GB2457317A

GB2457317A - A drill-string connector

Info

Publication number: GB2457317A
Application number: GB0805299A
Authority: GB
Inventors: George Swietlik; Burney J Laitolais Jr; Robert Large
Original assignee: Pilot Drilling Control Ltd
Current assignee: Pilot Drilling Control Ltd
Priority date: 2008-02-08
Filing date: 2008-03-20
Publication date: 2009-08-12
Also published as: ATE530730T1; WO2009098474A1; WO2009098473A3; EP2255059B1; EP2255059A1; GB0805299D0; CA2715073A1; WO2009098473A2; BRPI0905957A2; WO2009098478A2; WO2009098478A3; WO2009098482A1

Abstract

A connector 10 which provides a fluid tight connection between a fluid supply and a downhole tubular (4fig.1), e.g. a top drive and a drill string, the connector 10 comprising a body portion 15 and an extendable portion (piston rod) 20, the extendable portion having a seal 130 at or towards its free end which is adapted to sealingly engage the downhole tubular when the extendable portion is at least partially extended from the body portion, the extendable portion comprising a pressure face(piston) 50 exposed to a fluid in the body portion, so that the extendable portion extends by virtue of the fluid pressure of the fluid in the body portion 70 acting on the pressure face, the connector also comprising a first valve 140 provided on the pressure face of the extendable portion, the first valve being a one-way flow valve permitting flow from the downhole tubular in to the connector. The extendable portion may also comprise a filter 200.

Description

1 2457317 A drill-string connector This invention relates to a connector which establishes a fluid tight connection to a downhole tubular and may, for example, establish a fluid tight connection between a downhole tubular and a top-drive

Background

It is known in the oil and gas industry to use a top drive motor and a drill-string to drill wells. It is the top drive motor that provides the torque to rotate the drill-string, which in turn rotates the drill bit at the bottom of the well. The drill-string itself consists of a series of hollow pipes, typically 3Oft (9.14m) in length, and these are attached to each other via a threaded connection. The top drive is also attached to the drill-string via a threaded connection.

During the drilling process, drilling mud is pumped through the connection between the top drive and the drill-string This drilling mud travels through the drill-string and ensures sufficient lubrication, cooling and the removal of cuttings. It is often necessary to remove the drill-string from the well (to replace the drill bit for example) and under such circumstances drilling mud is pumped through the drill-string to displace and support the retreating drill-string and maintain hydraulic balance in the well bore. This ensures that a vacuum is not created and that the force required to remove the drill-string is minimised, allowing the removal to occur more quickly. In a conventional arrangement, the drilling mud is pumped through the same connection, between the top drive and drill-string, as used when drilling.

When removing a drill-string from a well (which in the industry is known as tripping-out), successive sections of the drill-string have to be disconnected from the remaining sections of the drill-string. Furthermore, the section being removed also has to be disconnected from the top drive. A new connection is then established between the top drive and the remaining sections of the drill-string However, making and breaking these threaded connections is very time consuming and slows down the process of removing a drill-string from a well. This has a serious impact on the productivity of the well.

Previous attempts have been made at speeding up the process of tripping-out.

GB2156402A discloses methods for controlling the rate of withdrawal and the drilling mud pressure to maximise the tripping-out speed However, the time taken to connect and disconnect each section of the drill-string to the top drive is not addressed Other attempts include removing several sections at a time, as discussed in GB2156402A.

However, this approach is limited by the height of the derrick holding the top drive.

GB2435059A discloses a device which comprises an extending piston-rod with a bung, which is selectively engaged with the top of the drill-string to provide a fluid tight seal between the drill-string and top drive. This arrangement obviates the need for threading and unthreading the drill-string to the top drive In other applications, it is often desirable to displace fluid from the Dorehole, prticuaiy when lowering the drill-string, for example, in deep water drilling applications In such deepwater applications the seabed accommodates equipment to support the construction of the well and the tubing used to line the well bore is hung and placed from this position. This is carried out by using a drill-string as a means of conveying and landing the tubing into position and as the drill-string is lowered, successive sections of drill-string have to be added It would therefore be desirable to use a device similar to that disclosed in GB2435059A to minimise the number of threaded connections required. However, as the bore of the drill-string is much smaller than the bore of the tubing, then fluid will be displaced and exit up through the drill-string. The device disclosed in GB2435059A is not suitable for such an application because it is not designed for fluid to flow up the drill-string, as there is a risk that the piston-rod would not stay in position. The present invention seeks to address these issues

