GB2293843A

GB2293843A - Downhole tool assembly

Info

Publication number: GB2293843A
Application number: GB9525208A
Authority: GB
Inventors: George Telfer
Original assignee: Nodeco Ltd
Current assignee: Nodeco Ltd
Priority date: 1992-08-18
Filing date: 1993-08-18
Publication date: 1996-04-10
Anticipated expiration: 2013-08-18
Also published as: GB2293843B; GB9525208D0

Abstract

A downhole tool assembly 14 employed in the drilling of a well includes a sleeve 24, a tube 18 partially located within the sleeve 24, a running tool sub-assembly 20 below the tube 18, and a tubular extension 22 depending from the running tool sub-assembly 20, the external diameter of the tube 18 being equal to that of the tubular extension 22. A junk bonnet 30 in the form of an annular seal fits around the tube 18 and inside the sleeve 24. The junk bonnet 30 is provided with sliding fluid seals 42, 44, 48, 50 which seal against the external surface 19 of the tube 18, and against the bore 25 of the sleeve 24. A longitudinal fluid passage 52 links opposite ends 54, 56 of the junk bonnet 30. The passage 52 is sealed in use by a plug 60 or other suitable valve. An annular volume "C" below the junk bonnet 30, between the tube 18 and the sleeve 24, and above a seal 26 forming part of the downhole tool assembly 14 is filled through the passage 52 with hydraulic oil during setting-up and prior to closure of the passage 52 by the plug 60. This hydraulically locks the junk bonnet 30 in place on the downhole tool assembly 14, without reliance on any mechanical fastening, and yet free of susceptibility to being dislodged by normal operational movements of the downhole tool assembly 14. <IMAGE>

Description

"ImDrovements in or relating to Protective Arrangements This invention relates to protective arrangements, and relates more particularly but not exclusively to protective arrangements for downhole tool assemblies employed in the drilling of wells.

In the drilling of wells intended for exploration of subterranean formations and/or the eventual recovery of hydrocarbons or other minerals, much of the work involves drilling of the well. However, from time to time it is necessary to lower a tool assembly down the well for the accomplishment of related operations. For example, a liner running and cementing operation may be necessary in the course of drilling a well. Such tool assemblies have varying degrees of complexity, and frequently involve fluid flow passages and/or relatively movable components or sub-assemblies.

Proper functioning of such tool assemblies can be disrupted by the entry of drilling debris into the mechanism or fluid passages. A form of protective arrangement for obviating such debris-induced disruption is known as a junk bonnet", and takes the form of a cap intended to shield the tool assembly from descending debris. However, known forms of junk bonnet do not provide a fluid seal, and are liable to be dislodged by movement of the drill pipe as part of operation of the tool assembly. These problems allow debris to enter the tool assembly, and result in failure of the protective arrangement.Further, the known forms of junk bonnet have a relatively large outside diameter which restricts fluid circulation in the annulus between the drill pipe and the casing, and which hinders easy removal of the tool assembly from the well when a large amount of cuttings and drilling debris has accumulated in the annulus.

It is therefore an object of the invention to provide a protective arrangement for a downhole tool assembly which obviates or mitigates these problems. Also the invention seeks to hydraulically lock the junk bonnet in position without reliance on mechanical fastening.

According to a first aspect of the present invention there is provided a downhole tool assembly comprising a sleeve member, a tube member partially located within said sleeve member, a running tool sub-assembly below the tube member and a tubular extension member depending from the running tool sub-assembly, characterized in that the external diameter of the tube member is equal to the external diameter of the tubular extension member.

Embodiments of the present invention will now be described by way of example with reference to the afcompanying drawing, the sole Figure of which is a longitudinal elevation of a length of casing and hanger/liner enclosing a downhole tool assembly incorporating a protective arrangement in accordance with the invention, the right half of the Figure being radially sectioned as far as the centre-line of the assembly, and the left half of the Figure being conventionally radially sectioned (ie to show the radially external surface of the radially innermost entities of the assembly).

Referring to the Figure, there is shown a downhole section of previously drilled well lined with 95/8 inch (244.5 millimetre) casing 10. A 7 inch (177.8 millimetre) liner 12 is shown run within the casing 10 on the lower end of a liner running/cementing downhole tool assembly 14 of known form. The tool assembly 14 is suspended within the casing 10 on the lower end of a drill pipe 16.

Those parts of the tool assembly 14 which are of significance to the present invention are a setting tool tube member 18 having an inside diameter of 71.4 millimetres and an external surface 19 with a diameter of 100 millimetres, a running tool sub-assembly 20 below the tube member 18, and a tubular stinger extension member 22 depending from the sub-assembly 20.

