The invention relates to top drive apparatus for drilling a borehole, for example a well such as an oil or gas well. In particular, the invention relates to top drive apparatus to permit entry of a wireline into the borehole while facilitating sealing of the borehole at the point of entry of the wireline.

Conventional systems and apparatus for permitting entry of a wireline into a borehole utilise a special section of drill pipe interconnected between the conventional drill pipe. This special section includes means to permit the borehole to be sealed around the wireline, which extends within the drill pipe, during wireline operations.

Such systems generally use a hydraulic pack-off system in which a grease is injected into the special section of tube and fills the annulus between the wireline and the inside of the tube section, to seal the borehole.

However, it is generally necessary to rotate the drill pipe and with conventional systems this is not possible

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while injecting fluid, such as grease, into the special tube section.

In accordance with the present invention, apparatus for permitting entry of a wireline into a borehole comprises a main housing having a through bore, through which the wireline extends in use, and coupling means on the housing to permit fluid to be fed from an external fluid source into the body of the housing, the coupling means comprising rotational coupling means to permit the fluid to be fed into the body of the housing during rotation of the housing relative to the external fluid source.

Preferably, the coupling means also includes a continuous channel disposed around the outside surface of the housing which is coupled to the external fluid source and which communicates with a fluid port extending into the body of the housing.

Typically, the rotational coupling means is adjacent the continuous channel and a fluid port in the rotational coupling couples the external fluid source to the continuous channel.

Preferably, the rotational coupling means comprises a bearing means to facilitate rotation of the housing relative to the external fluid source and typically, the fluid port in the rotational coupling means is substantially stationary relative to the external fluid source during rotation of the housing.

Preferably, more than one coupling means is provided on the housing and in one example, three coupling means are provided and may be axially spaced from each other

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on the housing.

However, in a second example five coupling means are provided and preferably, the rotational coupling means comprises a rotary hub on which the five coupling means are mounted.

Preferably, at least one of the coupling means is used to inject fluid into the body of the housing to seal the annulus of the through bore in which the wireline is located, in order to seal the borehole. The other coupling means, if present, may be used to direct fluid to other fluid operated devices in the housing, such as a tool catcher, a pack-off device or a fluid return line.

Two examples of top drive apparatus in accordance with the invention will now be described with reference to the accompanying drawings, in which:-

Fig. 1 shows a cross-sectional view of a first example of apparatus for permitting entry of a wireline into a borehole; Fig. 2 is a cross-sectional view of a tool catcher for use in the apparatus of Fig. 1 ; Fig. 3 is a cross-sectional view through a mechanical hydraulic piston type pack-off for use in the apparatus of Fig. 1; Fig. 4 shows a partial cross-sectional view through a second example of apparatus for permitting entry of a wireline into a borehole; Fig. 5 is an enlarged view of the lower section of Fig. 4; Fig. 6 is an enlarged view of the upper section of Fig. 4; and

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Fig. 7 is a cross-sectional view through the line AA of Fig. 5.

Fig. 1 shows a first example of apparatus 55 for permitting entry of a wireline 90 (see Fig. 3) into a bore hole. The apparatus has a main housing 10 having male 4 1/2 IF thread connector 11 at its lower end and a female 4 1/2 IF thread connector 12 at its upper end and a bore 13 extends through the housing 10. Adjacent the female connector 12, a stuffing box or pack-off assembly 2 is located, in the bore 13.

A packoff, sometimes referred to as a stuffing box, line wiper, oil saver, etc. seals the entry point of the wireline (or cable) 90 into a pressurised riser, minimising or eliminating' fluid and gas losses. Although packoffs differ slightly in design, their use and operating characteristics are quite similar. The packoff is indicated by reference numeral 2 in Fig. 1 and is shown in more detail in Fig. 3.

Packoffs also prevent the exposure of personnel on location to harmful chemicals and/or gases that are present in the well, minimise or prevent pollution of the well site and atmosphere and reduce the risk of fire on location. Obviously, the packoff is an extremely important piece of equipment and must be kept in good working condition at all times.

Although some packoffs have more internal parts than others, the basic packoff consists of a housing or body 91, a packing element or line rubber 92, and a device for compressing the packing element. The inside diameter of the body is of sufficient size to allow the passage of the logging cable 90 and cable head. Some

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have diameters large enough to pass large logging tools and large diameter perforating guns.

