GB2094853A - Releasable rotary drive coupling - Google Patents

Abstract

A releasable coupling for rotary drive with advance or reverse thrust, suitable for incorporation in a downhole drilling device to enable the latter to operate simultaneously as a casing advancer, with a drive engageable and disengageable blind and in accretable debris and dirt for removal of a drilling head leaving the casing in situ, comprises, preferably, a "bayonet"-like connection with sprung drive projections 8 and, for these, a locating shoulder and longitudinal and peripheral cam surfaces. The driving member 7 drives the drilling head and, through the coupling 5, 8, a front section of the casing with leading and trailing reaming teeth 22, 10, with a free rotary connection to the next casing section 3, 2. Reverse rotation releases the coupling. <IMAGE>

Description

SPECIFICATION Releasable rotary drive coupling The present invention relates to releasable rotary drive couplings and has particular -application to downhole shearers.

A downhole shearer is a device usually comprising a drilling head and a (usually much narrower) string of rods connected to the head to drive it and is usually employed to bore or widen holes in the ground, e.g. for geological exploration, or for well-drilling for oil, gas, water and so on. As the shearer advances into the hole, drilling is periodically interrupted and an extra length of rod added to the string.

A difficulty with known shearers is that the sides of the hole often tend to collapse in places (e.g. where the hole is bored through loose or liquid strata), sometimes before the shearer is withdrawn so that the shearer has to be used to bore its way out when withdrawn, and sometimes after withdrawal of the shearer so that there is difficulty in inserting a supporting liner (usually called a "casing") for the hole if the hole is to be retained. (Such a casing is usually in the form of a string of casing sections and may eventually be withdrawn, as when the hole is no longer required and is to be filled in.) A proposal has been made (though not yet communicated to the public) to overcome this difficulty by arranging for the casing to advance with the drilling head. Such a device may then be termed a "downhole casing advancer".According to the proposal, the front section of the casing string was intended to be in driven connection with the rod string just behind the drilling head and in a freely rotatable traction connection with the remainder of the casing string. This driving connection was intended to be by an inner member fixed at the head of the rod string to be driven thereby and in turn to drive the drilling head fixedly connected thereto and to drive the front section of the casing in order to withdraw the drilling head through the casing. Since this should enable a new drilling head to be substituted for the old one, the inner member was termed a "sub".In order to enable positive rotary drive coupled with substantial thrust for advancing the whole arrangement and coupled with substantial reverse thrust for withdrawing the casing string when no longer required, and yet provide the ability for the sub to be released from the casing string in situ when it was required to withdraw the drilling head (and rod string) without the casing string, the proposal described a very complicated ram system intended to be operable solely by movement of the rod string.

When the present inventors tried to put the proposal into effect, the practical difficulties that they found proved insurmountable. Some of these difficulties were that in the proposed downhole casing advancer the ram system had to be operated blind, i.e. when it was inaccessible (with the advancer in situ), both for connection and release between the sub and casing, the advancer had to be robust enough to stand up to the knocks and other stresses encountered under practical drilling conditions (and test standards relating thereto often specified by contractors), and the ram system had to be operable in a positive, consistent and repeatable manner in spite of the usual debris and dirt, and the tendency to resulting accretions thereof in its mechanism.

After many trials, the present inventors realised that a completely different releasable driving connection was essential and, after the expenditure of much time, effort and money, produced a releasable driving connection that would ameliorate the above difficulties. Although the connection was produced as part of the improvement of a downhole casing advancer, it is realised that it may have wider application.

Accordingly, the present invention provides a releasable rotary drive coupling comprising first and second members between which drive is to be exerted, in which coupling said members comprise respective abutment means for co-operation with each other (together forming what is hereinafter referred to as a "set") and each comprising first and second portions, the respective first portions being engageable together upon rotation in one sense of one of said members relative to the other to provide a connection for rotary drive with longitudinal thrust between said members and disengageable therefrom by rotation in the opposite sense, and the respective second portions being engageable together upon rotation in said one sense of said one member relative to the other to provide a connection for rotary drive with opposite longitudinal thrust between said members and disengageable therefrom by rotation in said opposite sense, whereby the connections can be engaged and disengaged without access to the coupling.

Although a certain amount of play may be allowed between the position for engagement between said first portions and that for said second portions, this will allow accretion of dirt etc., and the effects of this can be substantially reduced if said first portions and said second portions are arranged for simultaneous engagement and simultaneous disengagement.

A particular form of embodiment which allows easy and simple engagement and disenyagement with very definite action and firm driving characteristics is one in which the abutment means of a first one of said members has wall portions that define a circumferentially extending slot closed at one end and open at the other end, and the abutment means of the second one of said members comprises a protuberance to enter said slot by way of its open end, said protuberance and said wall portions providing said first and second portions.