Statements of Invention

According to a first aspect of the present invention, there is provided a connector which provides a fluid tight connection between a fluid supply and a downhole tubular, the connector comprising a body portion and an extendable portion, the extendable portion having a seal at or towards its free end which is adapted to sealingly engage the downhole tubular when the extendable portion is at least partially extended from the body portion, the extendable portion comprising a pressure face exposed to a fluid in the body portion, so that the extendable portion extends from the body portion by virtue of the fluid pressure of the fluid in the body portion acting on the pressure face, the connector also comprising a first valve provided on the pressure face of the extendable portion, the first valve being a one-way flow valve permitting flow from the downhole tubular in to the connector The extendable portion may comprise a filter.

According to a second aspect of the present invention, there is provided a connector which provides a fluid tight connection between a fluid supply and a downhole tubular, the connector comprising a body portion and an extendable portion, the extendable portion having a seal at or towards its free end which is adapted to sealingly engage the downhole tubular when the extendable portion is at least partially extended from the body portion, wherein the extendable portion comprises a filter.

The extendable portion may comprises a pressure face exposed to a fluid in the body portion, so that the extendable portion may extend from the body portion by virtue of the fluid pressure of the fluid in the body portion acting on the pressure face, the connector may also comprise a first valve provided on the pressure face of the extendable portion, the first valve may be a one-way flow valve permitting flow from the downhole tubular in to the connector.

The connector may also comprise a second valve, which may selectively permit flow from the connector to the downhole tubular. The second valve may be arranged such that it may be opened by the pressure of fluid from the fluid supply only when the seal is engaged in the downhole tubular The second valve may be provided in a parallel arrangement with the first valve between the downhole tubular and the fluid supply.

The extendable portion may extend when the pressure of the fluid in the body portion exceeds a threshold value. The seal between the connector and the downhole tubular may be provided by the location of a tapered bung in the open end of the downhole tubular.

The extendable portion may comprise a shaft and a cap, the shaft may be slidably mounted within the body portion and may extend through an end-cap in the body portion, and the cap may be provided on an end of the shaft within the body portion.

The connector may further comprise a piston and the piston may be slidably mounted on the shaft between the cap and the end-cap. The piston and cap may divide the body portion into first and second chambers, the first chamber may contain a first fluid and the second chamber may contain a second fluid.

The projected area of the cap exposed to the second chamber arid the projected area of the piston exposed to the second chamber may be selected so that the pressure force acting on the cap toward the first chamber may be greater than the pressure force acting on the piston when the extendable portion extends. The projected area of the cap exposed to the second chamber may be greater than the projected area of the piston exposed to the second chamber.

The shaft may be hollow and may provide a flow communication path between the second chamber and the downhole tubular. A hole forming part of the flow communication path may be provided in a side-wall of the shaft and the hole may be selectively covered by the piston, the hole and piston arrangement together forming the second valve.

In response to a pressure difference between the fluid in the first and second chambers and when the extendable portion may not be engaged with the downhole tubular, the piston and cap may move together, with the hole in the side-wall of the shaft covered by the piston. In response to a pressure difference between the fluid in the first and second chambers and when the extendable portion may be engaged with the downhole tubular, the piston may move independently of the cap, thereby enabling the hole in the side-wall of the shaft to be uncovered.

The first valve may be a one-way flapper valve provided on the cap. The first valve may be arranged so that the net pressure force acting on the extendable portion when the first valve is open may not be sufficient to move the extendable portion. Opening of first valve reduces the pressure loss between the downhole tubular and the fluid supply, thereby reducing the net pressure force acting on the extendable portion and preventing retraction of the extendable portion from the downhole tubular The first valve may open when there is a back-flow from the downhole tubular To receive back-flow, the supply of drilling fluid to the connector from the top-drive may be switched off and the air supply to the first chamber may also be switched off.