The tubular extension member 22 of the tool assembly 14 has an external diameter of 100 millimetres, ie the same external diameter as the external diameter of the tube member 18. The tool assembly 14 further comprises a coaxial PBR (polished bore receptacle) sleeve member 24 to the lower end of which the liner 12 is attached, coaxially with the sleeve member bore 25. Mounted within the lower end of the sleeve member 24 is an annular seal 26 suspended on a 7 inch (177.8 millimetre) nipple 28 forming the lower end of the sleeve member 24. The annular seal 26 forms a sliding fluid seal on the tubular external surface of the tubular extension member 22 of the tool assembly 14.

To protect the tool assembly 14 from having its correct operation disrupted by cuttings and other drilling debris falling into it, the tool assembly 14 is provided with a protective arrangement in the form of a junk bonnet 30 which is an annular seal assembly fitted around the tubular external surface 19 of the tube member 18 and within the tubular bore 25 at the upper end 32 of the sleeve member 24 to provide a sliding fluid seal to each of these surfaces.

The junk bonnet 30 comprises two axially elongate hemi-annular segments 34 mutually secured by bolts 36, with gaskets 38 clamped between mating faces of the segments 34 to inhibit end-to-end fluid leakage.

The inner surface 40 of the annular junk bonnet 30 is provided with a lower inner seal 42 in the form of an elastomeric O-ring mounted within a circumferential slot extending around the inner surface 40, and is further provided with a pair of upper inner seals 44 each in the form of an elastomeric O-ring mounted within a respective circumferential slot extending around the inner surface 40.

The outer surface 46 of the annular junk bonnet 30 is provided with a pair of lower outer seals 48 each in the form of an elastomeric O-ring mounted within a respective circumferential slot extending around the outer surface 46, and is further provided with a pair o; upper outer seals 50 each also in the form of an elastomeric O-ring mounted within a respective further circumferential slot extending around the outer surface 46.

Each of the O-ring seals 42, 44, 48, and 50 stands slightly proud of its respective mounting slot to form a sliding seal with the external surface 19 of the tube member 18 and with the bore 25 of the sleeve member 24, respectively. A longitudinal fluid passage 52 extends between and hydraulically links the lower axial end 54 of the junk bonnet 30 with its upper axial end 56, for a purpose detailed subsequently. A transverse fluid passage 58 links the longitudinal fluid passage 52 with the inner surface 40 between the upper and lower inner seals 44, 42, and with the outer surface 46 between the upper and lower outer seals 50, 48, for a purpose also to be detailed subsequently. The longitudinal fluid passage 52 can be selectively blocked or opened for the passage of fluid through the junk bonnet 30 between its axially opposite ends 54 and 56, by the insertion or removal of a screw-threaded plug 60.

Setting up of the above arrangement will now be described.

At the well surface, components of the tool assembly 14 are put together in known manner, with the annular seal 26 mounted within the nipple 28 in the lower end of the sleeve member 24, and the tubular stinger extension member 22 threaded therethrough to form a sliding fluid seal therewith.

The pair of junk bonnet segments 34 are assembled around the tube member 18 of the tool assembly 14, thereby avoiding potential problems in having to thread the junk bonnet 30 over the pipe connector 62 by which the tube member 18 will be attached in use to the drill pipe 16. (The inner seal rings 42 and 44 can be fitted over the pipe connector 62, since these rings are elastic and circumferentially stretchable). The rings 42 and 44 are fitted into their slots on the inner surface 40, the gaskets 38 are placed between the mating faces of the segments 34 which are then mutually clamped by the bolts 36, the outer seal rings 48 and 50 are fitted into their slots on the outer surface 46, and the thus-assembled junk bonnet 30 is slid down the external surface 19 of the tube member 18 to be inserted into and rest partly within the bore 25 at the upper end 32 of the sleeve member 24.

This arrangement forms an annular volume, denoted "C" in the Figure, which is externally bounded by the bore 25 of the sleeve member 24, internally bounded by the exterior surface 19 of the tube member 18 in conjunction with the exterior of the tubular extension 22 and the tool sub-assembly 20 linking them, bounded at the lower end by the annular seal 26, and bounded at the upper end by the lower axial end 54 of the junk bonnet 30.

While the longitudinal fluid passage 52 through the junk bonnet is temporarily open by the absence of the plug 60, the annular volume "C" is filled with an appropriate oil or other suitable hydraulic fluid, such as to exclude all air from volume "C". (Total filling can be assisted by pushing the junk bonnet 30 down a short distance into the oil-filled sleeve member 24 such to force oil out of the passage 52). Volume "C" is then sealed by tight insertion of the plug 60.

Since the external diameters of the tube member 18 and of the tubular extension 22 are the same where they pass through the respective sliding fluid seals 44 and 26, longitudinal movement of the tube member 18 together with the tool sub-assembly 20 and the tubular extension member 22 with respect to the sleeve member 24 and the seal 26 mounted therein causes no change in the volume of the annular volume "C". Thus the junk bonnet 30 is hydraulically locked in its position plugging the upper end 32 of the sleeve member 24, without reliance on any mechanical fastening or the like, and yet free of susceptibility to being dislodged by normal operational lifting/lowering of the sub-assembly 20 within the downhole tool assembly l4.

