INFLATABLE CARTRIDGE ASSEMBLY

Abstract: An inflatable cartridge assembly includes a mandrel (20) having a substantially axially-extensible core member (22) and two end abutments (32) one on each end of the core member and extending radially outwardly therefrom. An inflatable and radially expandable sleeve (10) is positioned around the mandrel (20) and bonded in a fluid tight relation at its outwardly directed end faces to inwardly directed end surfaces of the end abutments. At least one aperture (30) is provided on the mandrel for admission of a pressurized fluid to the interior of the sleeve (10) to expand the sleeve. In assembling the cartridge, the sleeve may be formed on the mandrel by molding an elastomeric material directly to the mandrel in a manner such as casting.

Description: INFLATABLE CARTRIDGE ASSEMBLY The present invention relates generally to an inflatable cartridge assembly. More specifically, the present invention relates to a substantially axially non-extensible mandrel and an expandable sleeve positioned around the mandrel and bonded thereto. Inflatable cartridge assemblies have heretofore been employed in a number of applications such as splitting concrete and rock and have also been employed as well packer In the splitting of hard brittle materials, mechanical splitters are safer than explosives. A mechanica splitter is inserted in a bore in the rock and exerts pressure against the bore surface. In that application, an inflatable cartridge assembly is advantageous over the use of the conventional "Darda" wedge and feather arrange¬ ment (an example of which is disclosed in United States Patent No. 4,114,951) because, for one thing, the Darda unit is cumbersome to use. In the well drilling industry the cartridges and versions thereof form the principal component of an inflatabl packer. . Such packers which are used to seal zones in a well are generally used in conjunction with fracturing, cementing, treating, or testing operations. The conventional inflatable units used for either rock splitting or well packing suffer, however, from several shortcomings. From the standpoint of tool life, conditions at the ends of the inflatable sleeve are critical, and these conditions are a function of the method of securing the sleeve ends. Mechanical clamping is the traditional method of securing these ends and this is disadvantageous because excessive stresses can be imposed on the expandable sleeve in the clamping zone and because the clamping force will gradually diminish due to a stress relaxation of the sleeve / _.-^- 2___ ■ v!p material. Also, the longitudinally inner ends of means used for securing the sleeve tend to be relatively sharp thus producing a stress concentration in the sleeve in this critical zone which tends to reduce cycle life. Moreover, the clamping means take up a substantial amount of sleeve length thereby shortening the effective length of sleeve usable for expansion against the bore surface. Other inflatable unit configurations, which are undamped and may be bonded, suffer from a thin walled sleeve configuration. A thin walled sleeve is disadvantageous when one considers both phases of a splitting cycle. During pressurization, up to the point of fracture initiation, a large sleeve thickness is desirable adjacent the end abutment to inhibit extrusion, and minimize stresses thus produced, through the annulus surrounding these abutments. After fracture, some users will continue the flow of fluid into the cartridge, albeit at a reduced pressure, in order to widen th fracture. This is done especially in reinforced concrete to expose the reinforcing rods for subsequent burn cutting. Thus a large wall thickness is desirable along the entire length of a splitter sleeve to minimize extrusion through the fracture. It has, therefore, been considered desirable to develop a new and improved inflatable cartridge assembly, usable for both rock splitting and well packing applications, which would overcome the foregoing difficulties while providing better and more advantageous overall results. An inflatable cartridge assembly according to the present invention includes a mandrel having a substantial axially non-extensible core member and two end abutments that extend radially outwardly therefrom. An inflatable and radiallyexpandable sleeve is positioned around the mandrel and is bonded in a fluid tight relation at its outwardly directed annular end faces to inwardly directed annular end surfaces of the end abutments in a bonding zone. At least on aperture is provided on the mandrel to admit a pressurized • fluid to the interior of the sleeve in order to expand the sleeve. A method for producing an inflatable cartridge assembly includes positioning the mandrel in a mold cavity and molding an elastomeric material around the mandrel. The elastomeric material is cured to form the expandable sleeve with the sleeve becoming bonded to the mandrel at the end abutments thereof. The assembly is thereupon removed from the mold cavity. The principal focus of the present invention is the provision of an improved inflatable cartridge assembly. One advantage of the invention is the provision of a less compli¬ cated, and hence less expensive, cartridge assembly. A further advantage of the invention