BACKGROUND TO THE INVENTION

The present invention relates to a penetrator comprising an electrical conductor for making an electrical connection across a barrier in an oil or gas well. In certain examples, the electrical conductor allows the connection of power and/or signal cables across the barrier. The penetrator of the invention is optionally useful for penetrating and forming a connection across wellhead barriers, but can also be useful for other barriers in the well, for example packers etc.

Electrical penetrators are specialised couplings which allow the connection of electrical cables across barriers of an oil or gas well, for example at the wellhead, or across a packer. SUMMARY OF THE INVENTION

According to the present invention there is provided a penetrator for use in penetrating a barrier in an oil or gas well, the penetrator comprising an electrical conductor for extending across the barrier, the conductor having an axis, a sleeve having an axial bore capable of receiving the conductor within the bore of the sleeve, the sleeve surrounding at least a portion of the axial length of the conductor, at least one tapered device disposed between the sleeve and the conductor, and a driver device adapted to compress the tapered device.

The invention also provides a method of making a connection across a barrier in an oil or gas well, the method comprising connecting an electrical conductor across the barrier, receiving at least a portion of the conductor within a bore of a sleeve, providing at least one tapered device between the sleeve and the conductor, and compressing the tapered device. The tapered device optionally comprises a sealing device, and is optionally compressed between the sleeve and the conductor, optionally against the sleeve. The penetrator optionally has at least one electrical connector to connect the conductor with a conduit (a power or signal cable etc.) on one side of the barrier with a conduit on the other side of the barrier. Optionally the penetrator has one electrical connector on each axially spaced end of the conductor, allowing connection of the conductor at each end to a conduit on either side of the barrier. The connector(s) on the conductor can optionally comprise sockets or plugs etc. Optionally more than one conductor is provided, each conductor having a connector at each end. The barrier is optionally a wellhead, and the penetrator is optionally a wellhead penetrator, but in certain examples, the barrier can be a packer e.g. below a wellhead in an oil or gas well.

Optionally, the compression of the tapered device between the sleeve and the conductor seals the bore of the sleeve.

Optionally, the sleeve insulates the conductor and resists passage of electricity.

Optionally the outer surface of the sleeve is ribbed. Optionally the ribs can comprise annular ribs, which optionally extend in a parallel array. Optionally the ribs can be mutually parallel. Optionally the ribs can be spaced apart on the axis of the sleeve, optionally at regular intervals. Optionally the ribs can extend radially from the outer surface of the sleeve. Optionally the radial extension of each rib is generally consistent with other ribs extending from the outer surface of the sleeve. Optionally the ribs are arranged in groups that may be spaced axially apart along the outer surface of the sleeve. For example, a group of ribs may be arranged at or near opposite ends of the sleeve, optionally at locations between the ends of the sleeve and a shoulder on the sleeve. Optionally each rib is spaced from at least one adjacent rib within each group.

Optionally one of the sleeve and the tapered device can comprise a hard material such as a ceramic. Optionally the other of the sleeve and the tapered device can comprise a more malleable material than the hard material, such as a metal, adapted to deform, optionally permanently in response to the compression applied by the driver device. Some examples of the tapered device can be formed from steel such as stainless steel. One example has an Inconel tapered device. One example has a copper/nickel alloy tapered device. Optionally the sleeve comprises a ceramic material. Optionally the sleeve can be moulded or cast. Optionally the sleeve can be sintered. The ceramic materials used are optionally in the Zirconia, Alumina and Silicon Nitride families. In one example, the ceramic material comprises Magnesia partially-stabilized zirconia or Mg-PSZ and in another the ceramic material can comprise Zirconia 3Y-TZP. Optionally the sleeve can have a coating (e.g. a conformal coating) or can be potted with a plastics or resin material such as epoxy to reduce or prevent fluid penetration into the sleeve, particularly to reduce the ingress of wellbore fluids from the lower end of the sleeve that is optionally exposed to wellbore pressure.

An electrical insulator can be disposed between the conductor and the sleeve. The electrical insulator can comprise a thin film layer or tape of plastics material such as PTFE or polyimide. The electrical insulator can optionally comprise a tape held in place on the surface of the conductor optionally with a high strength and high temperature adhesive. The electrical insulator layer can optionally sheath at least a portion of the conductor from the sleeve. The sleeve can optionally be disposed over the sheath of insulation.

Optionally the driver device comprises a tensioning device adapted to apply tension to the conductor, and to compress the tapered device between the sleeve and the conductor.

Optionally the driver device can comprise a thread or similar formation, and may interact with the conductor by means of cooperating screw threads or the like on the driver device and on the conductor. Optionally, the driver device can have a threaded socket with internal threads, and an externally threaded portion of the conductor can be received within the threaded socket. However, in other examples of the invention, the tensioning device can have an externally threaded portion, and the conductor can optionally have a socket that receives the same.

Optionally, the mating parts of the driver device and the conductor can be coated with a material having a low electrical resistance, optionally an inert conductive material, and optionally a metal. One optional material for coating the mating parts of the driver device and the conductor comprises silver or a silver alloy, or gold or gold alloy. Optionally the mating parts of the driver device and the conductor are threaded.

