EP0322347B1 - Trépan racleur avec buses pour le forage de formations plastiques - Google Patents

Trépan racleur avec buses pour le forage de formations plastiques Download PDF

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Publication number
EP0322347B1
EP0322347B1 EP88710035A EP88710035A EP0322347B1 EP 0322347 B1 EP0322347 B1 EP 0322347B1 EP 88710035 A EP88710035 A EP 88710035A EP 88710035 A EP88710035 A EP 88710035A EP 0322347 B1 EP0322347 B1 EP 0322347B1
Authority
EP
European Patent Office
Prior art keywords
bit
cutting surface
blade
drag bit
drag
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
EP88710035A
Other languages
German (de)
English (en)
Other versions
EP0322347A1 (fr
Inventor
Gordon A. Tibbits
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Baker Hughes Oilfield Operations LLC
Original Assignee
Eastman Teleco Co
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Eastman Teleco Co filed Critical Eastman Teleco Co
Publication of EP0322347A1 publication Critical patent/EP0322347A1/fr
Application granted granted Critical
Publication of EP0322347B1 publication Critical patent/EP0322347B1/fr
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • E—FIXED CONSTRUCTIONS
    • E21—EARTH OR ROCK DRILLING; MINING
    • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B10/00—Drill bits
    • E21B10/60—Drill bits characterised by conduits or nozzles for drilling fluids
    • E21B10/602—Drill bits characterised by conduits or nozzles for drilling fluids the bit being a rotary drag type bit with blades
    • E—FIXED CONSTRUCTIONS
    • E21—EARTH OR ROCK DRILLING; MINING
    • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B10/00—Drill bits
    • E21B10/46—Drill bits characterised by wear resisting parts, e.g. diamond inserts
    • E21B10/56—Button-type inserts
    • E21B10/567—Button-type inserts with preformed cutting elements mounted on a distinct support, e.g. polycrystalline inserts
    • E21B10/5671—Button-type inserts with preformed cutting elements mounted on a distinct support, e.g. polycrystalline inserts with chip breaking arrangements
    • E—FIXED CONSTRUCTIONS
    • E21—EARTH OR ROCK DRILLING; MINING
    • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B10/00—Drill bits
    • E21B10/46—Drill bits characterised by wear resisting parts, e.g. diamond inserts
    • E21B10/56—Button-type inserts
    • E21B10/567—Button-type inserts with preformed cutting elements mounted on a distinct support, e.g. polycrystalline inserts
    • E21B10/5673—Button-type inserts with preformed cutting elements mounted on a distinct support, e.g. polycrystalline inserts having a non planar or non circular cutting face