is the provision of a cartridge assembly which is usable at both.the lower pressure required in well packing and the higher pressures required in rock splitting. A still further advantage of the invention is the provision of a cartridge assembly in which the sleeve can be reinflated numerous times without failing at its bonding zone with the mandrel. The invention may take form in several embodiments which will be described in detail in the specification, and wherein: FIGURE 1 is a longitudinal cross-sectional view of an inflatable cartridge assembly according to the present . invention; FIGURE 2 is a transverse cross-sectional view along line 2-2 of the cartridge assembly of FIGURE 1; FIGURE 3 is a sideelevational view, partly in cross section, of one apparatus used to make the inflatable cartrid assembly of the present invention; FIGURE 4 is a longitudinal cross-sectional view of a portion of another inflatable cartridge assembly according to the present invention; -£ffI OMPI FIGURE 5 is a longitudinal cross-sectional view of another inflatable cartridge assembly according to the presen invention; FIGURE 6 is a longitudinal cross-sectional view of still another inflatable cartridge assembly according to the present invention; and, FIGURE 7 is a transverse cross-sectional view of another inflatable cartridge assembly according to the present invention. With reference to the drawings, wherein the showings are for purposes of illustrating the embodiments of the invention only and not for purposes of limiting the same, FIGURE 1 shows the preferred embodiment for splitting applications in which a sleeve 10 substantially surrounds a mandrel 20. The mandrel 20 includes a core member such as a cylinder 22 having a through bore 24, two threaded ports 26, 28, and at least one transverse aperture 30. A packer embodiment of the invention can also take the form of FIGURE 1. In that case the bore 24 of the core member 22 would probably be larger as would be the port threa diameters 26, 28. Also, the ports 26, 28 could connect to sections of a pipe string instead of to the fittings shown. In other embodiments, the cartridge would form one component of a packer assembly, with the threaded ports being replaced by straight threaded connection means for joining to other components. The mandrel 20 also includes a pair of end abutment 32, one being provided on each end of the core cylinder. The end abutments 32 have a through hole 34 and are joined to the cylinder by brazing or other means. Inwardly directed end surfaces 36 of the abutments 32 are relieved with a large radius at one outside edge to minimize sleeve stresses and are bonded to the ends of an elastomeric sleeve 10. The end surfaces 36 are shown to be flat and perpendicular to the longitudinal axis of the core cylinder 2 but they may take a conical form or an irregular form. Alternatively, it would also be possible to manufacture a "blind" type mandrel (not illustrated) in which case the bottom end abutment would be constructed with a blind bore instead of a through bore. Port 26 is connected to a hose fitting member 50 which in turn is in fluid communication with a fluid pressurization means such as a pump 60 through a fluid line 62. One suitable standard hand operated pump 60 weighs fift pounds and can perform the splitting cycle in less than a mi Alternatively, the fluid pressurization means may be an air powered hydraulic pump. A plug member 40 is threaded into the second port 28 to close that end. Where appropriate, a number of cartridges could be connected in series for use in longer bores. With a cartridge of approximately twenty inches in length, a plurality of apertures 30 is useful to prevent the trapping of the hydraulic fluid after depressurization of the sleeve. Short cartridges may require only one apertu 30. Upon pressurization in a bore, it has been found that the sleeve is under a state of pseudo-hydrostatic stress. This is true even when the sleeve is made of the preferred hard material (approximately ninety A durometer) . Thus, the pressure delivered to a bore surface 66 by sleeve 10 (as illustrated in dashed outline in FIGURE 1) is approximately equal to the fluid pressure exerted on the inn surface of the sleeve. When pressurized, infinitesimal portions of the elastomeric sleeve 10 are ' pproximately under a state of triaxial compression and the accompanying shearing stresses acting on the faces of these portions are relatively small. In a fluid where a truer hydrostatic condition would exist, these shearing stresses would be clos to zero. Sleeve portions at the bonded surface are also subjected to normal and shearing stresses and here too the OMPI shearing stresses are small because of the quasi-fluid nature of the sleeve material. However, the state of stress at the bonded interface is complex because of the restrained condition of the sleeve at that zone. It is strongly suspected, however, that the relatively high pseudo-hydrostatic stress, being compressive and acting perpendicular to the bonded surface, overcomes the tendency for other stresses, produced by the pressurizing fluid on the sleeve 10, to disrupt the bond between the sleeve and the end abutments 32. This provides an effective way of securing the ends of the sleeve 10 to