Optionally, the driver device can directly engage the sleeve, but in some examples, the driver device can be spaced from the sleeve, and can transfer force indirectly through a spacer or the like. Optionally, the tapered device can be at least partially annular, and optionally surround at least a part of the conductor. Optionally, the tapered device can comprise a ring. Optionally, the taper on the tapered device is formed by changing (e.g. decreasing) the radial depth of the tapered device in an axial direction.

Optionally, the tapered device can have more than one tapered end, for example two tapered ends. Optionally, the taper on each end face can be mismatched with the engaging faces on the tensioning device and/or the sleeve. Optionally, more than one tapered device can be provided, for example one tapered device can be provided at each end of the sleeve; for example, one of the tapered devices may be compressed between the sleeve and the conductor at one end of the sleeve, and the other tapered device may be compressed between the sleeve and the driver device at the other end of the sleeve. The tapered devices (where more than one is provided) may be the same or different, but optionally will have mismatching tapered faces for engagement with tapered faces on at least the sleeve, and optionally also the conductor and the driver device.

Optionally the conductor has a shoulder extending radially with respect to the axis of the conductor, optionally on the outer surface of the conductor and optionally extending radially away from the axis. Optionally the tapered device is compressed between the shoulder on the conductor and a shoulder on the sleeve. Optionally, the shoulder on the sleeve is provided at or by an end of the sleeve. Optionally, the shoulders on the conductor and the sleeve engage on faces which are at least partially tapered or chamfered. Optionally the taper on the engaging faces of the conductor and/or of the sleeve are mismatched with the taper on the faces of the tapered device. In other words, the angle of the engaging face of the tapered device can be slightly different from the angle of the engaging face on the shoulder which is engaged by the tapered engaging face of the tapered device. The mismatch between the engaging face of the tapered device and that of the shoulder of the conductor and/or the sleeve can be less than 5°, for example 1° or 2°. The mismatch between the tapered engaging faces can focus the force compressing the tapered device between the conductor and the sleeve on a relatively small surface area of the tapered device, which optionally forms a tight seal against the shoulder. Optionally one of the tapered device and the shoulder can deform (optionally permanently) as a result of the compression force exerted by the driver device.

In certain examples of the invention, the tapered face of the tapered device can be linear, but in other examples, the angle of the tapered face on the tapered device can vary between the axially spaced ends of the tapered face. For example, in certain examples, the angle of the tapered face on the tapered device can vary at a constant rate, or at a logarithmic rate with respect to the axial spacing along the tapered face. Accordingly, the tapered angle on the end of the tapered face adjacent to one end of the tapered face can approach the axis, and at the other end, can approach 0° with respect to the axis.

The tapered faces (on any of the components) can be tapered at constant angles, or can taper at varying angles, for example, one of the tapered surfaces (e.g. on the tapered device such as a seal ring) can have a tapered surface set at a constant angle, and the other tapered surface, for example on the end of the sleeve, can be arcuate, with a varying taper, or vice versa. Optionally one of the tapered surfaces engaging with the tapered device can be arcuate and one can be straight. Optionally the arcuate tapered surface can be formed on the sleeve, and the straight surface can be formed on the component on the other side of the tapered device, e.g. the driver device. Optionally the tapered surface of the tapered device on the side of the driver device can have the same taper angle as the component that engages it, optionally the driver device, or a spacer between the driver device and the tapered device. Thus, the mismatched taper angles are optionally provided on only one side of the tapered device.

Optionally, the tapered device can be formed from and/or coated with a material that is softer than the material of the sleeve. Optionally, the tapered device (or at least a surface, for example a coating of the tapered device) preferentially deforms (optionally permanently) against the sleeve when compressed by the driver device. Optionally, the tapered device is formed from a relatively hard material, optionally from a metal, and is optionally coated on at least its tapered surface with a relatively soft material. Optionally the tapered device deforms permanently when

compressed by the driver device. Optionally, at least one tapered device has an annular collar resisting radial deformation of the tapered device during

compression by the driver device. Optionally the annular collar is disposed radially outside the tapered device.

Optionally the sleeve and the conductor are received within a bore passing through the barrier, and are optionally sealed therein using mismatched tapers, optionally using tapered devices such as tapered rings. Optionally, the bore passing through the barrier has an engaging face, which compresses a seal ring having a tapered face between the engaging face of the bore and a shoulder extending radially from the sleeve, optionally from the outer surface of the sleeve. Optionally the seal ring seals on a radius.

Optionally, the bore which receives the sleeve can be formed in a penetrator body, and the penetrator body can optionally be sealed within the barrier using at least one compressed tapered device, optionally with mismatched tapered faces.

Optionally the body can be sealed in a penetrator housing in the same way. Optionally the tapered device can be sealed in a pocket. The angle between the sides of the pocket may be different from the angle between the faces of the tapered device received within the pocket.

Optionally at least one of the mismatched tapered faces is provided on a wedge shaped device, optionally the tapered device which is received within a pocket. Optionally the tapered device has an apex. Optionally the pocket has an apex, which optionally receives the apex of the tapered device. Optionally the apex of the wedge shaped device is deformed as the tapered device is compressed. Optionally the angle between the faces on either side of the apex of the wedge shaped device is different from the angle between the faces on either side of the apex of the pocket. Accordingly, the mismatched angles between the tapered device and the other component against which the taper device is compressed can usefully be on either face of the tapered device.

