GB2178093A - Releasable spear for retrieving a hollow member from a well bore - Google Patents

Abstract

A releasable spear for retrieving a hollow member from a well bore has a top tubular member (1) connected to a tubular mandrel (2) which in turn is connected to a tubular lower mandrel (3), and rotatably disposed about the member (2) is a tubular sleeve (4). The sleeve (4) carries a rotatable and slidable grapple carrier (5). The grapple carrier has a body (51) which is provided with L-shaped limbs (52) each having a leg (53) and foot (54), the part of the leg (53) remote from the foot being connected to the body by pivot pin (55). Each foot has a tapered heel (55) arranged to be located in and to mate with a respective wedge-shaped slot (44) disposed in the sleeve (4). Each foot has a toe formed by a grapple segment (56) for engaging the hollow member to be retrieved. Each limb is biassed radially outwardly by compression springs (62) and the radial extent of movement of the limbs is governed by aperture (60) and pin (61). The spear of the invention enables the grapple segments (56) to collapse and pass through bore restrictions and to subsequently move through a greater radial extent than hitherto. <IMAGE>

Description

SPECIFICATION Releasable spear for retrieving a hollow member from a well bore This invention relates to a releasable spear for retrieving a hollow member such as a pipe from a well bore and in particular, although not exclusively, the invention has particular relevance to retrieval of pipes located in the sea.

A known spear has a radially expandable cutter connected to one end thereof, at the end of the spear remote from the cutter is provided a radially expandable grapple and positioned on the remote side of the grapple from the cutter is a marine swivel having a relatively large diameter compared with the cutter. In operation the spear is connected to a drilling string and lowered into a pipe to be retrieved so that the cutter and the grapple locate inside the pipe to be retrieved and the swivel rests upon the top outer circumferential surface of the pipe thereby taking the weight of the spear so that the drilling string tension created by the weight of the spear is released. The cutter is radially expanded by pumping fluid through a hollow internal bore of the spear. The spear is then rotated hence rotating the cutter to sever the pipe.Because operation upon the pipe necessarily takes place with the drilling string relaxed, it is necessary for there to be provided a marine swivel for location upon the top of the pipe which acts as a bearing surface for rotation of the cutter, for the drilling tools above the cutter to be made from very heavy duty materials and to be rigid to avoid damage to the cutting tool. After the cutting tool has severed the pipe the cutter is raised and due to cooperating tapers, so the grapple is radially expanded and the severed part of the pipe is then brought to the surface by again tensioning the drilling string.

In the applicants copending British Patent Application No. 8505200 there is provided a releasable spear which is in tension at all times so that the cutting operation is simplified. In accordance with the applicants' said copending application there is provided a releasable spear for retrieving tubular members from a well bore including a series connection of first, second and third tubular members in which the internal passageway of the three members intercommunicate with one another and extend to the end of the third member remote from the second member which said end is adapted for connection of a utilisation means, a further member which is slidably and rotatably disposed about the second member, said further member having a securing means disposed circumferentially thereabout, cooperating means on the first member and the further member for bringing the securing means into frictional engagement with a tubular member to be retrieved, whereby, in operation, the spear is connected to a drilling string and the securing means is lowered into the tubular member to be retrieved, the cooperating means is actuated to bring the securing means into frictional engagement with the tubular member to grip the inside thereof, and the first, second and third members are rotated to drive the utilisation means whilst the drilling string remains substantially under tension.

Although the invention described in GB Patent Application 8505200 has proved to have considerable advantages over the above described prior art it has been found that a onepiece grapple carrier as disclosed for the securing means in the said application was inflexible and caused fractures at the joint between the grapple carrier and the grapple arms carrying the grapples, so that the complete grapple carrier to be scrapped. It should here be understood however, that the scope of the invention defined in the said GB Patent Application No. 8505200 is not limited to the use of a one-piece grapple carrier and the sufficiency and utility of the invention disclosed in the applicants' said copending application is not dependent upon such a grapple carrier.

The present invention seeks to provide a releasable spear which may or may not be in tension at all times during the cutting operation in which the expense associated with having to scrap the completed grapple carrier is substantially mitigated in the event that a grapple arm should fracture and moreover in which the grapple securing means is able to pass through restrictions in the bore of a hollow member to be retrieved.

According to this invention there is provided a releasable spear for retrieving a hollow member from a well bore including a tubular member arranged to be connected to a drill string and a securing means disposed around the circumference of the tubular member, said securing means having a body longitudinally slidably arranged along the tubular member and, connected to the body, a plurality of individual circumferentially spaced radially extending limbs for gripping the inside of the hollow member to be retrieved, each said limb being arranged to slide along a taper on said tubular member such that relative longitudinal movement between the tubular member and securing means causes the limbs to radially expand.

Preferably the limbs are each formed by an L-shaped member having a leg and a foot, the top of the leg being pivotally connected to the body and foot having the heel thereof arranged to slide along said taper with the toe portion thereof being arranged to grip the inside of the tubular member to be retrieved.