When the combination of the tool assembly 14 and the junk bonnet 30 (set up as described above) is coupled to the drill pipe 16 and lowered downhole to an operational depth in the already-drilled well for the performance of a drilling associated operation therein (liner running and cementing in this example), the junk bonnet 30 prevents cuttings or other debris from dropping into the tool assembly 14, thus to serve as a protective arrangement therefor.

In the downhole tool operating configuration illustrated in the Figure, fluid can be circulated down the bore of the drill pipe 16 and the bore of the tube member 18, and through the bores of the tool sub-assembly 20 and of the tubular extension member 22, to discharge from the bottom (not shown) of the liner 12 and return uphole to the surface through the annulus between the tube member 18 and the casing 10. During such circulation, the volume "C" remains hydraulically sealed and protected from debris. The minimal outside diameter of the junk-bonnet 30 (less than the outside diameter of the sleeve member 24) obviates obstruction of circulation in the annulus between the tube member 18 and the casing 10.

Prior to cementing of the liner 12 in its intended place in the well, the liner running tool sub-assembly 20 is unscrewed from its initial (as set-up) screw attachment 64 to the sleeve member 24 of the downhole tool assembly 14 by anti-clockwise (as viewed from above) rotation of the drill pipe 16, and lifted by a metre or so to check for proper release of the screw attachment 64. Such operation of the downhole tool assembly 14 commonly causes entry of debris in prior art configurations of junk bonnet, but with the junk bonnet 30 of the present invention, such debris entry is entirely inhibited since the junk bonnet 30 fully seals the top of the sleeve member 24 and remains hydraulically locked in place.

At the end of the liner cementing operation, the drill pipe 16 and the running tool sub-assembly 20 are pulled from the well, leaving the sleeve member 24 and the liner 22 downhole. To achieve such withdrawal, it is necessary first to break the hydraulic locking of the junk bonnet 30 in the upper end 32 of the sleeve member 24. To this end, a longitudinal hydraulic bypass slot 66 is cut in the exterior surface of the tube member 18, at a location thereon sufficiently far down as to have no effect on setting-up, running, and cementing operations, but effective on sufficient lift being imparted to the drill pipe 16 as to run up the inner surface 40 of the junk bonnet 30 to an extent that the slot 66 bypasses the inner seals 44, thus breaking the hydraulic lock and freeing the junk bonnet 30.

There is a known problem in well drilling operations that the top of the cemented-in liner may accumulate such an excess of debris that the bypass slot 66 would become blocked before it as effective to break the aforementioned hydraulic locking of the junk bonnet 30.

To obviate or mitigate this hazard, the upper axial end 56 of the junk bonnet 30 is optionally formed as a conical reamer, while the lower axial end 54 is formed with one or more notches 68 engageable by one or more matching axial lugs 70 on the upper end of the sub-assembly 20. The notches 68 and the lugs 70 function as a dog clutch to enable the junk bonnet 30 to be lifted and rotated to back-ream its way through the excess of debris.

To guard against continued jamming of the junk bonnet 30 despite such provision for back-reaming and/or failure of hydraulic lock breaking, the lower end of the tube member 18 is provided with an emergency release coupling 72 which connects the tube member 18 with the sub-assembly 20. The coupling 72 comprises an external sleeve 74 covering and hydraulically sealing the mutual junction of the tube member 18 with the sub-assembly 20, and a radial port 76 hydraulically linking the normally isolated bore through the tool assembly 14 with the annular volume "C". The sleeve 74 mutually secures the mating halves of the coupling 72 by means of an array of shear screws 78 selected to part upon application trough the drill pipe 16 and the tube member 18 of a predetermined lift force substantially in excess of lift forces applied in normal operation of the downhole tool assembly 14.

Such overlift fractures the shear screws 78, parts the emergency release coupling 72, and vents volume "C" through the radial port 76. This breaks the hydraulic locking of the junk bonnet 30 and also provides additional circulation for debris clearance.

The transverse fluid passage 58 linking the fluid passage 52 and the inner and outer junk bonnet surfaces 40 and 46 allows testing of the junk bonnet seals 42, 44, 48 and 50 on a suitable test rig (not shown) prior to. setting-up and use of the junk bonnet 30.

The above described exemplary embodiment of downhole tool assembly and of the protective arrangement therefor have been described in the context of a substantially vertically drilled well. However, such arrangements can also be employed in inclined and horizontal wells, and in analogous situations such as tunnelling and mining.

The present invention is not restricted to the exemplary embodiments described above, nor to the optional variations thereof also referred to, and other modifications and variations can be adopted without departing from the scope of the invention as defined in the appended Claims.

Claims

1. A downhole tool assembly comprising a sleeve member (24), a tube member (18) partially located within said sleeve member (24), a running tool sub-assembly (20) below the tube member (18) and a tubular extension member (22) depending from the running tool sub-assembly (20), characterized in that the external diameter (19) of the tube member (18) is equal to the external diameter of the tubular extension member (22).