Optionally all fluid pathways extending across the wellhead barrier are sealed by tapered sealing devices such as tapered rings, which are optionally compressed between components of the penetrator in order to energise the seal and resist or prevent communication through the pathway. Optionally at least one and optionally both faces of the sealing devices are tapered at angles that do not match the angle against which the sealing devices compressed, so that the mismatch of taper angles highly loads a portion of the sealing device (optionally the outer ends of the sealing devices) thereby enhancing the seal and resisting passage of pressurised fluids through the pathways when the connector has been made up. Optionally, examples of the invention can be constructed which have matching taper angles on the inter- engaging faces of the taper device and (for example) the sleeve, but have

mismatching angles on other faces. Optionally the mismatching of angles reorientates or deforms the tapered device in order to focus the axial force applied by the driving device onto a relatively small portion of the tapered face of the taper device. The various aspects of the present invention can be practiced alone or in

combination with one or more of the other aspects, as will be appreciated by those skilled in the relevant arts. The various aspects of the invention can optionally be provided in combination with one or more of the optional features of the other aspects of the invention. Also, optional features described in relation to one aspect can optionally be combined alone or together with other features in different aspects of the invention. Any subject matter described in this specification can be combined with any other subject matter in the specification to form a novel combination.

Various aspects of the invention will now be described in detail with reference to the accompanying figures. Still other aspects, features, and advantages of the present invention are readily apparent from the entire description thereof, including the figures, which illustrates a number of exemplary aspects and implementations. Any subject matter described in the specification can be combined with any other subject matter in the specification to form a novel combination. The invention is also capable of other and different examples and aspects, and its several details can be modified in various respects, all without departing from the spirit and scope of the present invention. Accordingly, the drawings and descriptions are to be regarded as illustrative in nature, and not as restrictive. Furthermore, the terminology and phraseology used herein is solely used for descriptive purposes and should not be construed as limiting in scope. Language such as "including," "comprising," "having," "containing," or "involving," and variations thereof, is intended to be broad and encompass the subject matter listed thereafter, equivalents, and additional subject matter not recited, and is not intended to exclude other additives, components, integers or steps. Likewise, the term "comprising" is considered synonymous with the terms "including" or "containing" for applicable legal purposes. Any discussion of documents, acts, materials, devices, articles and the like is included in the specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or were common general knowledge in the field relevant to the present invention.

In this disclosure, whenever a composition, an element or a group of elements is preceded with the transitional phrase "comprising", it is understood that we also contemplate the same composition, element or group of elements with transitional phrases "consisting essentially of", "consisting", "selected from the group of consisting of", "including", or "is" preceding the recitation of the composition, element or group of elements and vice versa. In this disclosure, the words

"typically" or "optionally" are to be understood as being intended to indicate optional or non-essential features of the invention which are present in certain examples but which can be omitted in others without departing from the scope of the invention. All numerical values in this disclosure are understood as being modified by "about". All singular forms of elements, or any other components described herein are understood to include plural forms thereof and vice versa. References to directional and positional descriptions such as upper and lower and directions e.g. "up", "down" etc. are to be interpreted by a skilled reader in the context of the examples described and are not to be interpreted as limiting the invention to the literal interpretation of the term, but instead should be as understood by the skilled addressee. In particular, positional references in relation to the well such as "up" will be interpreted to refer to a direction toward the surface, and "down" will be interpreted to refer to a direction away from the surface, whether the well being referred to is a conventional vertical well or a deviated well.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

figure 1 shows a side view of a wellhead penetrator;

figure 2 shows an enlarged view of part of figure 1;

figure 3 shows a sectional view through fig 2;

figure 4 shows a conductor of the figure 1 penetrator; figure 5 shows an alternative conductor of the figure 1 penetrator; figures 6-10 show enlarged views of different parts of figure 4;

figure 11 a, b, c shows enlarged views of seal rings in inactive (in fig lib) and active (in fig 11c) configurations between the ceramic sleeve and a body member of the penetrator of figure 1;

figure 12 a, b & c show enlarged views of seal rings in inactive (in fig 12b) and active (in fig 12c) configurations between the penetrator body member and the penetrator outer housing; and

figure 13 a, b & c show enlarged views of seal rings in inactive (in fig 13b) and active (in fig 13c) configurations between the penetrator outer housing and the wellbore.

DETAILED DESCRIPTION OF CERTAIN EXAMPLES OF THE INVENTION

Referring now to the drawings, a penetrator 1 extending through a wellhead W is used to connect a three-phase cable below the wellhead with a three-phase cable above the barrier of the wellhead. The section through the penetrator 1 shown in figure 3 cuts through one phase of the cable, and passes in front of a 2 ^nd phase of the cable. The 3 ^rd phase of the cable passing through the penetrator is not shown in figure 1, but is essentially the same as the 2 ^nd phase of the cable. All phases of the cable are essentially the same, and hence figure 1 shows the components of the penetrator with the different phases of the cable in both sectional and side views. In some examples, the penetrator 1 passes through an adapter (not shown), which is received within the bore Wb of the wellhead W. The wellhead W is shown schematically in figure 5, but the features of the wellhead W and the adapter will differ in different examples of the invention according to which design of wellhead is used. Certain wellheads will not necessarily need an adapter for utilisation of some examples of the penetrator of the invention, and thus the adapter is an optional feature.