The filter may be provided in the shaft The bung may be detachable from the shaft.

The filter may comprise a flange which may be located between the detachable bung and the shaft such that the filter may also be detachable from the shaft.

The filter may be substantially tubular, with a closed end and an open end. The open end of the tubular filter may be closest to the downhole tubular and the closed end of the tubular may be furthest from the downhole tubular. The filter is self-cleaning due to its orientation. The filter may comprise a wire mesh. The filter may comprise a perforated tube.

According to a third aspect of the present invention, there is provided a connector which provides a fluid tight connection between a fluid supply and a downhole tubular, the connector comprising a body portion and an extendable portion, ihe extendabe portion having a seal at or towards its free end which is adapted to sealingly engage the downhole tubular when the extendable portion is at least partially extended from the body portion, the connector also comprising a first valve and a second valve, the first valve being arranged to open when the pressure of fluid from the fluid supply exceeds a threshold value, and wherein a second valve is provided in parallel arrangement with the first valve, the second valve being a one-way flow valve permitting flow from the downhole tubular to the connector.

The downhole tubular may be a drill-string or a casing section. The extendable portion may be a piston-rod. The body portion may be a cylinder.

The first chamber may contain air, which may be selectively compressed. The second chamber may contain drilling-fluid or drilling mud.

According to a fourth aspect of the present invention, there is provided a connector which provides a fluid tight connection between a fluid supply and a drill-string, the connector comprising: a piston-rod and a cylinder, the piston-rod having a seal at or towards its free end which is adapted to sealingly engage the drill-string when the piston-rod is at least partially extended from the cylinder; and a threaded portion provided on the cylinder, the threaded portion being adapted to engage with a threaded section in an open end of the drill-string; wherein the piston-rod extends through the threaded portion.

The seal between the connector and the drill-string may be provided by the location of a tapered bung in the open end of the drill-string The seal may be detachable from the piston-rod The seal may be interchangeable with one or more alternative seals. The connector may connect to the drill-string via the threaded portion engaging with a corresponding threaded section in the open end of the drill-string.

The seal may be provided on a shaft, the shaft being detachable from the piston-rod.

The shaft may be threadably engaged with the piston-rod. The shaft may be threadably engaged to the piston-rod with a stub-acme connection A connection between the piston-rod and shaft may act as a sacrificial connection such that if an impact load is applied to the shaft, the piston-rod and cylinder may be protected. The connection between the piston-rod and shaft may be box weak.

The piston-rod may be retractable within the threaded portion, so that when the seal is detached the piston-rod may not be exposed beyond the end of the threaded portion.

The piston-rod may fit inside the interior of the drill-string beyond the threaded section in the open end of the drifl-string. The piston-rod may be provided with a mechanical stop limiting the retraction of the piston-rod into the cylinder.

The piston-rod may provide a flow communication path between the fluid supply and the drill-string. The piston-rod may be hollow and the shaft may be hollow.

The threaded portion may be provided on a threaded member disposed about the piston-rod and the threaded member may be detachable from the cylinder. The threaded member may be threadably engaged with the cylinder. The threaded member may be interchangeable with one or more alternative threaded members.

The piston-rod may be provided with a keyway. The threaded member may be provided with a key and the key may interface with the keyway of the piston-rod so that rotation of the piston-rod may be prevented. The key and keyway may provide the mechanical stop limiting the retraction of the piston-rod.

The threaded member may be provided with a port and the port may act as a vent for fluid displaced in the cylinder by movement of the piston-rod.

The connector may be capable of transmitting torque from a top-drive to the drill-string via the threaded portion engaging with the threaded section of the drill-string. All threaded connections may be orientated in the same direction. The threaded portion may comprise a standard pin connection The threaded section in the open end of the drill-string may comprise a standard box connection

Brief Description of the Drawings

For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the following drawings, in which: Figure 1 is a schematic of the connector and shows the connector in position between the top drive and the drill-string; Figure 2 is a sectional side projection of the connector according to a first embodiment of the invention and shows the connector prior to engagement with the drill-string; Figure 3 is a sectional side projection of the connector according to a first embodiment of the invention and shows the connector when engaged with the drill-string; Figures 4a and 4b are more detailed sectional view of the connector according to a first embodiment of the invention and show the connector in position to transfer drilling mud to the drill-string with the first valve in a closed position (Figure 4a) and the connector receiving back-flow with the first valve in an open position (Figure 4b), and Figures 5a and 5b are more detailed sectional views of the connector according to a second embodiment of the invention and show the connector in a retracted position (Figure 5a) and a concealed position (Figure 5b).