Definitions

  • the invention relates to a drag bit for drilling a borehole in an earth formation as set forth in the pre-characterizing portion of claim 1.
  • Drilling in shales or plastic formations with a drag bit has always been difficult.
  • the shale, under pressure and in contact with hydraulics, tends to act like a sticky bubble-gum-like mass, sometimes referred to as gumbo, which balls and clogs the bit. Once the bit balls up, it ceases to cut effectively.
  • GB-A-2 181 173 shows a bladed drag bit of the type referred to with a plurality of cutters on each blade in combination with a nozzle which creates a vortex flow having a peripheral stream extending across the cutting elements and exiting into a gage region.
  • a proportion of the drilling fluid is allowed to escape from the central portion of the vortex through a circular exit passage extending azimuthally through the blade of the bit to open into an exit channel in the gage region.
  • the cutters are spaced cutters and the nozzle is azimuthally disposed in front of the blade. This does not provide for a directed hydraulic impingement on the chips effectively preventing balling up the bit when drilling in plastic formations.
  • EP-A-233 737 shows a bladed drag bit of a similar construction including discharge nozzles arranged in front of the blades and directing fluid against the formation in advance of the cutting elements. Such a direction of fluid tends to remove cuttings from the formation prior to the cutting action of the cutting elements, but does not effectively prevent adhesion of chips to the cutting surface.
  • the invention is a drag bit comprising the features of claim 1.
  • the invention is further a method of preventing bit balling as claimed in claim 14. Further embodiments of the drag bit are characterized in claims 2-13 and of the method in claims 15-18.
  • Figure 1 is a perspective view of a completed drag bit incorporating the invention.
  • Figure 2 is a diagrammatic plot sketch of the drill bit illustrated in Figure 1.
  • Figure 3 is a diagrammatic profile of one of the cutting blades of the bit illustrated in Figures 1 and 2.
  • Figure 4 is a highly diagrammatic partial cross-sectional view in enlarged scale illustrating the cutting and hydraulic action of one blade of the invention.
  • Figure 5 is a perspective illustration of an alternative embodiment of the bit using half-round diamond cutters in the blade.
  • Figure 6 is a perspective view in enlarged scale of one of the cutting slugs in the bit of Figure 5 shown in isolation of the bit.
  • Figure 7 is a side view of the cutter slug of Figure 6.
  • Figure 8 is a perspective illustration of another embodiment of the invention where the cutting slugs are provided with rectangular diamond faces.
  • Figure 10 is a perspective illustration of yet another embodiment of the invention wherein triangular diamond faces are combined on the blade of a bit made according to the invention.
  • a drag bit having a cutting face formed of a plurality of generally radially extending open arched blades.
  • Each arched blade is provided with a cutting face and defines a cavity beneath the arch to the bit body.
  • the cutting elements on the arched blade may include a plurality of synthetic polycrystalline diamonds which are cut, sized and shaped to conformally fit with each other so as to present a substantially diamond-only surface as a cutting surface of the bit.
  • Hydraulic nozzles are defined in the bit body beneath and azimuthally behind the arches formed by each blade. The nozzles direct hydraulic flow across the cavity under the arch and across each portion of the cutting face on the arch.
  • FIG 1 is a perspective illustration of a completed drag bit of the preferred embodiment fabricated through molding according to the invention using conventional metal matrix infiltration methodology.
  • Drag bit 10 is characterized by a threaded portion 12 on the upper end of the shank (inverted in Figure 1 for ease of visualization). Threaded portion 12 is integral with shank 14 and shank 14 is integral with bit body 16.
  • Bit body 16 is comprised of gage 18 and, in the illustrated embodiment, three blades 20. The number of blades is not material to the invention.
  • each blade 20 is a plurality of synthetic polycrystalline diamond slug cutters 22 formed on the top of the arch comprised by blade 20. Cutters 22 extend from the center of bit 10 to its gage 18. Each blade forms a web characterized by an open cavity 24. Between blades 20 is an open space which forms a large open waterway 26 and face junk slot 28. The demarcation between waterway 26 and face junk slot 28 is somewhat arbitrary, but face junk slot 28 is generally the region adjacent the face 30 of bit body 16 and proximate the lower portion of waterway 26.