The different phases of the cable require connection across the barrier of the wellhead in order to convey power and signals to and from various devices below the wellhead. The exact nature of the devices which draw power and signals through the penetrator 1 can vary in different examples of the invention, but typical examples of downhole devices that could be connected to power and signal sources above the wellhead could be pumps, tools, etc. Connection of cables across the wellhead causes challenges because the wellhead barrier must typically contain high wellbore temperatures and pressures, and must of course contain the wellbore fluids and prevent uncontrolled leakage of the wellbore fluids out of the well. The temperature and pressure gradients across the wellhead are significant. This is especially the case where steam is injected through the wellhead in order to mobilise heavy oil within a formation and to facilitate its extraction through the well. It is possible for temperature gradients across the wellhead to exceed 300°C.

The different phases of surface and downhole cables on opposite sides of the wellhead W each connect to a respective conductor assembly 10 within the penetrator 1 which forms an electrical connection across the barrier of the wellhead W without compromising the integrity of the barrier of the wellhead W. The conductor assembly 10 is shown in simplified form in figure 4, isolated from the penetrator for the purposes of this figure, but shown in context within the other drawings. The conductor assembly 10 comprises a central conductor 11 optionally in the form of copper or copper chromium bar adapted to transmit electrical power (or optionally signals) between the surface and downhole phases of the cable CI, C2 etc. across the wellhead penetrator. The central conductor 11 optionally has a shoulder 12 extending radially outward from the outer surface of the central conductor 11, which is otherwise shaped as an elongate bar with a long axis. The shoulder 12 is optionally near to the upper end llu of the conductor 11, and can be spaced axially along the conductor 11 a short distance from the upper end llu. The opposite (lower) end 111 of the conductor 11 is optionally externally threaded. The shaft of the conductor 11 below the shoulder 12 is optionally received within the central axial bore of a sleeve 15. The sleeve 15 optionally slides axially over the shaft of the conductor 11, which can be longer than the sleeve 15, thereby allowing the lower threaded end lie of the shaft of the conductor 11 to extend out of the lower end 151 of the sleeve 15, when the upper end of the sleeve approaches the shoulder 12. Before the shaft of the conductor 11 is offered to the bore of the sleeve 15, the shaft of the conductor 11 is passed through the bore of an upper seal ring 19u, which slides over the shaft with clearance between the shaft and the ring 19u, but which is prevented from further travel when it abuts against the shoulder 12 extending radially outwards from the outer surface of the shaft of the conductor 11. Hence, when the shaft of the conductor 11 is passed through the bore of the sleeve 15, and the sleeve 15 is slid axially along the shaft, the upper seal ring 19u is disposed between the lower end of the shoulder 12 and the upper end 15u of the sleeve 15. After the sleeve 15 has been passed over the shaft of the conductor 11, a lower seal ring 151 is passed over the shaft of the conductor 11, and finally the lower externally threaded end 111 of the shaft of the conductor 11 is passed into the internally threaded bore of a driver device in the form of a metallic and conductive connector 18, which is screwed onto the threaded end 111 of the shaft. Driving the connector 18 axially up the threaded lower end 111 of the shaft of the conductor 11 presses the upper end of the connector 18 against the lower end of the lower seal ring 191. This axial force compresses the seal rings 19u, 191 and the sleeve 15 between the lower end of the shoulder 12 and the upper end of the connector 18, and axially tensions the shaft of the conductor 11 between these two points. Figure 5 shows an alternative design of conductor suitable for use in the

arrangement in fig 1, in which the conductor assembly 10' comprises a central conductor 11' as before, but with a threaded section at each end, which mates with internally threaded bores of upper and lower driver devices 18u and 181. Driving the connectors 18u,l axially along the threaded ends of the shaft of the conductor 11' presses the ends of the connectors 18u,l against the ends of the seal rings as previously described, which compresses the seal rings and the sleeve between the driver devices and the conductor 11', and axially tensions the shaft of the conductor 11' between these two points. Otherwise, the function and use of the alternative design of conductor 11' is as described for the other examples, to which the reader is referred for more details. Optionally, the seal rings 19 are formed from a metal, optionally a copper/nickel alloy, but other examples can be formed from steel. One example of a seal ring 19 is formed from Inconel. Typically the material of the seal ring 19 is softer and more malleable than the material of the ceramic sleeve 15, so that it preferentially deforms against the ceramic sleeve 15. Optionally the formation of the seal ring 19 is plastic, i.e. a permanent deformation not subject to recovery when force is removed.