Detailed Description of the Preferred Embodiment

With reference to Figure 1, a drill-string 4 is removed from, or lowered into, a well by using a top drive 2. The drilt-string 4 is connected to the top drive 2 in two ways.

Firstly, elevators 6 clamp around the drill-string 4, and these transmit the force required to raise (or lower) the drill-string 4. Secondly, the top-most section 3 of the drill-string 4 is provided with a female thread which engages a male threaded connector 5 on the top drive 2 to provide a connection to allow drilling mud to be pumped into the drill-string 4. Once a section of the drill-string 4 is removed from the well it must then be disconnected from the rest of the drill-string 4 and the top drive 2 before it can be taken away (or racked into the derrick (not shown)) The remaining sections of the drill-string 4 are held in place by conventional slips on a rotary table (not shown) In conventional arrangements, the join between the top drive 2 and the drill-string 4 is a threaded connection Making and breaking this connection is time consuming, particularly when removing, or installing, an entire drill-string 4.

Similarly, the top drive 2 can lower a drill-string 2 into a well bore and the reverse procedure is applied. The drill-string may be lowered into a well bore for further drilling or to lower casing sections into the well bore, for example in a deep-sea driiiing application. The present invention relates to these and other applications and specifically relates to an alternative means for establishing the connection between the top drive and the drill-string or any other downhole tubular.

With reference to Figure 2, a connector 10, according to a first embodiment of the invention, comprises a cylinder 15 and a piston-rod 20, the piston-rod 20 being slidably engaged in the cylinder 15 The piston-rod 20 further comprises a hollow tubular 30, on which is mounted a cap 40, the tubular 30 being slidably engaged in the cylinder 15 such that a first end of the tubular 30 protrudes outside the cylinder 15 and a second end is within the cylinder 15. The cap 40 is mounted on a second end of the tubular 30, whilst on a first end of the tubular 30 there is located a bung 60 with seals 130.

The bung 60 is preferably made from nylon and is shaped to fit into the top end of the drill-string 4, i.e the box section.

A tubular filter 200 is disposed between the first end of the tubular 30 and the bung 60.

The filter 200 is substantially cylindrical with a closed end and an open end between its side-walls. The open end of the filter 200 comprises an outer-flanged portion about its circumference, which abuts the first end of the tubular 30. The bung 60 threadably engages the first end of the tubular 30 and an abutment shoulder within the bung 60 abuts the flanged portion of the filter 200 so that the filter 200 is secured between the tubular 30 and bung 60. In this manner the bung 60 and filter 200 are readably disconnected from the tubular 30, thereby allowing the bung 60 and/or filter 200 to be replaced and/or cleaned.

The filter 200 is arranged with its open end facing the bung 60 and the closed end facing the cap 40, so that the filter 200 is primarily within the tubular 30. In other words, a flow from the drill-string 4 to the connector 10 flows firstly into the open end of the filter and then through the side-walls and closed end of the filter 200. The filter 200 is sized so that a sufficient gap is provided between the side-walls of the filter and the tubular 30, whilst maintaining a sufficient internal diameter of the filter. The dimensions of the filter 200 relative to the tubular 30 are selected so as to reduce the pressure drop across the filter. The filter 200 comprises a perforated pipe, with the closed end also being perforated. In alternative embodiments the filter may comprise a wire mesh or any other conventional filter arrangement.

The tubular 30, cylinder 15, bung 60 and cap 40 shown in Figure 2 are arranged such that their longitudinal axes are coincident At the end of the cylinder 15, beyond which the tubular 30 protrudes, there is mounted an end-cap 42. The end-cap 42 seals the inside of the cylinder 15 from the outside, whilst also allowing the tubular 30 to slide in or out of the cylinder 15. Seals, such as 0-ring seals 25 are used to seal between the end-cap 42 and tubular 30.