  • Face junk slot 28 communicates with upper junk slot 32 which in turn extends to the upper part of the gage (again Figure 1 being inverted for ease of visualization, necessarily has upper junk slot 32 depicted below face junk slot 28 and waterway 26 in the depiction of Figure 1).
  • Gages 18 also includes a plurality of longitudinal broaches 34 and ribs bearing gage diamond kickers 36. Kickers 36 are typically comprised of embedded natural diamonds or fragments of worn synthetic diamonds.
  • each cavity 24 In the bottom of each cavity 24 are one or more nozzles 38 which direct hydraulic fluid from behind and upwardly across the face of cutters 22.
  • the position of nozzles 38, cutters 22, blades 20 and waterways 26 can be better understood and visualized by now turning to the plot sketch of Figure 2.
  • the plot sketch is a diagrammatic plan view of bit 10 of Figure 1.
  • cutters 22 are compax cutters which typically are comprised of a polycrystalline synthetic diamond table 40, mounted, bonded or otherwise fixed to a metallic backing slug 42 which in turn is set within a cutter body 44 manufactured as part of the infiltration molding process. It is to be expressly understood that many other types of cutting elements or diamond cutters, e.g.
  • each diamond table 40 is in the shape of a generally circular disc approximately one inch or more in diameter. It is also contemplated that fractions of a circular cutter may be used, such as half circular cutting elements. As will be described below, many other types, shapes and sizes of cutters may be employed according to the invention without departing from its scope.
  • each of the primary cutters 22 overlaps with at least one adjacent cutter.
  • a series of cutters 22 forms a three-dimensional arch as depicted in Figure 1, and as more simply and graphically depicted in the profile sketch of one of blades 20 in Figure 3.
  • a first cutter denoted by reference numeral 22a as shown in Figure 3, is disposed near the apex portion of blade 20. It is a full circle.
  • the next adjacent cutter 22b has been moon-cut so that it fits cutter 22a in a complementary manner and so that diamond tables 40 of cutters 22a and 22b are seen and act as a single diamond-only face. It should be noted that little or no matrix metal of bit 10 is presented to the rock formation in the proximity of the cutting blade.
  • the next two adjacent cutters also denoted by reference numeral 22b, have the same complementary fit as cutter 22b which is adjacent to cutter 22a. Cutters 22c are also moon-cut to provide a complimentary fit.
  • gage cutter 54 there are four cutters 22c which complete the diamond arch on web 20.
  • the radial outermost cutter 22c extends radially from the longitudinal center of bit 10 to the gage diameter.
  • Further gage definition is provided by a smaller diamond slug cutter 54 placed above the radial outermost cutter 22c which depicted below cutter 22c in Figure 3.
  • gage cutter 54 is rotated azimuthally outward or side raked.
  • Additional gage definition and protection are provided by similar small slug cutters 56 which are azimuthally displaced behind the arch of primary cutters 22a-22c again as best depicted in Figure 2.
  • Figure 3 shows that such supplementary cutters 56 longitudinally overlap the radial outermost cutter 22c and its corresponding gage cutter 54.
  • the cutter placement as just described is repeated three times in the bit, once for each blade 20, thereby providing a triple redundancy of cutters and cutting action.
  • the degree of redundancy could of course be increased or decreased according to the number of blades used.
  • Blade 20 is particularly characterized as depicted in Figure 3 as forming an open web characterized by a cavity 24 which underlies the arch of primary cutters 22a-22c. As shown in Figure 1, cavity 24 is completely open allowing free communication through each blade. However, disposed in the bottom of each blade is one or more nozzles 38 which are best depicted in Figure 2. Nozzles 38 are placed in the base portion 58 of the web best seen in Figure 3 which defines cavity 24 and behind the arch formed by cutters 22a-22c. In the illustrated embodiment, two sets of nozzles are provided for each blade 20.
  • Nozzle 38a for example, provides a directed flow as symbolically denoted by arrow 60 which fans out from behind, down and then across the diamond tables 40 of cutters 22b-22c from approximately the midpoint to the gage end of the arch of cutters.
  • Nozzle 38b similarly provides a directed flow, as symbolically denoted by arrow 62, across cutters 22a-22b from the midpoint to the apex of the arch of cutters.