The packing element (line rubber) 92 is either slit down one side or cut in halves lengthwise to allow quick replacement. The packing element which seals around the cable is housed inside the packoff body 91 so that outward expansion or elongation of the element is very limited. To compress the element, directional force is applied to it from above, below, or around the outside. The packing element 92 is a high wear item and must be replaced often. On certain jobs it may be necessary to replace the element after each run. Packing element 92 wear is a function of cable size, surface condition, lubrication, the force required to maintain seal, footage arid gland design. Some devices wear the rubbers evenly throughout and can tolerate much wear while others wear out at the upper end and must be replaced often.

Packing element 92 is compressed to the desired gland tightness remotely by means of a hydraulic hand pump and hose. This allows the operator to control the pack-off from a distance, which is very important where toxic gases are present. Below the packoff assembly 2, a flow tube assembly 3 is located. The flow tube assembly 3 is located within a grease seal control head 20.

The grease seal control head provides a leak free entry for conductor wirelines into high pressure oil or gas wells without undue hazard and with protection of the environment. There is negligible wear on the components and low drag on the cable.

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As injected grease can seal over irregular forms such as stranded cable, even large diameter conductor wireline can be sealed against gases over lengthy operations. Generally, however, jobs under pressure are done with monocables since pressures of 5,000 and 10,000 psi or even greater are experienced. The pressure acting on the cross-sectional area of the cable, is much less for a monocable than for a heptacable (5000 psi well pressure exerts an upward force of 860 lbs on a 15/32 cable but only 190 lbs on a 7/32 monocable) .

Flowtubes are tubes some 14 inches long which have an inside diameter only slightly larger than the cable (of the order of .004" larger). Two to five or more of these tubes are used. Grease is pumped in between the tube and the cable. The flowtubes are able to seal against well pressure because of the resistance to flow of a viscous fluid passing through a restriction. Since the laws of fluid mechanics governing the behaviour of greases are outside the scope of this description, it will suffice to say that grease in the tube is able to withstand a pressure gradient P/L which is in excess of that which can be developed by the well fluids assuming the difference between the cable OD and the tube ID is small.

The space between the cable and flowtubes must be small. The difference between the outside diameter of the cable and the inside diameter of the tube may vary from approximately 0.004" to 0.01". As the tube gets worn during continued use, the grease consumption increases. However, if the tube becomes too worn a seal can no longer be maintained because the pressure gradient the grease is able to withstand will be

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smaller than that imposed by the well fluids. Hence it is important to match flowtube and cable size, taking into account the amount of wear of both tube and cable.

The grease must be viscous. Well fluids can pass through the flowtube due to their low viscosity. The grease is only effective if it has a high viscosity. Fluids in the well, such as distillate or diesel can reduce the viscosity of the injected grease.

Grease must be injected at a higher pressure than well pressure. Grease is injected through a check valve at the lower port of the grease head. Excess grease is drained from the top port though the drain hose (flowline) and out the flowline valve into a container that is open to atmosphere.

Immediately adjacent and below the flow tubes 3 , a ball check valve assembly 4 is provided and below this a tool catcher assembly 5. The ball check valve assembly 4 and tool catcher assembly 5 may be incorporated into a combination tool 51, as shown in Fig. 2.

Fig. 2 shows a combination tool in which a hydraulic inlet 50 is coupled directly to the combination tool 51 which incorporates a head catcher and ball check valve in one housing. The ball check valve requires a fluid pressure to force the ball up into its seat.

The head catcher is a hydraulically operated tool with a moving piston. The tool is always in the CATCH position unless pressure is applied to force the piston upwards into the RELEASE position.

- CATCHING

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With no pressure applied to the hydraulic piston, the piston spring forces the piston down. When the piston is at the bottom of its travel the collet is collapsed - the collet is segmented and held together by the garter spring. When the fishing neck contacts with the collet it pulls the collet up and compresses the collet spring. At the same time as pulling upwards it is also trying to push outwards to open the collet. After sufficient travel the collet will have opened sufficiently to allow the fishing neck to pass. The fishing neck will stop at the tool stop and the collet spring will expand and force the segmented collet to close around the fishing neck. The segmented collet is wedged closed by the bevelled shoulder on the lower body and the downwards acting force of the collet spring. The wireline tool is now safely caught and will not go downhole until released. Slack can be now put in the wireline as tension is not required to keep the wireline tool caught.

- RELEASING

To release tools from the head catcher hydraulic fluid is pumped via the hydraulic coupling to the lower side of the piston. This will force the piston upwards. Before releasing all slack must be taken out of the wireline to ensure the wireline tools do not fall suddenly and jar the weak point.

As the piston moves upwards the collet assembly is lifted and the collet spring compressed. The collet segments are forced open by the bottom edge of the tool stop as it comes in contact with the inside bevelled shoulder of the collet. The fishing neck is now released and the wireline tools can be lowered in the

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well.