The seal rings 19u and 191 are essentially mirror images of one another in this example, but can optionally have the same profile. As can be best seen in figure 10, the seal ring 191 has a cylindrical external profile and is optionally surrounded by a cylindrical collar 19c which is optionally positioned radially outside the seal ring 191. The internal profile of the seal ring 191 in this example is asymmetric between upper and lower ends of the ring, but symmetric examples could also be used. In this example, the radially innermost face of the ring is a snug fit around the shaft of the conductor 11, but the end faces are tapered. In this example, the lower end face which engages with the upper end of the connector 18 is optionally tapered at the same angle, or substantially the same angle, as the end face of the connector which engages it, but the upper end face 19f of the seal ring is tapered at a different angle as compared with the taper on the end face 15f of the lower end of the sleeve 151 which engages the ring 191. In this example, the taper on the face 19f of the seal ring is closer to parallel than the taper on the face 15f of the sleeve. In this example, the taper on the face 19f is substantially constant along the axial length of the face 19f. A typical taper angle for the face 19f used in this example is between 10 and 30 degrees, for example 20-25 degrees. In this example the taper angle on faces 19f is 21 degrees. The taper angle on the upper end face 18f of the connector 18 can be identical to the taper angle on the mating face 19f, or, as it is in this case, the taper angle of 18f (in this example 20 degrees) can be close to the taper angle 19f. The face 15f has a radius, so the taper angle on the face 15f on the lower end of the sleeve 15 optionally gradually decreases with distance from the end of the sleeve 15, so that at the very end of the tip of the sleeve 15, the taper angle approaches 90° with respect to the axis of the shaft of the conductor 11. However, the taper angle on the face 15f gradually approaches (but optionally does not reach) parallel with respect to the same axis. Therefore, when the tip 19t of the upper end of the seal ring 19 meets the face 15f on the sleeve 15, only the tip 19t is supported radially by the sleeve, and the portion of the seal ring 19 outside the tip 15t of the face 15f is unsupported. At the point on the face 15f where the tip 19t engages the face, the taper angle of the face 15 is optionally greater than the taper angle on the face 19f, for example 21, 22, 23 or 24 degrees. In the present case, the taper angle of the face 15f at the point of engagement with the face 19f is 22 degrees. In other words, the face 15f typically forms an arc, optionally with a non-constant radius, presenting a changing taper angle on the face 15f. The radius of the arc can be constant, or can vary, typically along the axial length of the sleeve. The effect of the axial movement of the seal ring 19 along the face 15f is to urge the tip 19t radially outwards against the inner surface of the collar 19c, compressing the tip radially and axially into the space between the surface 15f and the collar 19c. The collar 19c is substantially resistant to radial extension, and reduces the chances of the tip 19t of the seal ring 191 belling out extensively against the lower end of the ceramic sleeve 15. Since the seal ring 19 is made of softer material than the ceramic sleeve 15, it is squeezed into the tapered area between the surface 15fon the lower end of the sleeve 15, and the inner surface of the collar 19c.

In the present case, the seal ring 19 deforms radially outwards to a small extent and a small section of the inner surface 19f close to the tip 19t forms the seal between the seal ring 191 and the lower end of the sleeve 15. The mismatched taper angles means that all of the axial force exerted by the driving device is transferred through the small surface area, which therefore means that pressure applied (force per unit area) at the sealed area between the seal ring 191 and the sleeve 15 is exceptionally high, and reduces the chances of leaks. At the lower end of the seal ring 191, the taper angle optionally matches the taper angle of the upper surface 18f of the driving device 18. However, the inter-engaging tapered surfaces here can also be mismatched, and in this case, there is typically a 1 degree variance between them. Surface 18f is optionally tapered at 20 degrees, and the engaging lower surface of the seal ring 191 is optionally tapered at 21 degrees in this example, hence the variance between the angles of the inter-engaging surfaces at the upper and lower end of the seal ring 191 can optionally be different, but typically there is a higher variance on the side which engages with the sleeve, thereby focusing more of the force onto the smaller area created by the higher variance, and achieving a higher pressure of seal at these points. A further advantage of the reduced variance in the taper angles between the seal ring 191 and the connector 18 is that the softer material of the connector 18 is not subjected to excessive forces that would tend to deform it, and such forces are focused instead on the seal ring 19.

As the connector 18 is rotated around the axis of the conductor 11, it is driven axially up the threads on the lower end 111 of the shaft of the conductor 11, so that the seal ring 191 is axially compressed between the sleeve 15 and the connector 18, which drives the tip 19t up the tapered face 15f on the sleeve 15. The collar 19c radially outside the seal ring 191 limits the ability of the tip 19t to deform outwardly from the axis of the conductor 11 by flaring, and hence a substantial part of the force generated by the axial movement of the connector 18 up the threads on the lower end of the conductor 111 is concentrated on the relatively small surface area at the interface between the tip 19t of the seal ring 191 and the tapered face 15f on the sleeve. Therefore, since the surface area in contact between the seal ring 191 and the sleeve 15 is relatively small, a substantial pressure can be obtained with relatively minimal force applied through the threaded connector 18. As can be best seen in figure 10, because of the mismatched taper angles between the face 19f and the face 15f, the area of the face 19f that is axially spaced from the tip 19t is unsupported by the tapered face 15f of the sleeve 15, which also enhances the tendency of the seal ring 191 to deform, optionally permanently when subjected to the compression by the axial movement of the driver device 18.