  • the hydraulic flow and its coaction with chip removal is best depicted in connection with Figure 4.
  • Figure 4 is a diagrammatic cross-sectional view taken through cavity 24 of one of blades 20 as the bit is cutting into a formation 64.
  • the primary cone of hydraulic flow is symbolically depicted as cone 66.
  • the flow is ejected by nozzle 38 through cavity 24 downwardly and from behind cutters 22a. Chips being gouged from formation 64 are extruded upwardly across the face of diamond table 40 of cutter 22 and caught at their upper edge by the hydraulic flow contained within and adjacent to cone 66.
  • the hydraulic flow peels chip 68 away from the face of diamond table 40.
  • chip 68 becomes of such a size that it separates from formation 64 and is transported by the hydraulic flow into waterways 26, face junk slots 38 and junk slots 32.
  • chips are entrained in the hydraulic flow up the borehole and carried to the well surface.
  • chip 68 only contacts the cutting faces of diamond tables 40 and no other portion of the bit is presented for impact or diving contact with chips 68.
  • chips 68 are exposed and impacted by hydraulic flow 66 from behind cutters 22. Cavities 24 are believed to act as chip breakers and to allow large chips 68 to be broken into smaller, more manageable pieces at the bit crown.
  • the open design of bit 10 also allows a great deal of chip dynamics and turbulence to be created at the bit crown at the expense of a very limited amount of hydraulic volume.
  • bit 10 is able to operate at lower hydraulic volumes and pressures and to tolerate a degree of plasticity in formations that would not otherwise be possible with cutter designs allowed or permitted greater impact between chips 68 and noncutting surfaces of bit 10. Chips 68, almost regardless of their plasticity or stickiness, have very little opportunity to contact or adhere to any surface of the bit before being broken up, pressure relieved, hydrated and carried away.
  • bit 10 is manufactured using conventional metal matrix infiltration techniques.
  • a metal blank body serves as the core of the bit, to which the blades are attached and around which the metal matrix is infiltrated.
  • the blank has a generally cylindrical form comprised of a base portion which is machined at its lower end.
  • bit blank once assembled, is inserted into a conventional graphite mold (not shown) together with a number of additional carbon and sand pieces which will define cavity 24, waterways 26, face junk slot 28 and junk slot 32 among other details of the bit face. Cutters 22 will be milled or defined into the bottom of the graphite mold, and the bit blank, as described with its various carbon pieces, is aligned within the bit mold relative to the cutter blanks and other bit face features set up within the mold.
  • dummy blanks will be placed within the mold in place of the cutting slugs and the diamond tables. After the bit is fabricated, the dummy slugs will be removed and the diamond compax slugs may then be brazed or otherwise secured to the bit at a lower temperature than the infiltration temperature, which lower temperature will not degrade the diamond.
  • the diamond cutters may be directly furnaced into the bit as the metal matrix is infiltrated around the bit blank.
  • FIG. 5 a bit, generally denoted by reference numeral 200, is depicted wherein a plurality of semicircular diamond tables 210, which are comprised of slug cutters 202 which are made from cutters of the first embodiment which have been cut in half, are used to form the cutting elements in the blade arch.
  • This allows relative inversion of the cutters along the gage of bit 200, as exemplified by cutter 204 as compared to cutters 210 to enhance gage definition.
  • cutter 202 could be formed on tungsten carbide slugs 206 carrying a tungsten carbide backing 208 behind diamond table 210.
  • a side view of slug 206 is depicted in Figure 7 and a perspective view is shown in Figure 6.
  • FIGS 8 and 9 Yet another embodiment is shown in Figures 8 and 9 wherein rectangular diamond tables are laser cut from large cylindrical discs to provide a diamond cutting bar 302 of bit 300.
  • diamond plates 304 are covered with diamond plates 304 in a mosaic or tile pattern as best depicted in the cross-sectional view shown in Figure 9 of one of the blades depicted in Figure 8.
  • FIG. 10 Yet another embodiment may be devised as shown in the perspective view of figure 10 wherein the diamond tables of the slug cutters are formed or cut into a triangular shape to comprise cutters 402 of bit 400. Again, the only surface of the blade which is substantially exposed as a cutting surface is a diamond-only surface and no opportunity is provided to the plastic chips to adhere to any other surface of the bit.

