GB2256884A - Tubular fitting for use in a drilling string - Google Patents

Abstract

A tubular fitting 10 is positioned above a drilling tool coupled with a drill string where in use an increase in fluid pressure acts on the head seal 25 to move the sleeve 16 downwardly so that tail seal 29 seals on sleeve seal 30. When the fluid pressure decreases the spring 26 returns the head seal 25 and sleeve 16 to the upper 'valve open' position allowing mud or drilling fluid to drain out through the ports 28. The apparatus thus operates as a dump valve. The movement of sleeve 16 may also be used to operate a locking mechanism (41) to lock or unlock a tool under differential fluid pressure action. <IMAGE>

Description

TUBULAR FITTING FOR USE IN A DRILLING STRING This invention relates to a tubular fitting for use in a drilling string.

During normal and directional drilling operations e.g.

for oil and / or gas. drilling fluid or "mud" is used for a number of reasons. one of which is in order to carry rock cuttings out of the hole being drilled to the surface.

When the usual drilling string is pulled out of the hole, it is often the case that this fluid is unable to drain away from the pipe being pulled. Thus, there are often small openings at the bottom of the pipe around the drill bit that restrict the flow of fluid (mud) out of the pipe. In addition. there are different drilling tools used in some circumstances which also effect the draining out of the pipe e.g. core barrels, mud motors and mud tools.

The present invention has therefore been developed primarily with a view to improve drainage from a pipe located above a drilling or working tool, but in such a way as not to interfere with or adversely affect regular drilling operations.

In one aspect, the invention provides for improved drainage from the pipe while it is being pulled out of a hole, which improves working conditions on a rig floor, involves less waste of mud, and less time to wait for the pipe to drain and also less pollution when drilling offshore.

In a further aspect, the invention provides an improved locking mechanism in a drill string to lock a tool in position.

Accordingly, in a first aspect of the invention, there is provided a tubular fitting for use in a drill string to be positioned above a working or drilling tool coupled with the drill string, said fitting comprising: a cylindrical housing having an inlet at its upper end for admitting drilling fluid or "mud", and an outlet at its lower end for discharging the drilling fluid; a sleeve mounted for axial slidable movement within the housing between upper and lower positions, and defining a through-flow passage communicating with said inlet and with said outlet; an annular chamber defined between the inner wall of the housing and the outer wall of the sleeve; inlet means in the wall of the housing for communicating the usual annular pressure surrounding the drill string in service with said annular chamber;; a head seal provided at the upper end of the sleeve and arranged to have its upper face exposed to the pressure prevailing at the inlet in order to exert a downward force on the sleeve, and its lower face exposed to the pressure prevailing in said annular chamber to exert an upward force on the sleeve; biasing means for applying an additional upward force to the head seal; a dump chamber at the lower end of the housing; a discharge outlet in the wall of the housing near the lower end thereof and communicable with said dump chamber; and, a tail seal provided at the lower end of the sleeve and movable upwardly and downwardly with the sleeve depending upon the direction of the net force acting upon the head seal, said tail seal closing access to said discharge outlet when the sleeve is in the lower position whereby fluid supplied to the inlet can pass straight through the fitting, and said tail seal allowing access to the discharge outlet when the sleeve is in the upper position whereby fluid in the fitting can be discharged via the dump chamber and the discharge outlet.

Therefore, a tubular fitting according to this one aspect of the invention can deliver a pumped supply of fluid to the working tool when the supply pressure exerts a sufficient downward force on the head seal to overcome the combined upward force acting on the head seal, so that regular drilling operations can be carried out. However, if the supply pressure falls, or during withdrawal of the pipe string, there will be a net upward force acting on the head seal so that the sleeve takes-up the upper position and then readily allows fluid to be discharged via the passage in the sleeve, the dump chamber and the discharge outlet.

Preferably. the biasing means takes the form of a compression spring housed within the annular chamber, and acting directly on the underside of the head seal.

In a preferred arrangement, an annular floating piston is slidable within the annular chamber which it subdivides into an upper chamber and a lower chamber, and with the lower chamber communicating with said inlet means which admits annular pressure to the fitting.

An internal balancing or transfer port may be provided in the wall of the sleeve, close to the tail seal, and preferably a seal ring surrounds the sleeve and is located by the housing at a position above the port and below the inlet means so that a chamber defined below the seal can receive pumped fluid pressure from the sleeve to exert an upward force on the seal, in opposition to a downward force exerted on the seal ring by a second chamber above the seal ring which communicates with the inlet means. The seal ring therefore functions to hold or seal the pressure differential between pump or drill string pressure (the pumped pressure in the sleeve) and the annular pressure (in the annular space surrounding the drill string).

The tubular fitting defined above, and its preferred aspects, comprises a type of "dump valve" fitting which can be operated to discharge drilling fluid or mud during withdrawal.