The connector 10 further comprises a piston 50. The piston 50 is slidably mounted on the tubular 30 inside the cylinder 15 and is free to move between the cap 40 and the end-cap 42. The whole assembly 20, 40, 50 and 60 is also able to slide in the cylinder 15. The inside of the cylinder 15 is divided by the piston 50 to form a first chamber 80 and a second chamber 70. The projected are of the piston 50 is less than the projected area of the cap 40 such that when the piston 50 abuts the cap 40, the pressure force from the fluid in the second chamber 70 acting on the cap 40 is greater than that acting on the piston 50.

The first and second chambers 80 and 70 preferably hold air and drilling mud respectively. The piston 50 is sealed against the tubular 30 and cylinder 15, for example by means of 0-ring seals 52 and 54, to ensure no flow communication between the two chambers 70 and 80. The first chamber 80 is in flow communication with an air supply via a port 100, which is capable of selectively pressurising the air in the first chamber 80. The second chamber 70 is provided with drilling mud from the top drive 2 via a socket 90, which is a conventional box-pin connection. The top drive 2 is connected to the connector 10 via the engagement of a cooperating threaded connection (not shown).

In the disposition of components shown in Figure 2, the piston 50 and cap 40 are touching, so that drilling mud cannot flow from the second chamber 70 to the drill-string 4. Figure 3 shows an alternative disposition of the cap 40 and piston 50. With the cap and piston 50 apart, holes 120 are exposed in the side of the cap 40. These holes provide a flow communication path between the second chamber 70 and the interior of the hollow tubular 30. Thus drilling mud can flow from the second chamber 70 to the drill-string 4, via the holes 120 in the cap 40 and the hollow tubular 30.

Figures 4a and 4b show further detail of the structure of the cap 40 and piston 50. In particular, the flow communication path between the second chamber 70 and Uie hollow tubular 30, via the holes 120, is further highlighted.

Also shown in figures 4a and 4b is a valve 140 located on the cap 40. The valve 140 is a one-way flapper valve, which pivots with respect to the cap 40 by virtue of a hinge. In an open position, the valve 140 provides a flow path from the hollow tubular 30 to the second chamber 70 and conversely when the valve is in a closed position this flow path is blocked. The valve is in a closed position when the pressure of the fluid in the second chamber 70 exceeds that in the hollow tubular 30 The valve 140 will open if the pressure in the hollow tubular 30 exceeds the pressure in the second chamber 70.

The valve 140 is plug shaped with tapered side-walls so that a pressure seal is formed between the valve 140 and cap 40 when the pressure in the second chamber 70 exceeds that in the hollow tubular 30. The valve 140 is also spring biased into a closed position.

With reference to Figure 5a, the bung 60, according to a second embodiment of the invention, further comprises a detachable shaft 105. The detachable shaft 105 is threadably attached to the tubular 30 and is selectively detachable from the tubular 30.

The seals 130 are provided around the outside of the detachable shaft 105. The detachable shaft 105 is hollow to allow the flow of drilling fluid from the top drive 2, through the tubular 30, and into the top of the drill-string 4 The detachable shaft 105 and attached seals 130 are interchangeable with alternative shaft and seal arrangements. This facilitates the repair and replacement of worn seals, or differently shaped bungs could be deployed for different drill-strings Furthermore, the connection between the tubular 30 and the detachable shaft 105 can be made deliberately weak, so that it acts as a sacrificial connection. If an impact load is applied to the bung 60 the connection will tend to fail, so that the piston-rod 20 and cylinder 15 are protected from damage. For example, the detachable shaft 105 may be provided with a female threaded socket, which engages with a corresponding male thread on the tubular 30, and the female threaded socket of the detachable shaft 105 may be deliberately weakened at its root so that it will fail before damage occurs to the tubular 30. As for the first embodiment, the filter 200 is located between an abutment shoulder in the female threaded socket of the detachable shaft 105 and the male thread on the tubular 30.