Optionally, the shaft of the conductor 11 has a sheath 13 acting as a primary electrical insulator, which may be formed from a tape comprising polyimide, polytetrafluoroethylene (PTFE) or the like, between the outer surface of the shaft of the conductor 11 and the inner surface of the bore of the sleeve 15. Optionally the sheath 13 extends axially between the seal rings 19u, 191, so that the seal rings engage the conductor 11 direct without engaging the sheath 13. The tape is optionally provided with a high strength and high temperature adhesive. As indicated above, the upper seal ring 19u is optionally (but not necessarily) a mirror image arrangement of the lower seal ring 191, and accordingly, is also compressed between the shoulder 12 at the upper end llu of the shaft of the connector and the upper end of the sleeve 15 in the same way. In the upper seal ring 19u, the collar 19c is optionally omitted, and the seal ring 19u may tend to flare radially outwards more than the lower ring 191 as a result of the axial compression applied by the driver device 18.

Accordingly, as the connector 18 is driven up the threads of the shaft of the conductor 11, the seal rings 19 are driven into contact with the sleeve 15 at each end and are compressed against the sleeve, and the mismatched taper angles highly loads the tips of the rings providing a gas-tight seal and resisting or preventing escape of gas from the bore of the sleeve 15.

In the present example, the tapered faces 19f are optionally coated with a relatively soft but relatively conductive material, for example such as silver or gold or alloys of the same. As the tip 19t is driven axially into contact with the very hard ceramic material on the end of the sleeve 15, the tip 19t and the relatively soft silver surface thereon deforms preferentially (typically permanently) around the hard ceramic material on the end of the sleeve 15 in order to enhance the ability to tension the device without galling the seal rings, and the relatively soft silver surface deforms to accommodate surface imperfections in the seal ring 19 and in the sleeve 15, thereby reducing the gas permeability of the seal even further. Typically the seal rings are formed from a relatively hard metal (alternatively they can be formed from a material that is subsequently treated to harden it), and are optionally adapted to deform permanently when compressed by the driver device onto the harder ceramic sleeve 15 to form a metal: ceramic seal. Optionally, the threads coupling the connector 18 to the shaft of their conductor 11 have a coating of silver or gold (or alloys of the same), optionally in the form of silver loaded epoxy, which decreases the electrical resistivity over the threaded area, and enhances the electrical connection between the connector 18 and the conductor 11. Tightening the threaded connector brings the conductor 11 into high tension thereby ensuring an enhanced electrical contact between the conductor 11 and the connector 18. Optionally, in certain examples, after the conductor 11 has been threaded into the upper socket of the connector 18, the connection is crimped to provide electrical resistance and high pull out strength.

The connector itself is optionally formed from a conductive metal such as copper or copper alloy (e.g. copper cobalt) and optionally is softer than the ceramic material forming the sleeve. The tapered end of the connector engaging the seal ring 191 can optionally be formed with the same taper angle as the lower end of the seal ring 191, so that the compression force from the axial movement of the driver device is transferred more effectively to the seal ring 191 and focussed on the mismatched angles of the engaging faces 15f and 19f. This reduces damage to the softer material of the connector, and increases electrical conductivity between the conductor 11 and the connector 18, which focussing the deformation forces on the interface between the seal ring 191 and the sleeve 15 to cause maximum deformation of the seal ring 19 with the minimum of compression applied by the connector 18.

When the conductor assembly 10 is made up in this manner, the upper end llu of the conductor 11 provides a male connector for cooperation with a socket of a connector above the wellhead W for connection to the surface cable, and the lower end of the connector 18 optionally has a lower socket 18s for cooperation with a male connector of a downhole cable below the wellhead W. Accordingly, the conductor assembly 10 does not provide a fluid pathway for the escape of wellbore fluids contained within the well, but still provides an efficient and effective conduit through the barrier of the wellhead W for power and/or signals without

compromising wellbore barrier functions and containment of wellbore pressure and fluids. In the present example, the sleeve optionally has at least two ribs 16, arranged in axially spaced apart groups. In this example, two groups of ribs 16 are formed on an outer surface of the sleeve 15. The ribs are typically annular, and extend radially outward from the outer surface of the sleeve 15. In this example the ribs 16 are axially spaced from one another, and do not interconnect, leaving a valley between each adjacent pair of ribs 16. The ribs 16 can optionally have a generally rounded profile, and optionally the valleys between adjacent pairs of ribs can be rounded or flat, as best seen in figure 4. The ribs 16 enhance the electrical insulation properties of the sleeve 15 by reducing surface tracking length of electrical current in an axial direction along the sleeve 15. Thus the ribbed sleeve can have a lower surface tracking distance allowing the conductor to be shorter and more compact.