In a further aspect of the invention, the tubular fitting is modified so as to function as a fluid pressure operated locking mechanism for a tool in a drill string.

In this further aspect of the invention, the discharge outlet is omitted, and a locking sleeve is coupled with the lower end of the sleeve of the fitting (referred to hereinafter as the main sleeve), and is movable up and down with the main sleeve as a consequencefl of variation in the differential pressure action on the head seal. Locking fingers are coupled with the locking sleeve and when the tool is activated the locking fingers are locked in position, but when the tool is deactivated, the locking sleeve is pushed back off the fingers allowing them to move freely, thereby unlocking the mechanism.

Embodiments of the invention will now be described in detail, by way of example only. with reference to the accompanying drawings, in which: Figure 1 is a longitudinal sectional view of a first embodiment of tubular fitting according to the invention, for use in a drill string. and in a first mode of operation suitable for discharging or "dumping" drilling fluid or "mud"; Figure 2 is a view, similar to Figure 1, illustrating the fitting in an alternative operating mode, in which drilling fluid supplied to the fitting can pass downwardly straight through the fitting and further along the drill string to the drilling or working tool; Figure 3 is a view, similar to Figure 1, showing an alternative embodiment which is modified relative to the embodiment of Figures 1 and 2; Figure 4 is a view of the alternative embodiment, and corresponding with Figure 2; and, Figure 5 is a view, similar to Figures 1 to 4, showing a further modification of the tubular fitting to provide an embodiment of fluid pressure operated locking mechanism for a tool in a drill string in a further aspect of the invention.

Referring first to Figures 1 and 2 of the drawings, a first embodiment of tubular fitting according to the invention is designated generally by reference 10, and is intended to be coupled-up in a drill string via an upper tool joint 11 and a lower tool joint 12, with a working or drilling tool being coupled in the drill string below the fitting 10.

The tubular fitting 10 comprises a cylindrical housing 13 having an inlet 14 at its upper end for admitting drilling fluid or "mud", and an outlet 15 at its lower end for discharging the drilling fluid when the fitting is operating in a through-flow mode as shown in Figure 2, suitable for normal and directional drilling operations.

A sleeve 16 in the form of a mandrel is mounted in the housing 13 for axial slidable movement between an upper position shown in Figure 1 and a lower position shown in Figure 2. The tubular fitting 10 shown in Figures 1 and 2 effectively comprises a "dump valve", and is shown in the open position in Figure 1 and in the closed position in Figure 2. The sleeve 16 defines a through-flow passage 17 which communicates with the inlet 14 in order to receive a pumped supply of drilling fluid. and also with the outlet 15 in order to discharge the pumped flow of fluid when the dump valve is in the closed position shown in Figure 2.

An annular chamber 18 is defined between the inner wall of the housing 13 and the outer wall of the sleeve 16, and inlet means in the form of mud communication port 19 formed in the wall of the housing 13 communicates the usual annular pressure which will surround the drill string in service with the annular chamber 18. This takes place in indirect manner in the embodiment shown in Figures 1 and 2, via an external pressure chamber 20, floating piston 21 and oil chamber 22.

Upward flow check valve 23 and downward flow check valve 24 control fluid pressure flow between annular chamber 18 and oil chamber 22.

A head seal 25 is provided at the upper end of the sleeve 16, and is arranged to have its upper face exposed to the pressure prevailing at the inlet 14 in order to exert a downward force on the sleeve, and has its lower face exposed to the pressure prevailing in the annular chamber 18 which exerts an upward force on the sleeve. In addition, biasing means in the form of a compression spring 26 housed within annular chamber 18 applies an additional upward force to the head seal 25. Depending upon the direction of the net force applied to the head seal 25, the sleeve 16 will move upwardly or downwardly between the two positions shown in Figures 1 and 2.

A dump chamber 27 is arranged at the lower end of the housing 13, and a discharge outlet in the form of discharge flow ports 28 in the wall of the housing 13 near the lower end thereof are communicable with the dump chamber 27 when the sleeve 16 is in the upper position shown in Figure 1 i.e.

the open position of the dump valve.

A tail seal 29 is provided at the lower end of the sleeve 16, and is movable upwardly and downwardly with the sleeve. depending upon the direction of the net force acting upon the head seal 25. Thus. when the sleeve 16 is in the lower position shown in Figure 2, the tail seal 29 makes sealing engagement with sealing sleeve seals 30 provided at the lower end of the housing 13, whereby communication between the interior passage 17 of sleeve 16 with dump chamber 27 is closed, thereby closing access to the discharge outlet ports 28. Therefore, in the lower position shown in Figure 2, which is the closed position of the dump valve, pumped fluid supplied to the inlet 14 passes straight through the fitting 10 and exits via outlet 15.