the end abutments 32 without the previously outlined disadvantages of a clamping arrangement. Tests under elevated pressures including pressures at 5,000 psi in a bore show that a properly made bond will not fail. Failure after repeated cycling appears usually to occur through means of crack propagation in the inflatable sleeve at locations other than along the bonded interface. Successful results are achieved with sleeve durometers ranging from eighty A to ninety-five A with the best results being achieved at the higher end of this range. The sleeve 10 preferably extends longitudinally substantially only as far as the inwardly directed end faces 36 although, if the sleeve is molded directly to the mandrel, a flash may be left on the sides of the end abutment 32. It is also preferred that the only bonding between the sleeve 10 and the mandrel 20 take place on the inwardly directed end surfaces 36 of the end abutments. It has been found that with such a bonding the sleeve 10 has greater life than one where the bond also extends onto the core cylinder 22 by a length of approximately three-eight of an inch. The sleeve member 10 is an elastomer preferably made of a hard (eighty-five A to ninety-five A durometer) castable polyester type urethane which has.the necessary resistance to oil and the necessary strength to sustain the high pressures encountered in use. In use, the inflatable cartridge assembly of the present invention may be exposed to press.ures of up to approximately 4,500 psi during rock splitting operations an somewhat lower pressures, on the order of approximately 1,000 to 2,000 psi, during well packing operations. For splitting applications the core cylinder 22 is preferably steel tubing having three-quarters inch O.D. and three-sixte inch wall thickness. The end abutments 32 are steel members one ' nd one-half inches O.D. by three-quarter inches long. The ends of the core cylinder 22 may be threaded to receive one-quarter inch tapered thread fittings, such as at 40 and It would also be possible to utilize sealed straight threaded fittings or other connectors for this purpose. The outer diameter of the mandrel 20 is thus one and one-half inches and generally speaking a bore 66 of approximately one and five-eighths inches diameter is drilled into the material in which the cartridge assembly will be used. Splitting type cartridges typically have a length ranging from six inches tois.enty-eight inches depending upon the application for which they are intended. Packer-type cartridges would normally be longer. The total force exerte is a direct function of the sleeve length of the pressurized cartridge. The type of bore in which the cartridge is inserted should be carefully considered since large voids in the bore or a bore of insufficient length may cause rupture tool. Of course it would also be possible to reinforce the sleeve 10 with suitable means. With reference now to FIGURE 3, which illustrates one fabrication technique for the cartridge assembly of the present invention, a mandrel 20 ready for application of the sleeve 10 is placed inside a tubular mold 70. The mold is provided with an aperture 72, through which a hardenable elastomer compound (preferably urethane) which will become t sleeve 10 will be poured, and a positioning member such as a button 74. The bore of the mold is treated with a suitable mold release material. A plug 86 and a nipple 88 can be threaded on the mandrel 20 to seal the mandrel threaded openings prior to molding. The nipple 88 also simplifies handling. Sealing means (not illustrated) are applied to the radial holes 30 in the mandrel 20 to prevent casting material from entering such holes during the casting process. These means are subsequently removed or rendered inoperative. The end abutments 32 of the mandrel 20 are cleaned with a solvent and grit-blast. A coating 82 of a conventiona urethane to steel adhesive may be applied to the end surfaces 36 and the cylindrical portion of the end abutments 32 to enhance the bonding process. A mask 80 may then be secured around end portions of the core cylinder 22 adjacent the end abutments 32. The mask 80, which is preferably a PTFE-ty tape having an adhesive backing, is approximately 3 mils thic Also, a mold release agent 84 may be coated onto the core cylinder 22 between the masks 80 to prevent adhesion of the sleeve 10 to the core cylinder 22. If used, the mask 80 remains a permanent part of the final product having serve its function of insuring the uniformity of the bond, such as by preventing the migration of the mold release agent 84 (if used) into the bonding zone. Prior to actual pouring, the mold 70 and mandrel assembly 20 are brought up- to the necessary temperatures in a conventional molding oven, and a heated conventional uretha casting material, consisting of a prepolymer, a curative agen and a pigment, is degassed and poured into the mold according to theconventional practice. " Standard curing methods are • observed after pouri ' ng. The riser produced by extra casting material at the aperture 72 can be cut away after the curing. During the curing process, shrinkage of the sleeve material (greatly magnified in FIGURE 1 for clarity) will occur. The corresponding reduced outer diameter of the major portion of