The assembled conductor assembly 10 is then sealed into an inner body 25 of the penetrator which contains a number of axial bores 25b, one bore for each penetrator assembly, and also corresponding to the number of phases of the cable to be connected. In the present example, there are 3 phases of cable to be connected across the wellhead W, and hence the body 25 typically has 3 axial bores, which are optionally radially and circumferentially spaced around the body 25, but which optionally extend parallel to the axis of the wellhead W and of the axis of the connector assembly 10. In order to close the bores 25b and retain the integrity of the wellhead barrier, each conductor assembly 10 is provided with upper and lower seal rings 29u, 291 best shown in figure 11. The seal rings 29 have tapered faces 29f on their inwardly facing end, which bear against the tapered outwardly facing faces 17f of the central shoulder 17 on the connector assembly 10. The tapered faces 29f are set at an angle of 19 degrees. As previously described with respect to the seal rings 19, when the inner and outer surfaces 29i, 29o of the seal ring 29 are parallel to the inner surface 25i of the bore 25b, the faces 29f on the seal rings 29 are tapered at different angles as compared with the faces 17f on the central shoulder 17 of the sleeve 15. The mismatch in the angles is optionally 1 to 2°, and can be seen best in figure 11, although the difference between the start and the tip of the tapered faces is only just perceptible visually. In this example, the taper on surface 17f is optionally steeper than the taper on surface 29f, and in this case, is set at 20 degrees. As can be seen from figures lib and c, the taper angle between an axial outer face 29o of the seal ring 29 and the inner tapered face 29f does not match the angle between the inner surface of the bore 25b and the outer surface 17f of the shoulder 17. Optionally the pocket formed by the inner surface of the bore 25b and the outer tapered surface 17f of the shoulder 17 is formed with a larger angle (in this case, 20 degrees) than the angle between the outer surface 29o and the inner tapered faced 29f. As can be seen by comparing figures lib and c, the tapered faces 17f and 29f initially start off out of alignment with one another, in figure lib, before axial movement of the locking ring 26 and activation of the seals, but after activation, shown in figure 11c, the surfaces 17f and 29f are pressed into parallel alignment, forcing deformation of the distal portion of the tip 29t to a small extent, but also realignment of the outer surface 29o, so that it is non-parallel to the inner surface of the bore 25b when the seals are activated as shown in figure 11c.

Accordingly, although the surfaces 29o and the inner surface of the bore 25b were initially parallel, they are driven into a nonparallel configuration with a mismatched angle in the activated seal by the mismatching of angles on other faces of the seal ring 29. Accordingly, in certain examples of the invention, the effect of mismatched angles on tapered faces can be achieved even where angles on inter-engaging faces are matching. In the example shown in figure 11, the main sealing effect is provided by the radial outward force of the outer surface 29o against the inner surface of the bore 25b at the relatively small area at the tip 29t of the seal ring 29, which is forced into contact with the inner surface of the bore 25b. The greater the compression force exerted on the seal ring 29 by the locking ring 26, the greater the pressure that is applied at the inter-engaging surfaces at the tip 29t.

The bore 25b in the body 25 has an undercut shoulder 25s extending radially into the bore, and facing the lower end of the body 25. The upper seal ring 29u is disposed between this shoulder 25s and the upper tapered face 17f on the shoulder 17. The lower seal ring 291 is disposed between the lower tapered face 17f and a lock ring 26 which has external thread on its outer surface, which cooperate with an internal threads on the lower part of the bore 25b, below the shoulder 25s. Accordingly, after the seal rings 291, 29u have been placed over the sleeve 15, the conductor assembly 10 is offered to the bore 25b from the lower end, and the lock ring 26 is then screwed down into the threads on the inner surface of the bore 25b, to compress the seal rings 2 against the hard ceramic shoulder 17 and energise the seals. The mismatch on the taper angle is between the seal rings 29 and the shoulder 17 concentrate the loading area near to the apex of the shoulder 17, providing a high contact force at the interface between the surface 17f and the surface 29f, producing a gas tight seal and preventing or restricting the escape of pressurised fluids from the bore 25b. The principle of operation of the seal rings 29 is similar to that of the seal rings 19, and similar features can be shared and combined between the rings 29, 19. However, in addition to sealing between the surfaces 17f and 29f, the seal rings 29 also seal against the inner surface of the bore 25b, as is best seen in figure 11c. The compression force exerted by the lock ring 26 drives each of the seal rings 29 up the tapered faces 17f of the shoulder 17 on the sleeve 15, thereby localising the engagement between the seal ring 29 and the sleeve 15 (on the inside) and between the seal ring 29 and the bore 25b of the body 25 (on the outside) to the small areas of contact adjacent to the tip 29t of the seal rings 29. Thus, the small contact area between the seal rings 29, the sleeve 15 and the bore 25b permits the same high pressure seal using only the force applied by the lock ring 26. The reader is referred to previous description relating to the seal rings 19 for optional features that can be used for the seal rings 29. In particular, the seal rings 19, 29 can optionally be formed from metal, and can optionally be adapted to deform permanently against the harder ceramic material of the sleeve 15 upon assembly. Seal rings 19, 29 are optionally silver plated to accommodate surface imperfections in either surface 2 thereby achieve a better gas tight seal. Silver or gold plating can optionally be applied to the lock ring 26 in addition to the seal rings 19, 29. This can offer a low friction coating to allow application of a high torque when tightening the various components, and the relatively soft silver or gold surface also deforms, compensating for surface imperfections to improve the containment of fluids. After assembly of the conductor assembly 10 into the body 25, the correct downhole phase of the cable is connected with the lower socket 18s on the connector 18, and is threaded into the socket and then optionally crimped to provide electrical resistance and high pull out strength. After a secure connection has been made to the downhole phase of the cable, and after other phases of the downhole cable have been similarly connected to other conductor assemblies 10 passing through the body 25, the different connections can be tested and corrections made if necessary at this point. The upper end of the cable and penetrator body 25 is then optionally secured in the central bore of a penetrator outer housing H, and the lower end is then secured in position by at least one layer of adhesive such as epoxy, optionally with high-strength and high temperature resistance profiles. Optionally, in some examples, the outer (lower) layer of the housing H can be filled with a 2 ^nd layer of epoxy, optionally having a different (for example higher) temperature resistance profile, but possibly a weaker pull out strength as a cap to seal the lower end of the housing H. When thus assembled, the lower end of the housing H with the phases of the downhole cable extending from it renders the penetrator 1 relatively resistant to chemical attack, and to thermal degradation from heat build-up within the wellhead W. Optionally the body 25 can be secured in the bore of a hanger (not shown) before being inserted into the bore of the housing H.