The sleeve 16 will take-up the lower position shown in Figure 2, when the pumped fluid supply pressure to the inlet 14 is sufficient to exert a greater downward force on head seal 25, than the upward force exerted on head seal 25 by the pressure prevailing in annular chamber 18 and the upward biasing force of the spring 26. However, when the fluid pressure supply falls and / or during pulling of the pipe out of the hole, there will then be a net upward force acting on the head seal 26, whereby the sleeve 16 will rise to the upper position shown in Figure 1, whereby the tail seal 29 uncovers access to the discharge port 28, whereby fluid in the fitting can be discharged readily via dump chamber 27 and discharge outlet ports 28.

As referred to earlier, floating piston 21 subdivides the annular chamber surrounding the sleeve into an upper chamber and a lower chamber, and with the lower chamber (20) communicating with the mud communication port 19. Below communication port 19 there is a seal ring 31, which defines a first chamber above it (20) which communicates with port 19, and a second chamber 32 below it (see Figure 2), and therefore seal ring 31 is exposed to a downward force derived from the annular fluid pressure transmitted via port 19 and chamber 20, but is also exposed to an upward force derived from chamber 32 and an internal balancing port 33 in the wall of the sleeve 16 which communicates with throughflow passage 17.The seal ring 31 therefore functions to hold or seal the pressure differential between the pump or drill string pressure (the pumped pressure in passage 17) and the annular pressure (in the annular space surrounding the drill string).

To summarise with regard to the operation of the first embodiment shown in Figures 1 and 2. when the pump flow rate and pressure increases, this pressure acts on the head seal 25 to compress the spring 26 and move the floating piston 21 downwardly. The sleeve 16 which is attached to the head seal 25 pushes through the seal ring 31 and also pushes a sealing sleeve portion 34 of tail seal 29 through the body to seal on sleeve seals 30. Internal balancing port 33 allows pressure to equalise between the seal ring 31 and the sealing sleeve portion 34.

This movement is achieved by having the pressure below head seal 25 (around compression spring 26 in annular chamber 18) effectively at "annular pressure" which will be lower than the pressure acting on the top of the head seal 25 which is exposed to pump pressure or drill string pressure. The annular pressure also acts on the floating piston 21. The underside of seal ring 31 is exposed to pump pressure (via port 33) and the top of seal ring 31 is exposed to the lower annular pressure derived from communication port 19 and chamber 20. The seal ring 31 is therefore designed to hold or seal the pressure differential between the pump or drill string pressure and the "annular pressure".

Mud communication port 19 is always exposed to annular pressure. shown schematically by reference 35 in Figure 1.

and allows the head seal 25, sleeve 16, floating piston 21 and sealing sleeve 34 to move until the sealing sleeve 34 seals on the sleeve seals 30 in the main body. When the pump pressure decreases, and the pressure equalises between the inside of the pipe and the annulus, the spring 26 returns the head seal 25 and sleeve 16 assembly to the upper "valve open" position shown in Figure 1. The sealing sleeve 34 moves away from the sealing sleeve seals 30, and this allows the mud or drilling fluid to drain out the flow ports 28.

The construction illustrated in Figures 1 and 2 can be changed to incorporate check valves (equivalent to check valves 23 and 24) and appropriate seals in an upper retainer ring 35. This will allow the pre-set closing pressure to be set higher than the spring force. This is another way of controlling the closing of the flow ports 28.

With check valves, the oil must be metered from oil chamber 18 through downward check valve 24. The check valves can be pre-set to determine activation pressure. For the tool to deactivate. oil must flow from oil chamber 22 through upward check valves 23 and into oil chamber 18. This allows the check valve to control the activation and deactivation pressures.

Figures 1 and 2 illustrate a first embodiment of tubular fitting for use in a drill string, which operates as a "dump valve" which can be opened and closed in response to variation in the supply pressure to the fitting. A modified embodiment is shown in Figures 3 and 4, in which floating piston 21, oil chamber 22 and upper retainer ring 35 are omitted. However, parts corresponding with those already described are given the same reference numerals, and will not be described in detail again.

In this modified embodiment, designated generally by reference 10a, drilling fluid or "mud" from the hole or annulus can pressurise annular chamber 18 via mud communication port 19. However, in this modified embodiment, the sealing ring 31 can be used to support the compression spring 26, as well as to seal the differential pressure which arises between pump pressure and annular pressure. Apart from these modifications. the embodiment 10a functions in generally similar manner to the first embodiment.

However, while the embodiments of Figures 1 and 2, and 3 and 4, can function as a "dump valve" pipe fitting in a drill string. in a further aspect of the invention they can be modified to function as a locking mechanism to lock a tool in position. Possible modification is shown in a further embodiment of the invention illustrated in Figure 5. For convenience only, this modified structure is derived from the embodiment of Figures 3 and 4, i.e. it lacks the floating piston 21, oil chamber 22, upper retaining ring 35 and check valves 23 and 24.