Further to reduce the effects of accreted dirt, said protuberance is provided by a retractable ram.

This action is further helped if the ram is spring biased towards its protuberant position. The accretion of dirt can be made of even less effect if said first member has a circumferential cam surface so directed as to allow the ram to protrude further as it traverses said slot towards said closed end.

If it is necessary to move one of the members past the other, the ram can be made fully retractable into said second member, to effect which said first member has a longitudinally deepening cam surface serving also to allow the ram to protrude further as it approaches said slot, both movements of the cam thereby being aided against accreted dirt.

To aid blind engagement of the coupling, one of said members has a circumferentially extending shoulder to co-operate with a part of the other member to limit relative longitudinal movement therebetween. This enables e.g. one of said members to be dropped past the other until arrested by the shoulder which is preferably provided on said first member, when said second member is the dropping one and may thus be required to be lighter. If said shoulder is continuous with a said wall portion, manufacture is easier as also is the rotary engaging movement.

A particularly simple embodiment is obtained if said part is provided by said ram.

The movements for engagement and disengagement are much simplified if at least part of one of said members (hereinafter referred to as an "inner member") is rotatable as aforesaid within at least part of the other member (hereinafter referred to as an "outer member"), such partscomprising said abutment means. Of the possible arrangements thereof, the simplest and most convenient form is when said outer member is said first member and said inner member is said second member.

For ease of manufacture, at least part of the abutment means of said first member is provided by an insert welded into position in said first member. Manufacture is further simplified if said insert is welded into an opening through said first member so as to close said opening. This helps to reduce loss of slurry, as also does providing said ram in a blind hole in said second member.

Manufacture is further simplified if said inner member is formed as a single piece of material apart from the abutment means.

There may be provided a plurality of said sets of the abutment means to help reduce the driving and thrust stresses involved, which may further be helped if the sets are at the same longitudinal position and circumferentially spaced apart, e.g.

symmetrically around the longitudinal axis. For a small coupling, e.g. of outside diameter about 6 cm, two sets may be used, and three or more for large coupiings if necessary.

As explained above, the coupling was developed for use in a downhole casing advancer.

For this purpose, the inner member is a sub for attachment to a rod string to drive a drilling head and the outer member is a casing lead section. To aid penetration of the ground by the advancer, the outer member has cutting teeth at its leading edge so that it acts as a reamer and, to aid withdrawal of the advancer, the outer member has cutting teeth at its trailing edge. In order to avoid the need to rotate the remainder of the casing with the lead section, the latter has a rotary thrust bearing connection to the next casing section. In order to withstand the rigorous conditions likely to be encountered, the rotary thrust bearing connection preferably comprises a phosphor-bronze bearing element.

With the conditions appertaining to an advancer, it has been found that the optimum slope of the longitudinally deepening cam surface is about 5".

Reference will now be made by way of example to the accompanying drawings in which: Fig. 1 is a half longitudinal section of the leading and next sections of casing of an advancer embodying the invention; Figs. 2-6 are more detailed sections of the respective parts of Fig. 1; Figs. 5AD are views of details appertaining to Fig. 5; and Figs. 7 and 8 are a plan and part cross-sectional view of a sub of the embodiment.

Referring to the drawings, 2 and Fig. 2 are a casing crossover coupling. 3 and Fig. 3 are a stationary casing, the aforesaid next section. 4 and Fig. 4 refer to a reaming cap having trailing cutting teeth 10 and bearing via a seal 12 and L-bearing 14 of phosphor-bronze against section 3. 5 and Fig. 5 refer to the main casing body constituting the aforesaid leading section and welded at 1 6 to cap 4. Fig. 5A is a view of the welding edges of a hole in section 5 into which is welded an insert 18 shown in perspective in Fig. 5D for drive in the direction of arrow 20. 6 and Fig. 6 refer to a casing shoe screwed to section 5 and carrying leading reaming teeth 22.

The embodiment comprises a sub 7 mounting a ram 8 and cut flat at 9 and 11 to allow the passage there-past of slurry which enters the drilling head cavity through a bore 13 in sub 7.

Ram 8 is retained by ring 1 5 with seal 1 7 against the action of spring 19.

A releasable rotary drive coupling comprises first (2, 3, 4, 5, 6) and second (7, 8) members between which drive is to be exerted, in which coupling said members comprise respective abutment means (18, 21) for co-operation with each other (together forming what is hereinafter referred to as a "set") and each comprising first (21, 23, 24) and second (24, 25, 26) portions, the respective first portions being engageable together upon rotation in one sense of one of said members relative to the other to provide a connection for rotary drive with longitudinal thrust between said members and disengageable therefrom by rotation in the opposite sense, and the respective second portions being engageable together upon rotation in said one sense of said one member relative to the other to provide a connection for rotary drive with opposite longitudinal thrust between said members and disengageable therefrom by rotation in said opposite sense, whereby the connections can be engaged and disengaged without access to the coupling.

