

(11) In the following, the reference numeral 1 will indicate a device according to the first aspect of present invention, whereas the reference numeral 10 will indicate a tool assembly according to the second aspect of the invention, the tool assembly 10 comprising one or more devices 1 according to the first aspect of the invention. The drawings are shown schematically and simplified and the various features in the drawings are not necessarily drawn to scale.

(12) A shock wave field is a spatial and temporal distribution of acoustic energy within a three-dimensional space. In FIG. 1, an example of a temporal pressure variation of a typical acoustic shock wave is shown. The impact that such an acoustic shock wave will have on a downhole formation depends both on the energy contained in the acoustic shock waves as well as its confinement in time and space. The actual power density required to disintegrate the formation will vary greatly between different types of downhole formations.

(13) In FIG. 2 the pressure distribution near the focus area of a substantially ideal directed/collimated acoustic shock wave is shown. The pressure within the focus area F is substantially uniform in the direction normal to the propagation of the acoustic wave. In use in a device 1 according to the first aspect of the invention, the power density in the focus area will be optimized so as to be sufficient to disintegrate the formation area onto which the acoustic shock wave is directed. It will thereby, by generating a series of consecutive focused acoustic shock waves, be possible to gradually excavate a perforation tunnel into the formation. The devices 1 shown in FIGS. 4 and 8, discussed below, are adapted to generate a pressure distribution similar to the one shown in FIG. 2.

(14) In contrast, FIG. 3 shows the corresponding pressure distribution for a concentrated acoustic shock wave with a focus area F and a focal point P+ at its peak. Such a pressure distribution will be obtainable by means of the devices shown in FIGS. 5-7, discussed below. The focus area F is still described as the area, normal to the direction of propagation, in which the shock wave has sufficient power density to disintegrate the formation.

(15) FIG. 4 shows a first embodiment of a device 1 according to the first aspect of present invention. An acoustic shock wave generator, here in the form of an electrohydraulic generator 2a, is placed within an acoustic shock wave focusing member 4a in the form of a parabolically shaped reflector. The parabolic reflector 4a spreads acoustic shock waves S from the electrohydraulic generator 2a and focuses the acoustic shock waves S in a collimated spatial forward projection onto a focus area F on a borehole 44 of a wellbore. The acoustic wave front includes a combination of a directed, focused part of the waves, and a weaker, unfocused/diverging part of the wave. A flexible membrane 5 is provided across the opening of the parabolic reflector 4a in order to maintain the electrohydraulic generator 2a in a controlled, liquid-filled environment to ensure control and reproducibility of the energy characteristics of the electrohydraulic generator 2a. The flexibility of the membrane 5 may ensure smooth transfer of acoustic energy past the membrane 5 without substantial absorption of energy therein.

(16) FIG. 5 shows a second embodiment of a device 1 according to the first aspect of the present invention. An acoustic shock wave generator, here in the form of an electrohydraulic generator 2a, is placed within an acoustic shock wave focusing member 4b in the form of an elliptically shaped reflector that concentrates, rather than collimates, generated acoustic shock waves S onto a focus area F of a borehole 44 in a wellbore. The main part of the wave front is converging towards the focus area F, while a weaker part of the wavefront is diverging. The opening in the elliptically shaped reflector 4b is covered by a flexible membrane 5 for similar reasons as discussed above.

(17) FIG. 6 shows a third embodiment of a device 1 according to the first aspect of the invention. In the figure an acoustic shock wave generator, here in the form of a cylindrical electromagnetic generator 2b, is placed within an acoustic shock wave focusing member 4c in the form of a parabolically shaped reflector. Generated acoustic shock waves S are focused onto an area F on the borehole 44 in a converging wavefront. The electromagnetic generator 2b could also have been provided as a piezoelectric generator in an alternative embodiment.

(18) FIG. 7 shows a fourth embodiment of a device 1 according to the first aspect of the invention. An acoustic shock wave generator, here in the form of a substantially circular, flat piezoelectric generator 2c, is shown generating acoustic shock waves S that propagate towards an acoustic shock wave focusing member in the form of a concentrating acoustic lens 4d that concentrates and projects the acoustic shock waves S onto an area projection F on the borehole 44 of a wellbore in a converging wavefront. In an alternative embodiment, the shown circular, flat generator could also be electromagnetic. In another embodiment, a plurality of circular and flat piezoelectric or electromagnetic generators may be provided in a stacked arrangement.