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  • Engineering & Computer Science (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Mining & Mineral Resources (AREA)
  • Geology (AREA)
  • Mechanical Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Environmental & Geological Engineering (AREA)
  • Fluid Mechanics (AREA)
  • General Life Sciences & Earth Sciences (AREA)
  • Geochemistry & Mineralogy (AREA)
  • Chemical & Material Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Earth Drilling (AREA)

Claims (18)

  1. Trépan à lames (10) pour le forage d'un trou dans un sol (64) comprenant un corps de trépan (16) traversé de part en part par un passage de fluide, au moins une lame (20) s'étendant dans l'ensemble radialement et présentant un premier côté d'attaque et un second côté de fuite par rapport au sens de rotation prévu pour le trépan (10), lors du forage, ladite au moins une lame (20) s'étendant longitudinalement à partir du corps de trépan (16) et étant fixée à celui-ci, une surface de coupe (40, 210, 302) sur le premier côté de ladite au moins une lame (20), à proximité d'une cavité à extension azimutale (24) associée à la lame (20) et au moins un ajutage (38) associé à ladite au moins une lame (20) et communiquant avec le passage de fluide du corps de trépan (16), caractérisé en ce que ledit au moins un ajutage (38) est disposé et orienté de manière à diriger un flux de fluide à proximité de la surface de coupe (40, 210, 302) depuis l'arrière de la surface de coupe (40, 210, 302) et généralement dans le sens de rotation du trépan.
  2. Trépan à lames suivant la revendication 1, dans lequel la cavité (24) s'étend dans l'ensemble radialement entre le corps de trépan (16) et la surface de coupe (40, 210, 302).
  3. Trépan à lames suivant la revendication 2, dans lequel ledit au moins un ajutage (38) est disposé au moins partiellement à l'intérieur de la cavité (24).
  4. Trépan à lames suivant les revendications 1, à 3, dans lequel ledit au moins un ajutage (38) est orienté dans le sens général de rotation du trépan.
  5. Trépan à lames suivant l'une quelconque des revendications 1 à 4, dans lequel ledit au moins un ajutage (38) comprend au moins deux ajutages (38), chaque ajutage (38) étant orienté de manière à diriger un flux de fluide à partir du passage de fluide à proximité d'une partie latérale différente de la surface de coupe (40, 210, 302).
  6. Trépan à lames suivant la revendication 1, dans lequel ladite au moins une lame (20) s'étend radialement de manière à définir le calibre du trou foré.
  7. Trépan à lames suivant la revendication 1, dans lequel la surface de coupe (40, 210, 302) est sensiblement continue.
  8. Trépan à lames suivant la revendication 7, dans lequel la surface de coupe (40, 210, 302) comprend une pluralité d'éléments de coupe (22, 202), des éléments de coupe sélectionnés (22, 202) de la pluralité d'éléments de coupe (22, 202) étant taillés de manière conforme afin d'engager latéralement et d'abouter des éléments de coupe adjacents (22, 202).
  9. Trépan à lames suivant la revendication 1, dans lequel la surface de coupe (40, 210, 302) comprend une surface de coupe en substance exclusivement en diamant (40, 210, 302).
  10. Trépan à lames suivant la revendication 1, dans lequel ladite au moins une lame (20) comprend une pluralité de lames (20) qui s'étendent dans l'ensemble radialement.
  11. Trépan à lames suivant la revendication 10, dans lequel les lames (20) de la pluralité présentent chacune une première extrémité radialement externe et une seconde extrémité radialement interne, la première extrémité de chaque lame (20) étant fixée de manière indépendante au corps de trépan (16) et sa seconde extrémité étant fixée en commun avec les secondes extrémités des autres lames (20) au corps de trépan (16).
  12. Trépan à lames suivant la revendication 10, dans lequel chacune des lames (20) contient une cavité (24) qui s'étend entre le premier et le second côté de la lame pour former un espace toroïdal continu entre le corps de trépan (16) et la surface de coupe (40, 210, 302).
  13. Trépan à lames suivant les revendications 4 et 10, dans lequel ledit au moins un ajutage (38) est disposé derrière le second côté de la lame et est orienté dans le sens général de rotation du trépan de manière à diriger un flux de fluide à proximité de la surface de coupe (40, 210, 302) à travers la cavité (24).
  14. Procédé pour empêcher le bourrage du trépan lors de la taille d'une formation rocheuse plastique (64) à l'aide d'un trépan à lames (10), comprenant les étapes consistant à fournir un trépan à lames (10) comportant un corps de trépan (16) et une surface de coupe (40, 210, 302), à faire tourner le trépan à lames (10), à ne présenter en substance que la surface de coupe (40, 210, 302) à la formation rocheuse plastique (64), à tailler la formation rocheuse plastique (64), à l'aide de la surface de coupe (40, 210, 302) et à évacuer les débris de roche (68) taillés par la surface de coupe (40, 210, 302) par un flux hydraulique dirigé, caractérisé en ce qu'on dirige le flux hydraulique depuis l'arrière de la surface de coupe (40, 210, 302) et d'une manière générale dans le sens de rotation du trépan.
  15. Procédé suivant la revendication 14, dans lequel le flux est dirigé principalement vers la partie de la surface de coupe (40, 210, 302) la plus éloignée de la formation plastique (64).
  16. Procédé suivant la revendication 14, dans lequel l'étape consistant à évacuer les débris de roche (68) consiste à projeter le flux hydraulique sur les débris (68) lorsque ces débris (68) se détachent de la surface de coupe (40, 210, 302) et s'étendent au-dessus de celle-ci.
  17. Procédé suivant la revendication 14, dans lequel le trépan de forage (10) comprend une cavité (24) entre le corps de trépan (16) et la surface de coupe (40, 210, 302) et le flux hydraulique provient de l'intérieur de la cavité (24).
  18. Procédé suivant la revendication 17, dans lequel l'étape consistant à évacuer les débris de roche (68) implique le transport des débris de roche (68) dans la cavité (24), puis dans un passage annulaire formé entre le trépan à lames (10) et la paroi d'un trou en cours de forage par le trépan à lames (10).
EP88710035A 1987-10-13 1988-10-12 Trépan racleur avec buses pour le forage de formations plastiques Expired - Lifetime EP0322347B1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US10679387A 1987-10-13 1987-10-13
US106793 1987-10-13