Accordingly. the "dump sub" embodiments of Figures 1 and 2, and 3 and 4, can be modified to function as a locking mechanism to lock or unlock a tool under differential fluid pressure action. In Figure 5, a locking mechanism is provided which is formed by a locking sleeve 40 and locking fingers 41.

In the "dump sub" arrangement, sealing sleeve 34 covers the sealing sleeve seals 30 when activated, or when there is pressure in the drill string. but when pressure equalises the compression spring 26 pushes the sealing sleeve 34 off the sleeve seals 30. In the locking mechanism design variant, upward and downward movement of the sleeve 16 activates or deactivates the locking sleeve 40 and locking fingers 41.

When the tool is activated, the locking sleeve 40 locks the fingers 41 in position. When the tool is deactivated, the locking sleeve 40 is pushed back off the fingers. allowing them to move freely.

The locking mechanism variant is a useful alternative inventive concept. Thus, there are conventional arrangements in which tools which must be locked in position for certain reasons have locking mechanisms which work under direct action of flow of the fluids. The looking mechanism according to the invention, as shown by the example of Figure 5, does not activate itself by means of flow as such, but is activated using the pressure differential between the drill string and the surrounding hole or annulus. When drilling occurs, there is higher pressure in the drill string than in the hole or annulus, and this pressure differential causes the tool to activate. However, when the pressure in the drill string is reduced and equalises with the pressure in the hole or annulus, the tool deactivates.

Claims (10)

1. A tubular fitting for use in a drill string to be positioned above a working or drilling tool coupled with the drill string, said fitting comprising: a cylindrical housing having an inlet at its upper end for admitting drilling fluid or "mud", and an outlet at its lower end for discharging the drilling fluid; a sleeve mounted for axial slidable movement within the housing between upper and lower positions, and defining a through-flow passage communicating with said inlet and with said outlet; an annular chamber defined between the inner wall of the housing and the outer wall of the sleeve; inlet means in the wall of the housing for communicating the usual annular pressure surrounding the drill string in service with said annular chamber;; a head seal provided at the upper end of the sleeve and arranged to have its upper face exposed to the pressure prevailing at the inlet in order to exert a downward force on the sleeve, and its lower face exposed to the pressure prevailing in said annular chamber to exert an upward force on the sleeve; biasing means for applying an additional upward force to the head seal; a dump chamber at the lower end of the housing; a discharge outlet in the wall of the housing near the lower end thereof and communicable with said dump chamber; and, a tail seal provided at the lower end of the sleeve and movable upwardly and downwardly with the sleeve depending upon the direction of the net force acting upon the head seal, said tail seal closing access to said discharge outlet when the sleeve is in the lower position whereby fluid supplied to the inlet can pass straight through the fitting, and said tail seal allowing access to the discharge outlet when the sleeve is in the upper position whereby fluid in the fitting can be discharged via the dump chamber and the discharge outlet.

2. A tubular fitting according to Claim 1, in which the biasing means takes the form of a compression spring housed within the annular chamber, and acting directly on the underside of the head seal.

3. A tubular fitting according to Claim 1 or 2, in which an annular floating piston is slidable within the annular chamber which it subdivides into an upper chamber and a lower chamber, and with the lower chamber communicating with said inlet means which admits annular pressure to the fittings.

4. A tubular fitting according to any one of Claims 1 to 3, in which an internal balancing or transfer port is provided in the wall of the sleeve close to the tail seal.

5. A tubular fitting according to Claim 4, in which a seal ring surrounds the sleeve and is located by the housing at a position above said port and below the inlet means so that a chamber defined below the seal can received pumped fluid pressure from the sleeve to exert an upward force on the seal, in opposition to a downward force exerted on the seal ring by a second chamber above the seal ring which communicates with the inlet means.

6. A tubular fitting according to any one of Claims 1 to 5 and installed in a drill string to be positioned above a working or drilling tool coupled with the drill string.

7. A tubular fitting according to Claim 6, in which the tubular fitting is modified so as to function as a fluid pressure operated locking mechanism for a tool in the drill string.

8. A tubular fitting according to Claim 7, in which the discharge outlet is omitted, and a locking sleeve is coupled with the lower end of the sleeve of the fitting, referred to hereinafter as the main sleeve, and is movable up and down with the main sleeve as a consequence of variation in the differential pressure action on the head seal.

9. A tubular fitting according to Claim 8, in which locking fingers are coupled with the locking sleeve and arranged so that when the tool is activated the locking fingers are locked in position, but when the tool is deactivated, the locking sleeve is pushed back off the fingers allowing them to move freely, thereby unlocking the mechanism.

10. A tubular fitting according to Claim 1 and substantially as hereinbefore described with reference to, and as shown in the accompanying drawings.