sleeve length allows for greater ease of insertion of a cartridge into a slightly curved rock bore. Moreover, OMPI the corresponding residual circumferential strain will help urge a depressurized sleeve 10 back to its starting position It has been found that a diametral clearance of .0 inches between the end abutments 32 and the mold inner diame works well for mandrel insertion and mold stripping and results in only a thin flash on the outer diameter of the en abutments 32. It would, however, also be possible to have a thicker flash over the end abutments 32 if this were considered necessary. With reference now to FIGURE 4, a first alternate embodiment of a sleeve 10' and a mandrel 20' is illustrated. In this configuration, a "blind"-type mandrel 20' is machine from one piece of bar stock and is provided with an angled aperture 30'. Pound for pound, the bar stock is much more economical than tubing. Also, machining from bar stock eliminates the step of brazing end abutments onto a core member. A snug fitting O-ring 96 could be placed around the mandrel 20' a short distance inboard of end abutment inwardl facing surfaces 36' (only the upper O-ring is shown) . It has been found that a standard O-ring 96 will not bond eithe to the sleeve 10' or to the mandrel 20' . The relief thus cr by the resulting reduced sleeve thickness over the O-rings 96 may ease the strain on the bond when the cartridge is pressurized in a bore. End surface 36' has a form at its outer radial reaches which may further reduce the stress level, on the outside diameter of the sleeve, beyond that of the configuration of FIGURE 1. Both end abutments of mandrel 20' are similarly contoured. With reference to FIGURE 5, a second alternate embodiment of a mandrel 20" has two end abutments 32" bonded to a ' sleeve 10" in an independent operation. This subassembly is subsequently placed on a core member 22" and is retained by snap rings 88. Pressurizing fluid in the mandrel 20" is sealed from the atmosphere by O-rings 90 in the end abutments 32". ' This embodiment is useful for field OMPI replacement of the sleeve subassembly. End surfaces 36" are shown meeting mandrel 20" at an acute angle A and this fo may provide the bond with an additional measure of strength over that of the configuration of FIGURE 1. Angle A may also be obtuse but tests have shown that cartridge life is compromised when this angle becomes too large. With reference to FIGURE 6, a mandrel 20 , , , has two tubular core member end sections 22 • * ' which are swaged to a length of wire cable 23. This provides mandrel flexibility in a curved bore. Prior to molding a sleeve 10' " around the mandrel 20 l , r , the cable 23 could be sealed with a compound to prevent sleeve material from flowing into the interstices of the cable. Fluid communication between the apertures 30' * ' of the mandrel 20' ' * takes place through the interstices of the cable 23. The method of molding the sleeve on the mandrel is advantageous because it enables the sleeve to conform to the outer geometry of various types of mandrels. Finally, FIGURE 7 illustrates an embodiment that is useful for preventing the failure of the cartridge at a maj void by bridging over voids in the bore surface 66. Curved strips 92, which could be made from steel tubing, and which have rounded side edges as shown (edges at the ends would be similarly rounded) , could be secured to the cartridge and the whole assembly inserted into the bore 66. Preferably, the strip lengths would be shorter than a sleeve 10"" length by approximately one inch at each end. A sleeve outer surface could be lathe cut over the length of the strips 92 to nest the strips and to keep the assembled diameter "D" from exceeding that of the end abutments. This arrangement could provide other benefits such as providing a desired directionality to the ensuing fracture in a rock or preventing an undesired fracture direction. Similar results can be achieved with a length of tubing having only one longitudinal slit in place of the pair of strips (not illustrated) . Likewise somewhat larger diameter strips covering the full length of the cartridge could be used, but this would have the disadvantage of requiring a larger diameter bore and would also permit more extrusion of the sleeve material at its ends due to the fact that the inner surface of the tubing is more slippery than the bore inner surface. In employing the splitter of this invention, a hole of the proper length and diameter is drilled in the rock to be split into which the splitting tool is then inserted. Fluid, such as hydraulic oil, is then pumped into the tool via a length of hose, causing the sleeve to expand. Pumping is continued until the sleeve expands sufficiently to cause the rock to crack, and cracking is noted a) visually; b) audibly; or c) by a drop in pressure. Following rock fracture, the tool is depressurized and extracted from the hole after which it can be employed again. Splitter tool utilization requires that: a) no part of the sleeve should be outside of the bore hole; b) the walls of the bore hole should not contain any voids or clay seams; and c) the recommended bore diameter must not be exceeded. Departure from these rules could result in tool failure caused by sleeve rupture.