(19) FIG. 8 shows a fifth embodiment of a device 1 according to the first aspect of the invention. An acoustic shock wave generator, here in the form of a substantially circular, flat piezoelectric generator 2c, is shown generating acoustic shock waves S that propagate towards an acoustic shock wave focusing member in the form of an acoustic horn 4e, resulting in a collimated wavefront onto the focus area F on the borehole 44. The acoustic horn 4e, which is interchangeably referred to as an ultrasonic horn, is typically formed in a piece of metal, such as titan, and fixedly connected, by means of gluing, welding, bolts etc., to the generator 2c. In an alternative embodiment, the shown circular, flat generator could also be electromagnetic. In another embodiment, a plurality of circular and flat piezoelectric or electromagnetic generators may be provided in a stacked arrangement.

(20) FIG. 9 illustrates a tool assembly 10 according to the second aspect of the present invention comprising a plurality of acoustic shock wave devices 1 according to the first aspect of the invention. The tool assembly being deployed into a well 12 on a wellbore conveying means in the form a wireline 14. The well 12 is completed by means of a wellhead 16 at the surface. Below the wellhead 16 an outer casing 18 extends into the well 12, the outer casing 18 constituting a radial delimitation between a portion of a wellbore 20 of the well 12 and a downhole formation 22. A layer of cement 24 is provided in the annulus between the outer casing 18 and the formation 22 in order to keep the outer casing firmly in place and to prevent unwanted leaks from the formation 22 and into the annulus between the outer casing 18 and the formation 22. An open bottom tubing 26, shorter than the outer casing 18 and with a smaller diameter than the outer casing 18, is shown extending from the wellhead 16 and down into the wellbore 20 substantially concentrically inside the outer casing 18.

(21) Below the outer casing 18, the wellbore 20 extends further into the formation as an open-hole configuration section 21. In the shown embodiment, the upper portion of the formation 22 includes an area of cap rock 28, while a lower portion of the formation includes permeable zones 30, 32, 34. In the shown embodiment perforations 36 have already be formed in the formation 22 in the upper permeable zone 30. The perforations 36 include perforation openings 38 formed in the outer casing 18 and continuous perforation tunnels 40 extending from the perforation openings 38, through the cement 24 and in to the upper permeable zone 30. A mid permeable zone 32 exists below the upper permeable zone 30, outside a lower portion of the outer casing 18, whereas a lower permeable zone exists adjacent the wellbore in the open-hole section 21. A mid non-permeable zone 31 separates the upper permeable zone 30 and mid permeable zone 32, while a lower non-permeable zone 33 separates the mid permeable zone 32 and the lower permeable zone 34. The perforations 36 have been formed using not shown shaped explosive charges. The tool assembly 10 is connected to the wireline 14 at a cable head 42 of the tool assembly 10. The wireline 14 is adapted to transmit low/high power electricity and/or laser energy from a not shown power generator and/or laser generator at the surface to a laser cutting tool 35. In the shown embodiment, the tool assembly further comprises a formation imaging members 37, particularly useful for monitoring the excavation and quality of the perforations 36. The formation imaging member 37 may be of any type mentioned herein. Further, the tool assembly comprises pair of inflatable packers 39 adapted to create isolate a portion of the wellbore 20 if needed. The inflatable packers may e.g. be used for creating local underbalanced conditions in the wellbore 20 in the part of the formation 22 being perforated. The tool assembly 10 further comprises a perforation opening localization member 41, which may be of any type mentioned herein. The tool assembly 10 in the shown embodiment is adapted to convert, store/accumulate and discharge power received from the surface by means of an acoustic shock wave sub 43, the acoustic shock wave sub 43 typically including a transformer, capacitors or other accumulators, and a discharge unit in order to power the plurality of acoustic shock wave devices 1 according to the first aspect of the invention when needed. The activation may be automatically triggered or by means of command from the surface. It should be noted that the different features of the tool assembly 10 may be provided in different arrangements and orders, and that the tool assembly 10 according to the second aspect of the invention, in the widest sense, is defined by the claims.