The second embodiment of the invention also comprises a inreaded rntriiber 110, which is also provided on the first end plug 42. The threaded member 110 is connected to the first end plug 42 by virtue of a threaded connection and the threaded member 110 is hollow to allow the tubular 30 to pass through it. The threaded member seals the inside of the cylinder 15 from the outside, whilst also allowing the tubular to slide in or out of the cylinder 15. In an alternative embodiment, the threaded member 110 and end-cap 42 are integral and comprise a single component.

The end of the detachable shaft 105, which attaches to the tubular 30, has the same or smaller external dimensions as the tubular 30. This ensures that the detachable shaft fits inside the threaded member 110. Furthermore, the detachable shaft 105 has a protrusion 106, which acts as a mechanical stop limiting the retraction of the piston-rod 20 into the cylinder 15. The protrusion 106 is shaped with spanner flats so that the detachable shaft 105 can be removed from the tubular 30.

With reference to Figure 5b, the tubular 30 further comprises an abutment shoulder 150, which is formed by a flat portion on the outer surface of the tubular 30 being adjacent to a cylindrical portion. The flat portion on the surface of the tubular 30 provides a keyway and the threaded member 110 is provided with a corresponding key 160. The key 160 interfaces with the keyway of the tubular 30 so that rotation of the tubular 30 is prevented, thereby facilitating removal of the detachable shaft 105.

Furthermore, the tubular 30 may be fully retractable within the threaded member 110 when the detachable shaft 105 is removed, such that the tubular 30 does not extend beyond the end of the threaded member 110. The key 160 and keyway also provide a mechanical stop limiting the retraction of the piston-rod 20 when the detachable shaft is removed The threaded member 110 is further provided with a threaded section 170. In one mode of operation the threaded section 170 is threadably connected to the open end of the drill-string 4 and the connector 10 is therefore capable of transmitting torque from the top-drive 2 to the drill-string 4. Accordingly, in order to transmit drive, the threaded connections between the top-drive 2, socket 90, threaded member 110 and drill-string 4 are orientated in the same direction.

The detachable shaft 105 and hence bung 60 are removed from the tubular 30 when the threaded member 110 is connected to the drill-string 4. The tubular 30 is sized so that it fits inside the interior of the drill-string beyond the threaded section in the open end of the drill-string Alternatively, the tubular 30 may also be retracted into the threaded member 110.

In an alternative embodiment, the detachable shaft 105 need not be removed from the tubular 30 when threading the threaded member 110 to the drill-string The connector may then connect to the drill-string by virtue of both the bung 60 and the threaded member 110. Such an alternative embodiment would allow rapid deployment of the threaded connection without having to remove the detachable shaft 105, thereby saving time and money. In order to enable the engagement of the threaded member with the drill-string 4 without removing the detachable shaft 105, the protrusion 106 may be smaller than that shown in figure 5a. For example, the protrusion may not extend radially outwardly beyond the radially outer surface of the bung 60 and/or threaded section 170.

The threaded member 110 is removable from the end cap 42 and as such is interchangeable with alternative threaded members. This facilitates repair of the threaded member 110 andlor enables differently shaped threaded members to be deployed to suit the particular drill-string 4 in use Other than the aspects described above, the second embodiment is substantially the same as the first embodiment.

Operation of the connector 10 according to the first and second embodiments will now be described. To extend the piston rod 30, so that the bung 60 and seal 130 engage the drill-string 4, the pressure of the drilling mud in the second chamber 70 of the connector is increased by allowing flow from the top drive 2. The air in the first chamber 80 is at a pressure sufficiently high to ensure that the piston 50 abuts the cap 40. As the pressure of the drilling mud increases, the force exerted by the drilling mud on the piston 50 and cap 40 exceeds the force exerted by the air in the first chamber on the piston 50 and the air outside the connector 10 acting on the piston-rod 20. The cap 40 is then forced toward the end-cap 42 and the piston-rod 20 extends As the projected area of the cap 40 is greater than the projected area of the piston 50 and the air pressure in the first chamber 80 is only exposed to the piston 50, the piston 50 remains abutted to the cap 40. Thus, whilst the piston-rod 20 is extending, the holes are not exposed and drilling mud cannot flow from the top drive 2 into the driii-string 4. Furthermore, as the pressure of the drilling mud in the second chamber 70 exceeds the pressure of the air within the hollow tubular 30, the valve 140 also remains closed.