Preferably a discrete longitudinal taper is provided for each L-shaped member and conveniently each taper is recessed below the external periphery of said tubular member and each said heel is supported in a respective tapered recess. Preferably each toe portion of the foot has a bevelled leading and trailing edge to ease insertion into and retrieval from the hollow member to be retrieved.

Advantageously each limb is biassed radially outwardly from the body, conveniently by at least one spring secured to the body and which spring acts upon a radially inner side of said leg.

Preferably limit means are provided for limiting the radial movement of each said limb and convenientiy said limit means comprise an aperture in said leg and a fixed pin on the body, said pin extending through the aperture, the size of said aperture in relation to the pin determining the limb radial movement. Advantageously, the tubular member has a radially enlarged end portion arranged to act as a lower end stop of the slidable movement of the securing means.

In a currently preferred embodiment the tubular member is rotatably disposed with respect to and about a middle tubular member which is connected at opposing ends thereof to a top and a lower tubular member respectively, there being provided an interconnecting internal passage through the top, middle and lower tubular member. Advantageously, a utilisation means, such as a cutter, is provided on an end of the lower tubular member remote from the middle tubular member. In the said embodiment preferably a dog clutch connection is provided between the top tubular member and said tubular member.

The invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 shows a longitudinal partial crosssection of a releasable spear in accordance with this invention, Figure 2 shows a view along arrow headed lines 2-2 of Fig. 1, and Figure 3 shows a view along arrow headed lines 3-3 of Fig. 1.

In the Figures like reference numerals denote like parts.

The releasable spear shown in Fig. 1 has a top tubular member 1 connected to a tubular mandrel 2 which in turn is connected to a tubular lower member 3, and rotatably disposed about the member 2 is a tubular sleeve 4. The member 1 has a longitudinal bore 10 and a lower portion 13 of the member 1 has an enlarged diameter, the lower face of the portion 13 being provided with tapered screw thread 14. The screw thread 14 is arranged to cooperate with a mating screw thread on end 21 of the mandrel 2. The lower (in operation) external surface of the portion 13 is provided with one part 80 of a dog clutch.

The mandrel 2 has a longitudinal internal bore 22 for intercommunicating with the bore 10 and a shoulder 23 on the mandrel 2 is arranged to abut a recessed surface 15 of the top member 1. The lower end of the mandrel 2 is provided with a tapered external screw thread 24 which is arranged to mate with a cooperating internal screw thread depending from an upper bore 31 in the lower member 3.

The mandrel 2 has a lower shoulder 25 abutting against an internal abutment 32 on the lower member 3.

The lower member 3 has an upper portion 33 of enlarged diameter and a lower portion 34 of reduced diameter, the lower end of the portion 34 being provided with an externally tapered screw thread 35 for connection to a utilisation means which may be, for example, a radially expandable cutter (not shown). The member 3 has a longitudinal internal bore 36 of circular cross-section which communicates with the 22 so that the bores 10, 22 and 36 all intercommunicate.

The sleeve 4 is mounted on the mandrel 2 for rotational movement through the intermediary of an upper bush 41 and a lower bush 42. Each of the bushes may be made from a suitable material selected in dependence upon the environment in which the spear is to be used but the material may be, for example, brass or ceramic. At the lower end (in operation) of the sleeve 4 there is provided an enlarged radial portion 43, the lower surface of which rotatably abuts an upper surface of the portion 33 through the intermediary of a thrust bearing 70. The enlarged radial portion 43 is generally of circular cross-section but 6 equi-circumferentially spaced, recessed, wedge shaped slots 44 longitudinally extend in the portion 43 with the greatest depth being at the top (in operation) of the portion 43. The slots 44 each accommodate a grapple segment as will now be described.

The grapple carrier 5 has a body 51 the top end of which is shaped to form the other part 81 of the dog clutch and the body 51 is arranged to abut the enlarged radial portion 43 which thus acts as a lower limit of travel for the grapple carrier. The body 51 is provided with 6 equi-circumferentially spaced individual L-shaped limbs 52 each having a leg 53 and a foot 54, the part of the leg 53 remote from the foot being connected to the body 51 by a pivot pin 55. Each foot 54 has a tapered heel 55 arranged to be located in and to mate with a respective slot 44. Each foot also has a toe formed by a grapple segment 56 which is secured to a respective heel 5 by bolts (not shown). A leading and a trailing edge 57, 58 respectively, of each segment 56 is bevelled to ease insertion into and retrieval from a pipe to be retrieved.