It is good operating practise to keep the head catcher in the CATCH position at all times when in the hole.

- BALL CHECK VALVE

The ball check valve only comes of use when, for some reason, the wireline has been pulled out of the grease head and there is pressure in the well. It will thus prevent a blow-out through the flow tubes.

The principle of operation in this assembly relies on fluid in the annulus around the ball seat to force the ball upwards and into the seat. The is achieved by maintaining a small clearance around the ball making it pressure sensitive. Injected grease aids in reducing the differential pressure required across the ball.

Tests have shown that with water in the well the ball check valve will seal at pressures as low as 15 psi. With air this sealing pressure is increased to 125 psi but is improved when grease is packed into the ball cavity. The test with air and a greased ball cavity produced a sealing pressure of 10 psi.

Fluid ports 40, 41, 42 (Fig. 1) extend through the body of the housing 10 to permit fluid to be injected into the packoff assembly 2, flow tube assembly 3 and the tool catcher assembly 5, respectively. Located adjacent each of the fluid ports 40, 41, 42 and mounted externally on the housing 10 is a bearing assembly 1.

Each bearing assembly 1 has a fluid port 6 thereon which permits a fluid conduit to be coupled to the

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bearing assembly 1. The bearing assemblies 1 are rotationally mounted on the housing 10 so that when the housing 10, which forms part of the drill string is rotated, the fluid ports 6 remain stationary.

A circumferential channel is formed between each bearing assembly 1 and the surface of the housing 10 so that the parts 6 and 40, 41, 42 remain in fluid communication with each other via the channel, irrespective of the orientation of the housing 10 relative to the fluid ports 6.

Hence, fluid may be injected into the ports 40, 41, 42 during rotation of the housing 10.

Figs. 4 to 6 show a second example of apparatus 60 for permitting entry of a wireline into a borehole. The apparatus 60 is similar to the apparatus 55 shown in Fig. 1. However, the apparatus 60 has five fluid ports 61, 62, 63, 64, 65, each of the fluid ports 61-65 being located on a respective hub unit 66, 67, 68, 69, 70 which together form a five port rotary hub 71 which is mounted by thrust washers 84, 85 on body section 83 of the apparatus 60. The hub 71 is secured on the body section 83 by a lock nut 86 at its upper end and a flange 87 formed on the body section 83 at its lower end. Fig. 7 is a cross-sectional view on the line A-A in Fig. 5 and shows that each of the ports 61-65 are spaced from each other around the circumference of the rotary hub 71. Each fluid port 61-65 is in fluid communication with a respective fluid bore 72, 73, 74, 75, 76. Each fluid bore 72, 73, 74, 76 extends through the rotary hub 71 in a direction parallel to the longitudinal axis of the apparatus 60. Fluid bore 75 extends in a radial direction from fluid port 64

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through body section 83 into the central bore 13. The fluid bore 72 is coupled to a conduit (not shown) which conveys fluid from the fluid port 61 to a cable wiper inlet 77. Fluid bore 74 is coupled to a conduit (not shown) which conveys fluid from the fluid port 63 to a hydraulic pack-off inlet 78 for pack-off 2. Fluid bore 73 is coupled to conduit 79 which conveys grease from the wiper unit via outlet 81, and from the flow tubes assembly 3 to fluid port 62 which returns the grease from the wiper and flow tube assembly 3 to a collecting tank. Fluid bore 75 is coupled into central bore 13 of the apparatus 60 to feed grease into the flow tube assembly 3. The grease then returns from the flow tube assembly via outlet 80 and conduit 79 to the wiper/grease return fluid port 62. Fluid bore 76 coveys fluid from fluid port 65 to tool catcher port 82 via conduit 83 to operate tool catcher 5.

Each of the hub units 66-70 are in the form of rings which are mounted on body section 83 of the tool 60 by means of thrust washers 84, 85 which permit rotational movement of the hub units 66-70 relative to the body section 83. The hub units 66-70 are mounted on the body section 83 by means of thrust washers 84, 85 such that each of the fluid ports 61-65 communicates with an annular channel formed between each hub unit 66-70 and body section 83 and each annular channel communicates with the respective fluid bore 72-76. Hence, fluid ports 61-65 are maintained in fluid communication with the respective fluid bores 72-76 irrespective of the angular orientation of the fluid ports 61-65 relative to the respective fluid bores 72-76. This has the result that the hub units 66-70 and fluid ports 61-65 therein can be maintained stationary during rotation of the body section 83 of the apparatus 60 and fluid may

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pass through the fluid ports 61-65 into or out of the tool 60 during rotation of the body section 83.

Modifications and improvements may be incorporated without departing from the scope of the invention.

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