An improved hydraulic inner barrel in a drill string coring tool

The present invention relates to a coring tool as set forth in the pre-characterising portion of claim 1, and to a method of providing drilling fluid flow through a coring tool as set forth in the pre-characterising portion of claim 3.

A coring tool of the kind referred to as known from EP-A 0 134 586 comprises a channel communicating at its upper end with the lower end of a free axial space within the drill string, said channel completely bypassing the inner tube. After a valve ball has been dropped into the axial space within the drill string for closing the actual space at its lower end fluid flowing within the actual space being diverted to a pressure chamber of the piston means for providing upward longitudinal displacement of said inner tube.

Its the object of the invention to provide a coring tool and a method for providing drilling fluid flow through a coring tool allowing to flush the interior of the inner tube prior to initiation of a coring operation and thereafter to activate the tool to break and retrieve the core at a selected time during the coring operation.

The coring tool according to the invention is being constructed as claimed in claim 1, and the method according to the invention comprising the steps as claimed in claim 3.

These and other features of the invention may be better understood by now turning to the following figures, wherein like elements are referenced by like numerals.

BRIEF DESCRIPTION OF THE DRAWINGS

• Figure 1 is a longitudinal sectional view of a drill string used in a coring operation which incorporates the improved invention.
• Figure 2 is a cross-sectional view of the drill string of Figure 1 at a first stage of operation.
• Figure 3 is a cross-sectional view of the drill string of Figures 1 and 2 at a second stage of operation.

The present invention, including its mode and manner of operation, is better understood by considering the above figures in light of the following detailed description.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The invention is an improved externally powered mechanism for activating core catchers within coring tools or any other downhole tool. Activation of the mechanism, and indirectly of the core catcher, is externally precipitated and not dependent upon any type of coaction with the core, or dependent in any manner upon the action of gravity. One prior art method for externally powering a core catcher is shown and described in EP-A 0 134 586. While the apparatus and methodology disclosed within that application is highly satisfactory and represents a substantial improvement over the prior art, the design can be further improved, particularly with respect to its versatility, reliability, simplicity and economy of fabrication. The structure and method of operation of the improved mechanism can better be understood by now turning to consider in detail the illustrated embodiment.

Turn first to Figure 1, which is a broken cross-sectional view of a portion of a drill string, such as used in a coring operation, which drill string incorporates the improved invention. The drill string, generally denoted by reference numeral 10, includes an outer tube 12 threadedly coupled in a conventional manner to an outer tube sub 14. Although not shown in the figures, outer tube 12 longitudinally extends downwardly in the drill string and is ultimately coupled through additional subsections to a coring bit (not shown).

Beginning at the top of drill string 10, safety joint box 8 is conventionally coupled, by means not shown, to a safety joint pin 16. Safety joint pin 16 in turn is threadably coupled to a swivel-assembly 18. Safety joint 16 and swivel assembly 18 are concentrically disposed within an interior bore defined by safety joint box 8 and outer tube sub 14. Swivel assembly 18 includes an upper member 20, which is threadably coupled at its upper end to safety joint pin 16, and which is rotatably coupled at its opposing lower end to a rotational member 22 by means of a conventional ball bearing assembly 24. Ball bearing assembly 24 includes a plurality of spherical bearings 26 captured within a cylindrical bearing raceway 28, which in turn is disposed within mating cylindrical indentations defined within upper member 20 on one hand, and rotational member 22 on the other. The lower portion of upper member 20 is also threadably coupled to a bearing retainer nut 30 while the lower portion of rotational member 22 is coupled to a pressure relief sub 32. Pressure relief sub 32 and retaining nut 30 retain bearing assembly 24 within swivel assembly 18. Therefore, as safety joint box 8, and outer tube sub 14, and outer tube 12 rotate during the drilling operation, safety joint pin 16 and upper member 20 will. rotate with them. However, bearing assembly 24 allows pressure relief sub 32 to be rotationally fixed with respect to the rock formation (hence rotationally free from outer tube 12), and longitudinally fixed with respect to outer tube 12.

In the preferred embodiment sub 32 includes a pressure relief valve 34 axially disposed about and concentric with the upper portion of sub 32. Valve 34 is a cylindrical element slidingly disposed over sub 32, and covering and sealing bore 36 defined through sub 32. Valve 34 includes a plurality of depending fingers 35 longitudinally extending downwardly outside of sub 32 toward piston 44. As described below, piston 44 will ultimately abut finger 35 and force valve 34 upward, thereby uncovering bore 36 and allowing pressure within axial bore 38 to be vented into annular space 40.

One other embodiment would show a pressure relief sub 32 which could include one or more conventional bursting disks disposed in corresponding radial bore 36. Normally, each bursting disk would seal its corresponding bore 36, thereby preventing the flow of any drilling mud or hydraulic fluid within axial bore 38 from escaping and flowing into annular space 40 between the exterior of pressure relief sub 32 and the interior of outer tube sub 14.

Pressure relief sub 32 continues longitudinally downward within drill string 10, and is threadably coupled to an inner mandrel 42. Inner mandrel 42 is also concentrically disposed within outer tube sub 14 and outer tube 12, and is furthermore telescopically and slidingly disposed within outer piston 44. Pressure relief sub 32 and outer piston 44 are maintained in a hydraulically sealed relationship with respect to each other by virtue of a circumferential conventional O-ring 47. Outer piston 44 in turn is disposed concentrically within outer tube sub 14 and outer tube 12 and outside of inner mandrel 42. Similarly, inner mandrel 42 and outer piston 44 are maintained in a hydraulically sealed relationship with respect to each other by virtue of a circumferential conventional O-ring 46. Outer piston 44 longitudinally extends downwardly within drill string 10, past the end of inner mandrel 42, and is threadably coupled to an inner tube adapter 48. Inner tube adapter 48 in turn is threadably coupled to a conventional inner tube 50. The core is cut by the coring bit and disposed within inner tube 50. Thus, the entire interior structure of drill string 10-from pressure relief sub 32 to inner tube 50 is concentrically disposed within outer tube 12 and outer tube sub 14, and is rotationally fixed with respect to the rock formation, and rotationally free from outer tube 12.