A radially inner side 59 of each leg 53 is undercut and the lower end thereof is formed to provide a semi-circularly shaped aperture 60 which cooperates with a pin 61 inserted into the body 51 so that radial movement of the limb 52 is limited thereby, the size of the aperture in relation to the pin determining the radial movement of limb 52. For each limb 52 there is provided three radially extending coil compression actuating springs 62, the springs being longitudinally disposed with respect to one another. The springs 62 are each located in a respective blind bore in the body 51 and arranged to abut the underside of the radially inner side 59 undercut surface so that the arm 52 associated herewith is biassed radially outwardly.

The part of the dog 80 shown in Fig. 2 has two radially enlarged portions 82 each extending through an arc of 100" with two reduced radius portion 83 each extending through 80 .

The part 81 of the dog clutch shown in Fig. 3 is complementarily shaped to the part so that rotation of the top tubular member 1 in a clockwise direction engages the clutch with parts of portions 82 underlying increased radially enlarged portions 84 until limited after 15 of engagement stops 85.

In operation, with a utilisation means such as a cutter connected to the screw thread 35 and with the top tubular member 1 engaged with the grapple carrier 5 by the dog clutch, so the spear in connected to a drilling string (not shown) and lowered into a pipe to be retrieved. The springs 62 act to bias the associated segments 56 radially outwardly and so when the segments contact with a pipe to be retrieved downward movement of the drilling string enables the bevelled edges 57 to abut against the top edges of the pipe to be retrieved thereby forcing the segments 56 radially inwardly into the pipe to be retrieved against the force of springs 62.When the cutter has reached the required point within the pipe to be retrieved then the top member 1 is rotated counter clockwise to release the grapple carrier 5 and an upward movement of the drilling enables each heel 55 to move longitudinally along its associated slot 44 under gravitational force and such movement forces the segments 56 into tight frictional engagement with the inside of the pipe to be retrieved. The drilling string is then rotated in a clockwise direction to effect cutting of the pipe and such cutting operation is normally performed whilst the drilling string is in tension. When the pipe has been cut, further upward movement of the drilling string withdraws the cut section of the pipe.

It will therefore be seen that the cutting and retrieving operation may be effected while the drilling string is solely in tension.

The present invention has the advantage that the grapple segments are mounted independently of one another via compression springs 62 which enable the segments to collapse through bore restrictions and the arrangement of the present invention enables the segments 56 to move through a greater radial extent than hitherto. Moreover, any damaged segments may be individually replaced. The embodiment herein described also has the advantage that a larger than normal diameter top tubular member may be used which provides greater stability during a cutting operation.

Claims (14)

1. A releasable spear for retrieving a hollow member from a well bore including a tubular member arranged to be connected to a drill string and a securing means disposed around the circumference of the tubular member, said securing means having a body longitudinally slidably arranged along the tubular member and, connected to the body, a plurality of individual circumferentially spaced radially extending limbs for gripping the inside of the hollow member to be retrieved, each said limb being arranged to slide along a taper on said tubular member such that relative longitudinal movement between the tubular member and securing means causes the limbs to radially expand.

2. A releasable spear as claimed in claim 1, wherein the limbs are each formed by an Lshaped member having a leg and a foot, the top of the leg being pivotally connected to the body and the foot having the heel thereof arranged to slide along said taper with the toe portion thereof being arranged to grip the inside of the tubular member to be retrieved.

3. A releasable spear as claimed in claim 2, wherein a discrete longitudinal taper is provided for each L-shaped member.

4. A releasable spear as claimed in claim 3, wherein each taper is recessed below the external periphery of said tubular member and each said heel is supported in a respective tapered recess.

5. A releasable spear as claimed in claim 4, wherein each toe portion of the foot has a bevelled leading and trailing edge to ease insertion into and retrieval from the hollow member to be retrieved.

6. A releasable spear as claimed in any preceding claim, wherein each limb is biassed radially outwardly from the body.

7. A releasable spear as claimed in claim 6, wherein the biassing is performed by at least one spring secured to the body and which spring acts upon a radially inner side of said leg.

8. A releasable spear as claimed in claim 2, wherein limit means are provided for limiting the radial movement of each said limb.

9. A releasable spear as claimed in claim 8, wherein said limit means comprise an aperture in said leg and a fixed pin on the body, said pin extending through the aperture, the size of said aperture in relation to the pin determining the limb radial movement.

10. A releasable spear as claimed in any preceding claim, wherein the tubular member has a radially enlarged end portion arranged to act as a lower end stop of the slidable move ment of the securing means.

11. A releasable spear as claimed in any preceding claim, wherein the tubular member is rotatably disposed with respect to and about a middle tubular member which is connected at opposing ends thereof to a top and a lower tubular member respectively, there being provided an interconnecting internal passage through the top, middle and lower tubular member.

12. A reieasable spear as claimed in claim 11, wherein a utilisation means is provided on an end of the lower tubular member remote from the middle tubular member.

13. A releasable spear as claimed in claim 10 or 11, wherein a dog clutch connection is provided between the top tubular member and said tubular member.

14. A releasable spear substantially as herein described with reference to and as shown in the accompanying drawings.