Said first portions and said second portions are arranged for simultaneous engagement and simultaneous disengagement.

The abutment means of a first one of said members has wall portions (21, 24, 26) that define a circumferentially extending slot closed at one end (24) and open at the other end, and the abutment means of the second one of said members comprise a protuberance (8) to enter said slot by way of its open end, said protuberance and said wall portions providing said first and second portions.

Said protuberance is provided by a retractable ram.

The ram is spring-biased towards its protuberant position.

Said first member has a circumferential cam surface (27) so directed as to allow the ram to protrude further as it traverses said slot towards said closed end.

Said first member has a longitudinally deepening cam surface (28) to allow the ram to protrude further as it approaches said slot.

One of said members has a circumferentially extending shoulder (21) to co-operate with a part (23) of the other member to limit relative longitudinal movement therebetween.

Said shoulder is provided on said first member.

Said shoulder (21) is continuous with a said wall portion (24). (See Fig. 5C.) Said part is provided by said ram.

At least part of one of said members (hereinafter referred to as an "inner member") is rotatable as aforesaid within at least part of the other member (hereinafter referred to as an "outer member"), such parts comprising said abutment means.

Said outer member is said first member and said inner member is said second member.

At least part of the abutment means of said first member is provided by an insert (18) welded into position in said first member.

Said insert is welded into an opening (29) through said first member so as to close said opening.

Said ram is provided in a blind hole in said second member.

Said inner member is formed as a single piece of material apart from the abutment means.

There is a plurality of said sets of the abutment means.

The sets are at the same longitudinal position and circumferentially spaced apart.

A downhole casing advancer comprises the coupling.

The inner member is a sub to drive a drilling head (not shown) and the outer member is a casing lead section.

The outer member has cutting teeth (22) at its leading edge.

The outer member has cutting teeth (10) at its trailing edge.

The outer member has a rotary thrust bearing connection (14) to the next casing section (3, 2).

Said rotary thrust bearing connection comprises a phosphor-bronze bearing element (14).

The longitudinally deepening cam surface has a slope of about 5 .

Essentially, the advancer tows down its own non-rotating casing to line a well hole to within six inches of the drill bit. This virtually eliminates the loss of costly circulation mud usually experienced when drilling through porous formations. It also gives a high degree of protection against cave-ins and squeezes which occur frequently during breaks in conventional drilling operations.

The decision to embark on the design of this unique down-hole accessory was inspired by the realisation that literally millions of pounds worth of circulations muds are lost every year in oil, gas and coal drilling operations and that further massive sums are spent in re-drilling after cave-ins and in cementing standard casing strings.

The casing advancer is made in two parts: an inner activator sub to which the drill string passes, and an outer casing that acts as a reamer.

The activator sub has a rotary connection at its upper end which is attached to the drill string; a second rotary connection at the base is mated with the drill bit. On opposing sides and some two thirds of the way down this sub, a pair of spring loaded latches are set into the walls and protected by scraper rings. The dimensions of these latch ports are highly critical, in that they must prevent excess lateral movement of the latches yet allow free engagement and retraction even under the conditions of intense frictional heat encountered in drilling. The tolerance is fixed at 0.001 5" and the high grade steel is mirror finished.

While the "east-west" external diameter of the sub is machined as a tapered fit to the i.D. of its outer casing, the "north-south" diameter is reduced to allow for the passage of circulation mud. The outer casing is machined internally to provide a "shoulder" upon which the sub is located, and immediately above that is a pair of blocks, each with a female bayonet fitting machined into the inner profile. Thus, when the sub is pressed home and rotated through 90 degrees, the latches are engaged and rotational power is transmitted from the drill to the lower and larger dimensioned section of the casing advancer. The upper, non-rotating section is separated from that lower, moving part by a bearing and screwed and welded to the casing string which it tows down the hole.

To provide a tolerant path for the casing string, the diameter of the advancer is fractionally greater than that of the string and its shoulders are fitted with tungsten carbide inserts to improve its reaming action.

To prevent the activator latches being "bounced" out of connection by a sudden shock to the drill bit or to the reamer, accommodation space has been provided on the inner profiles of the bayonet fittings. This is sufficient to allow the drill to "bounce" through 200 before the advancer is dis-engaged; enough to cope with minor torsionai stresses, not so great a restriction as to jeopardise the drill strings.

The inventors have undertaken a number of successful field trials with the new tool and are satisfied that it can effect considerable savings in materials and time for oil, gas and coal drilling operations and in geophysical research.

Further, while the design is complex and calls for extremely fine engineering tolerances, they are satisfied that it can be "up-sized" to provide ventilation and access shafts for such applications as mining rescue work.