Outer piston 44 is initially longitudinally temporarily fixed with respect to inner mandrel 42 by means of one or more locking dogs 52. Locking dogs 52 are disposed in radial bores 54 defined in inner mandrel 42, and extend into a corresponding and mating indentation groove 56 defined in the interior surface of outer piston 44. Locking dogs 52 are retained in the locked position of Figure 1, wherein outer piston 44 is locked by means of an inner piston 58. Inner piston 58 is telescopically and slidingly disposed within an axial bore defined through inner mandrel 42, and retained therein by means of a spring loaded coupling with a piston retaining nut 60. Piston retaining nut 60 in turn is threadably coupled to the lower end of inner mandrel 42. Inner piston 58 is retained within piston retaining nut 60, and thus inner mandrel 42, by means of a coil compression spring 62 circumferentially disposed outside of the lower end of inner piston 58, and extending from an interior lower shoulder 64 of piston retaining nut 60 to an upper outer shoulder 66 of inner piston 58. Inner piston 58 is hydraulically sealed with respect to inner mandrel 42 by means of a conventional circumferential O-ring 68.

Therefore, the space defined by axial bore 38 extends from the interior of drill string 10 above safety joint pin 16 longitudinally throughout the portion of drill string 10 shown in Figure 1, through inner mandrel 42, through inner piston 58 and downwardly through inner tube adapter 48 into the interior of inner tube 50. Inner tube adapter 48 is provided with a plurality of radial bores 70 which allow free hydraulic communication between axial space 38 and annular space 40. The lower end of inner tube adapter 48 is threadably coupled to a pressure relief plug 72. The pressure relief plug 72 defines an axial bore 74 to permit longitudinal hydraulic communication throughout the entire length of axial space 38 into inner tube 50.

Turn now to the illustration of Figure 2, which is a cross-sectional view of the drill string 10 of Figure 1 after the tool has been activated. As shown in Figure 1, continuous fluidic communication throughout drill string 10 is provided through axial bore 38. This allows the interior of inner tube 50 to be washed or flushed clean according to conventional well coring practices. However, when the coring operation is to begin, the well operator drops a first steel ball 76 into the drill string. Ultimately steel ball 76 will come to rest against seat 78 defined on the upper interior end of pressure relief plug 72. Fluidic communication with the interior of inner tube 50 will now be prohibited. The hydraulic fluid being pumped from the well surface into the interior of drill string 10 will continue through axial bore 38, but will be diverted within inner tube adapter 48 through ports 70 into annular space 40 between inner tube 50 and outer tube 12.

When the coring operation has been completed, and it is desired to break and retrieve the core from the rock formation, a second ball 80 is dropped into axial bore 38 from the well platform. Again, second ball 80 will ultimately come to rest against a seat 82 defined in the upper end of inner piston 58. The further escape of hydraulic fluid from axial space 38 into annular space 40 is now temporarily prohibited. Pressure will now begin to rise within axial bore 38. As the pressure increases, piston 58 and ball 80 begin to be forced downwardly against the resilient force of spring 62. As spring 62 compresses, outer circumferential indentation groove 84 defined in the outer surface of inner piston 58 will ultimately become aligned with dog 52. Meanwhile, the increased pressure within axial space 38 will be communicated by virtue of a plurality of radial bores 86 defined through pressure relief sub 32 which bores 86 communicate with an interior expansion space 88 of outer piston 44. This will exert a pressure within space 88 tending to longitudinally force outer piston 44 upwardly. However, outer piston 44 will remain locked in position by dog 52 until such time as inner piston 58 has been downwardly longitudinally compressed to align indentation 84 with dog 52. At this point dog 52 will snap into indentation 84, being urged therein by the upward force exerted upon outer piston 44.

Outer piston 44 will now be unlocked and free to be longitudinally displaced upwardly within drill string 10. As outer piston 44 is longitudinally forced upwardly by the injection of pressurized hydraulic fluid into space 88, inner tube 50, which is threadably coupled through inner tube adapter 48 to outer piston 44, will similarly be drawn upwardly.

This upward movement of inner tube 50 can then be used to activate other downhole tools, such as core catchers.

Turn now to Figure 3, wherein piston 44 is shown in the upwardly locked position. The expansion of outer piston 44 is limited by the abutment of the top of piston 44 with fingers 35 and the longitudinal upward disposition of valve 34 until it in turn abuts shoulder 90. At this point bore 36 is uncovered and the pressure within axial bore 38 equalizes with that in annular space 40. At this point the core catcher activation will have been completed, and hydraulic flow restored outside of inner tube 50.

In the illustrated embodiment a fully expanded locked position is shown and is achieved by defining an interior indentation 92 within outer piston 44 similar to that defined by interior indentation 56, but longitudinally disposed below indentation 56 by a predetermined distance. Lower indentation 92 will move upwardly to become at least even with dogs 52 during the expansion of outer piston 44. After valve 34 has been activated, the hydraulic pressure within axial space 38 will decrease and compression spring 68 will tend to urge inner piston 58 upwardly and force locking dogs 52 radially outward. As piston 44 falls, realigning the locking indentation 92 with dogs 52, dogs 52 are forced into the locking indentation 92, thereby longitudinally fixing outer piston 44 with respect to outer tube 12, and allowing inner piston 58 to fully expand under the force of compression spring 62.