(22) Hereinafter different possible methods of operations, as also mentioned previously herein, will be briefly explained. In a first mode of operation, the tool assembly 10 may be lowered down to the lower permeable zone 34 in the open-hole section 21 of the wellbore 20. After positioning the tool assembly adjacent the lower permeable zone 34, the plurality of acoustic shock wave devices 1 according to the first aspect of the invention may be activated so as to focus a plurality of acoustic shock waves onto the borehole 44 of the un-cased wellbore 20. The part of the tool assembly 10 comprising the plurality of acoustic shock wave devices 1 according to the first aspect of the invention is covered by a flexible membrane 5. The focused acoustic shock waves may be of the concentrated or directed types described above. The overall idea is that the focused projection F, as shown in FIGS. 4-8, of the acoustic shock waves onto the borehole 44 has a sufficiently high acoustic power density to disintegrate the formation 22 within the focused area. By repeating the generation process a substantial number of times, perforation holes will form in the borehole 44 extending into not shown perforation tunnels in the lower permeable zone 34 by gradual excavation thereof. If a series of concentrated acoustic shock waves is used, the focus area will typically remain at the perforation opening, where the borehole 44 has been perforated, also when excavating the perforation tunnel, then by way of a water-hammer effect as mentioned previously herein. If a directed acoustic shock wave is used, the focus will remain directed into the axial direction of the gradually excavated perforation tunnel. As mentioned above, the perforation tunnel may be formed with a vertical component along the axial direction thereof, typically by slightly lowering the tool assembly after first having excavated shallow holes in the borehole 44, following the steps as mentioned above. Then directing slightly upwardly, automatically or controlled from the surface, the acoustic shock wave devices 1 with their acoustic shock wave focusing members, by way of not shown mechanical means individually coupled to each device, aligning the devices' focus areas within the shallow holes just generated, re-activating the plurality of acoustic shock wave devices 1 to gradually excavate not shown perforation tunnels into the lower permeable zone 34, now with a vertical component along the axial direction thereof, thus simplifying the removal of debris from the perforation tunnel and into the wellbore 20. By generating acoustic shock waves resulting in power densities just above the required formation degeneration densities perforations may be made that do not comprise the virgin permeability of the lower permeable zone 34, nor other parts of the wellbore 20, and therefore increases the overall productivity/injectivity of the well 12. In one embodiment, the steps in the mentioned first mode of operation may be used in combination with, or as a pre-step to, running a not shown downhole wireline formation tester, such as a MDT (modular formation dynamics tester) tool or similar, for the purpose of enhancing the coupling between the probe(s) of the wireline formation tester and the borehole 44, as well as the communication between the borehole 44 and a more virgin (not shown, lesser drilling mud contaminated) formation, for improved measurement/sampling quality.

(23) In a second mode of operation, the tool assembly 10 may be lowered down to the mid-permeable zone 32. The mid-permeable zone 32 is delimitated from wellbore 22 by means of the outer casing 18 and cement 24 as described above. The acoustic shock wave devices 1 are, in the shown embodiment, not adapted to make perforation openings through the casing 18. Instead the tool assembly is provided with high power laser cutting tool 35 for making not shown perforation openings in the outer casing 18. References to relevant prior art documents disclosing examples of such laser cutting tools 35 were given above. Perforation openings in the outer casing 18 may also be formed using other casing perforation members as previously discussed, or the perforation openings may be pre-formed in the outer casing 18 and activatable by means of not shown sliding or rotation casing sleeves. After perforation openings have been formed, the plurality of acoustic shock wave devices 1 as included in the tool assembly 10 are directed with their acoustic shock wave focusing members toward the perforation openings formed in the outer casing 18, so as to gradually excavate not shown continuous perforation tunnels through the cement 24 and into the permeable zone 32.

(24) In a third mode of operation, the tool assembly 10 may be lowered to the upper permeable zone 30. In this embodiment, a plurality of perforations 36 have already been formed using not shown shaped explosive charges. The perforations 36 may have been formed during the same run, or during an earlier run into well 12. The tool assembly 10 is adapted to locate the perforation openings 38 in the outer casing 18, by means of the perforation opening localization member 41, and to align the plurality acoustic shock wave devices 1 with the openings perforation openings 38. The acoustic shock wave devices will subsequently be activated to generate a series of consecutive focused acoustic shock waves in order to gradually, and gently improve the perforation tunnels 40, improving typically implying widening and/or extending.

(25) The different modes of operation discussed above may be used in one and the same well or in different wells. The different zones shown in FIG. 9 and discussed above may therefore also be construed as representing different wells.

(26) It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb comprise and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article a or an preceding an element does not exclude the presence of a plurality of such elements.

(27) The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.