Claims: Claims : 1. An inflatable cartridge assembly useful for delivering high pressures to the inside surface of an aperture or bore characterized by a mandrel including: a substantially axially non-extensible core member, and two end abutments, one being provided on each end of said core member and extending radially outwardly therefrom; an inflatable and radially expandable sleeve positioned around said mandrel, outwardly directed end faces of said sleeve being each bonded in a fluid tight manner to a respective inwardly directed end surface of said end abut¬ ments in a bonding zone, said core member and said abutments cooperating to inhibit longitudinal extension of said sleeve, and wherein the thickness of said sleeve, along most of its effective length, is greater than the corresponding radial thickness of a fluid cavity surrounding said core member, whe said sleeve is in an unexpanded position; at least one apertu provided on said mandrel for admission of a pressurized fluid to the interior of said sleeve to expand said sleeve and optionally a coating of adhesive provided on said "end abutmen to enhance the bond. 2. The cartridge of claim 1, characterized in that said core member is tubular and is provided with an interior cavity in the form of a cylindrical aperture extending the length of said core member and wherein at least one end of sa mandrel is provided with a screw threaded aperture. 3. The cartridge of claim 1, characterized in that said end abutments are relieved at an outer edge to minimize stresses on said sleeve during pressurization. 4. The cartridge of claim 1, characterized in that said sleeve material is of a hardness of at least .80 A durometer. 5. The cartridge of claim 4, characterized in that said sleeve is made of a urethane material. 6. The cartridge of claim 1, characterized by further comprising fluid pressurization means for selectively supplying a pressurized hydraulic fluid to said mandrel and therefore said sleeve to expand said sleeve. 7. The cartridge of claim 1, characterized in that the internal surface of said sleeve, in its unexpanded position, is over most of its effective length, in contrast with the outer surface of said core member. 8. The cartridge of claim 1, characterized in that the bonding between said expandable sleeve and said end abutments occurs during th formation of said cartridge as a hardenable elastomer is molded around said mandrel. 9. The cartridge of claim 1, characterized in that said two end abutments are restrained from outwardly directed longitudinal motion by mechanical means secured to said core member and wherein said fluid sealing means are provided between said end abutments and said core member. 10. The cartridge of claim 1, characterized in that said mandrel includes two end members and a central wire rope member secured therebetween. 11. The cartridge of claim 1, characterized by further comprising a longitudinally slit tubular bridging member, said member protecting said sleeve and also providing splitting directionality. 12. The cartridge of claim 11, characterized in that the outer diameter at the end portions of said sleeve is appreciably larger than over its longer central portion in order to nest said bridging member. 13. The cartridge of claim 1, characterized in that said inwardly directed end surfaces of said end abutments meet the core member at an angle no greater than 135°, said angle measured between corresponding intersecting lines on said core member and said end abutments, said lines being delineated in a longitudinal cross section of said cartridge, and said angle measured through the zone occupied by said sleeve. 14. The cartridge of claim 1, characterized in that there are provided means for creating a bonding zone during the formation of the cartridge when a hardenable elastomer, which will form said sleeve, is molded around said mandrel; and said sleeve is secured to said mandrel only by a continuous bond between said sleeve and said mandrel, said bond being provided only at the inwardly directed end surfaces of said end abutments, and over a length not exceeding one inch at each end of the ends of said core member adjacent said end abutments and over a portion of the outer surfaces of the said end abutments. 15. The cartridge of claim 14, characterized in that an outer diameter of said end abutments is equal to a nominal diameter of the cartridge. 16. A method for producing an inflatable cartridge characterized by providing a mandrel having a core member and two end abutments; positioning the mandrel in a mold cavity; pouring a hardenable elastomeric material into said mold cavity around said mandrel; curing said elastomeric material to form an expandable sleeve around said mandrel, said sleeve being bonded to said mandrel at said end abutments thereof; and removing the cartridge from said mold cavity. 17. The method of claim 16, characterized by further comprising coating inner end surfaces of said end abutments with an adhesive to enhance the bonding of said sleeve to said mandrel before said step of positioning said mandrel in said mold cavity. 18. The method of claim 16, characterized in that said mandrel contains at least one aperture which aperture is sealed during said step of pouring the hardenable elastomeric material to prevent said material from seeping into said aperture. 19. Use of a cartridge as in any one of claims 1-15, characterized in that the tool is inserted-into a straight drilled hole in a rock to be split, pumped up with a fluid which expands a sleeve surrounding a core member until said rock splits and then extracting said tool from sai rock. 20. Use of a tool as in claim 19, characterized i that during normal operation, a pseudo-hydrostatic state of stress acting on the sleeve at said bonding zone results in compressive stresses that are substantially perpendicular to said bonding zone, said compressive stresses being of a magnitude sufficient to prevent other type stresses induced by said pressurizing fluid from producing bond separation at said bonding zone whereby said bond remains intact during expansion of said sleeve in a bore. OMPI

Inventors: CENTURY BERNARD AMOS, CENTURY, BERNARD, AMOS
Applicants: CENTURY BERNARD AMOS, CENTURY, BERNARD, AMOS
Application year: 1984
Main classification: E21B33
IPC codes: E21B33, E21C37