Publications (2)

Publication Number Publication Date
EP0322347A1 EP0322347A1 (fr) 1989-06-28
EP0322347B1 true EP0322347B1 (fr) 1994-11-30

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ID=22313280

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Application Number Title Priority Date Filing Date
EP88710035A Expired - Lifetime EP0322347B1 (fr) 1987-10-13 1988-10-12 Trépan racleur avec buses pour le forage de formations plastiques

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EP (1) EP0322347B1 (fr)
CA (1) CA1302393C (fr)
DE (1) DE3852286T2 (fr)

Families Citing this family (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5199511A (en) * 1991-09-16 1993-04-06 Baker-Hughes, Incorporated Drill bit and method for reducing formation fluid invasion and for improved drilling in plastic formations
GB9621216D0 (en) * 1996-10-11 1996-11-27 Camco Drilling Group Ltd Improvements in or relating to cutting structures for rotary drill bits
US6068072A (en) * 1998-02-09 2000-05-30 Diamond Products International, Inc. Cutting element
AUPQ302599A0 (en) * 1999-09-22 1999-10-21 Azuko Pty Ltd Drilling apparatus
CN107956426A (zh) * 2017-12-07 2018-04-24 河南广度超硬材料有限公司 矿山开采专用金刚石钻头及其工作原理
CN113898296B (zh) * 2021-10-21 2023-11-10 湖南省矿宝精钻机械有限公司 一种四翼带球防堵水平头式刮刀钻头

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1169386B (de) * 1959-11-05 1964-05-06 Europ De Turboforage Soc Fluegelmeissel fuer Erdbohrungen
GB1548499A (en) * 1977-05-17 1979-07-18 Shell Int Research Rotary drilling bit for deephole drilling and method of manufacturing the same
BE903059A (fr) * 1985-08-13 1986-02-13 Diamant Boart Sa Trepan a gradins
GB2181173B (en) * 1985-10-01 1988-12-21 Nl Petroleum Prod Improvements in or relating to rotary drill bits
US4682663A (en) * 1986-02-18 1987-07-28 Reed Tool Company Mounting means for cutting elements in drag type rotary drill bit

Also Published As

Publication number Publication date
EP0322347A1 (fr) 1989-06-28
DE3852286T2 (de) 1995-06-22
DE3852286D1 (de) 1995-01-12
CA1302393C (fr) 1992-06-02

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