Because of the virtually non-existent machining tolerances and mirror finish required on certain of the interior profiles, aliied to the need for high product reliability, the advancer is fashioned from SKF 326, a special carbon steel of oilfield grade which is of outstanding machinability and, with a tensile strength of 125 ksi allied to a yield strength of 110-140 ksi, of more than adequate strength for even this rigorous down-hole application.

Because it is made by the Swedish SKF-MR process, the steel is also extremely clean and less prone to fatigue than conventionally made metals.

It also displays good resistance to attack by sour gas.

Claims (1)

1. A releasable rotary drive coupling comprising first and second members between which drive is to be exerted, in which coupling said members comprise respective abutment means for cooperation with each other (together forming what is hereinafter referred to as a "set") and each comprising first and second portidns, the respective first portions being engageable together upon rotation in one sense of one of said members relative to the other to provide a connection for rotary drive with longitudinal thrust between said members and disengageable therefrom by rotation in the opposite sense, and the respective second portions being engageable together upon rotation in said one sense of said one member relative to the other to provide a connection for rotary drive with opposite longitudinal thrust between said members and disengageable therefrom by rotation in said opposite sense, whereby the connections can be engaged and disengaged without access to the coupling.

2. A coupling as claimed in claim 1, in which said first portions and said second portions are arranged for simultaneous engagement and simultaneous disengagement.

3. A coupling as claimed in claim 1 or 2, in which the abutment means of a first one of said members has wall portions that define a circumferentially extending slot closed at one end and open at the other end, and the abutment means of the second one of said members comprise a protuberance to enter said slot by way of its open end, said protuberance and said wall portions providing said first and second portions.

4. A coupling as claimed in claim 3, in which said protuberance is provided by a retractable ram.

5. A coupling as claimed in claim 4, in which the ram is spring-biased towards its protuberant position.

6. A coupling as claimed in claim 4 or 5, in which said first member has a circumferential cam surface so directed as to allow the ram to protrude further as it traverses said slot towards said closed end.

7. A coupling as claimed in claim 4, 5 or 6, in which said first member has a longitudinally deepening cam surface to allow the ram to protrude further as it approaches said slot.

8. A coupling as claimed in any preceding claim, in which one of said members has a circu mferentially extending shoulder to co-operate with a part of the other member to limit relative longitudinal movement therebetween.

9. A coupling as claimed in claim 8 when appendant to claim 3, in which said shoulder is provided on said first member.

10. A coupling as claimed in claim 9, in which said shoulder is continuous with a said waU portion.

1 A coupling as claimed in claim 9 or 10 when appendant to claim 4, in which said part is provided by said ram.

1 2. A coupling as claimed in any preceding claim, in which at least part of one of said members (hereinafter referred to as an "inner member") is rotatable as aforesaid within at least part of the other member (hereinafter referred to as an "outer member"), such parts comprising said abutment means.

13. A coupling as claimed in claim 12 when appendant to claim 3, in which said outer member is said first member and said inner member is said second member.

14. A coupling as claimed in claim 13, in which at least part of the abutment means of said first member is provided by an insert welded into position in said first member.

1 5. A coupling as claimed in claim 14, in which said insert is welded into an opening through said first member so as to close said opening.

1 6. A coupling as claimed in claim 13, 14 or 1 5, when appendant to claim 4, in which said ram is provided in a blind hole in said second member.

17. A coupling as claimed in claim 13, 14, 1 5 or 16, in which said inner member is formed as a single piece of material apart from the abutment means.

18. A coupling as claimed in any preceding claim, in which there is a plurality of said sets of the abutment means.

19. A coupling as claimed in claim 18, in which the sets are at the same longitudinal position and circumferentially spaced apart.

20. A coupling substantially according to any embodiment hereinbefore described.

21. A coupling substantially according to any embodiment hereinbefore described with reference to and illustrated in the accompanying drawings.

22. A downhole casing advancer comprising a coupling as claimed in any preceding claim.

23. An advancer as claimed in claim 22 when appendant to claim 13, in which the inner member is a sub to drive a drilling head and the outer member is a casing lead section.

24. An advancer as claimed in claim 23, in which the outer member has cutting teeth at its leading edge.

25. An advancer as claimed in claim 24, in which the outer member has cutting teeth at its trailing edge.

26. An advancer as claimed in claim 23 or 24, in which the outer member has a rotary thrust bearing connection to the next casing section.

27. An advancer as claimed in claim 26, in which said rotary thrust bearing connection comprises a phosphor-bronze bearing element.

28. An advancer as claimed in any one of claims 23 to 27, when appendant to claim 7, in which the longitudinally deepening cam surface has a slope of about 5 .

29. A downhole casing advancer substantially according to any embodiment hereinbefore described.

30. A downhole casing advancer substantially according to any embodiment hereinbefore described with reference to and illustrated in the accompanying drawings.