Once the bung 60 and seals 130 are forced into the open threaded end of the drill-string 4, thereby forming a fluid tight seal between the piston-rod 20 and the open end of the drill string 4, the piston-rod 20, and hence cap 40, are no longer able to extend.

By contrast, as the piston 50 is free to move on the tubular 30, the piston 50 is forced further along by the pressure of the drilling mud in the second chamber 70 The holes are thus exposed and drilling mud is allowed to flow from the second chamber 70, through the piston-rod 20 and into the drill-string 4. With the holes 120 open, the connector 10 will ensure that the volume displaced by the removal of the drill-string 4 from the well is replaced by drilling mud. The pressure of the air in the first chamber 80 can then be released until retraction of the piston-rod 20 is required.

If the piston-rod 20 extends fully without engaging a drill-string 4, the piston 50 will be prevented from lowering further by the end-cap 42. The holes 120 will therefore be unable to open and this ensures that no drilling mud is spilt if the piston-rod 20 does not engage a drill-string 4.

Alternatively, if the drill-string 4 is to be lowered into the well, then the drill-string 4 will displace fluid within the well and result in a back-flow into the connector 10 and top drive 2. Under such circumstances, or if there is back-flow for any other reason, the valve 140 will open, because the pressure of the fluid in the hollow tubular 30 is greater than the pressure of the drilling fluid in the second chamber 70. Furthermore, as the pressure of the air in the first chamber 80 is reduced, the piston 50 will be in its open position with flow through the holes 120 being permitted.

With the valve 140 open, the pressure drop across the piston-rod 20 will be negligible and the piston-rod 20 will remain engaged with the drill-string 4. Without the valve 140, there would be a significant pressure drop across the holes 120 and there would be a resulting tendency for the piston-rod 20 to withdraw from the drill-string 4. The valve 140 therefore allows the connector 10 to be used in both lowering and removal modes of operation.

Finally, when it is desired to retract the piston-rod 20 from the drill-string 4, the pressure of the air in the first chamber 80 is increased. The top-drive's drilling mud pumps will also be stopped to reduce the pressure of the drilling mud in the second chamber 70. The force exerted on the piston 50 by the drilling mud is then less than the force exerted on the piston 50 by the air, the piston 50 is biased towards the cap 40 and socket 90. The piston 50 forces the retraction of the piston-rod 20 into the cylinder 15. The piston 50 also abuts the cap 40, thereby closing the holes 120 and ensuring no drilling mud flows out of the connector 10. Furthermore, the movement of the cap will cause the valve 140 to close and the resulting increase in pressure in the second chamber 70 will ensure that the valve 140 is sealed and that no drilling mud leaks from the retracting piston-rod 20. When the piston-rod 20 is retracted, the bung and the seals 130 are disengaged from the drill-string 4 and the top most section of the drill-string 4 can be removed During back-flow, when drilling fluid flows from the drill-string 4 to the top drive 2, the filter 200 filters out any debris and particulate matter and thereby protects the connector, in particular the valving arrangements The orientation of the filter 200 encourages any debris to collect at the closed end of the filter, i.e. the top-most end.

Thus, when the flow is reversed such that drilling fluid flows from the top drive 2 to the drill-string 4, the debris that has collected at the closed end of the filter is flushed back into the well-bore. The filter 200 is therefore self-cleaning due to its orientation. By contrast, if the lilter 200 were orientated with the closed end facing the drill-string 4, debris would collect about the flange of the filter during back-flow. Reversal of the flow (i e. toward the drill-string 4) would then not be as effective at removing the debris from around the flange There would then be an accumulation of debris and a resulting increase in the pressure loss across the filter.

As described above, the connector 10 replaces the traditional threaded connection between a top drive 2 and drill-string 4 during the removal or lowering of a drill-string 4 from or into a well. With this connector, the connection between the top drive 2 and drill-string 4 can therefore be established in a much shorter time and great savings can be achieved