With reference to fig 12, the body 25 is optionally secured in place within the bore of the penetrator housing H by upper and lower tapered devices 39u, 391, which can have mismatched tapers as previously described. The lower tapered device supporting the body 25 from beneath, is provided by the tapered seal ring 3 1, which as shown best in figure 12a, engages the tapered lower surface 25f on the underside of the radially extending shoulder on the body 25, and which is prevented from axial downward movement within the bore of the wellhead W by means of the radially inward extending shoulder Hs. The upper tapered device is provided by the upper seal ring 39u, which engages the upper tapered surface 25f on the upper side of the body 25, and which is compressed into position by a driver device in the form of a lock ring 32, having external threads which engage with internal threads on the bore of the wellhead W, allowing the lock ring 32 to be screwed down into the bore of the housing H, to compress the tapered devices 3 u,l against the tapered surfaces 25f of the body 25. The principle of operation of the seal ring 39 and the upper tapered surface on the hanger 30 is similar to that of the seal rings 29, and similar features can be shared and combined between the rings 29, 19. However, as with the seal 29 between the sleeve 15 and the body 25, in addition to sealing between the surfaces 25f, the seal rings 29 also seal against the inner surface of the bore 25b, as is best seen in figure 11c. The compression force exerted by the lock ring 26 drives each of the seal rings 29 axially along the tapered faces 17f of the shoulder 17 on the sleeve 15, thereby localising the engagement between the seal ring 29 and the sleeve 15 (on the inside) and between the seal ring 29 and the bore 25b of the body 25 (on the outside) to the small areas of contact adjacent to the tip 29t of the seal rings 29. Thus, the small contact area between the seal rings 29, the sleeve 15 and the bore 25b permits the same high pressure seal using only the force applied by the lock ring 26. The reader is referred to previous description relating to the seal rings 29 for optional features that can be used for the seal rings 39. As can be seen in the close-up view of figure 12b and c, the tapered surfaces 25f, 39f have mismatching angles, optionally differing by 1 or 2°, which results in the tapered surfaces permanently deforming and/ or realigning at the tips and focusing the compressive load applied by the lock ring 32 on this relatively small surface area, thereby enhancing the gas tight seal. As with previous seal rings, the lock rings and seal rings can be coated with a softer compound such as silver or gold, which is adapted to deform in order to compensate for surface irregularities, and to reduce friction between the components and resist galling. Once assembled in place within the bore of the housing H, the penetrator body 25 can be cemented in position within the housing by a layer of epoxy filling the internal space within the housing H and the outer armour layer of the downhole cable. Suitable tapes and epoxy resins will be known to the skilled person and can be utilised within the scope of the present invention. Instead of tapes, heat shrink sleeves can be used. The upper end of the conductor 11 emerging from the wellhead W is optionally insulated with a high temperature electrically insulating copolymer sleeve which is optionally retained by the upper end of the penetrator body 25 at its lower end by means of a bulb lip allowing a degree of expansion and contraction, and which has a separate sleeve at its upper end for each conductor emerging from the wellhead W. Each conductor is optionally provided with a cap 28, which optionally covers a portion of the shaft of the conductor 11 above the shoulder 12, and the interface between the shoulder 12, seal ring 19u and the sleeve 15. The cap 28 is optionally formed from a temperature resistant insulator, optionally a plastics material, such as solid sintered and machined polyimide, which optionally provides a further layer of electrical insulation, and reduces the required thickness of the copolymer sleeve. The sleeve and the 28 provide a compression seal to stop surface tracking and a moisture barrier for the internal electrical contacts. The upper end of the conductor 11 is optionally connected to the surface cable 3 via an Inconel connector (optionally rated to 400°C). The connector can optionally be housed within temperature resistant sleeves above the wellhead W provided with external fins to assist escape of any heat built up within the penetrator 1 the sleeves can be formed from materials with relatively low thermal conductivity, for example stainless steel 316, which reduces the transmission of heat energy from the surrounding environment into the cables within the sleeves. The voids within the sleeves can be filled with epoxy having a low thermal conductivity, and serving the same purpose. The housing H is optionally secured in place within the bore of the adaptor or in the bore of the wellhead W by upper and lower tapered devices, which optionally have mismatched tapers as previously described. The lower tapered device supporting the housing H from beneath is provided by the tapered upper surface 49f of a lower seal ring 491, which engages a tapered lower surface on a radial shoulder of the housing H, and which is prevented from axial downward movement within the bore of the wellhead W by means of a radially inward extending shoulder of the wellhead or of the adapter device if present. The upper tapered device is provided by a seal ring 49u, which engages the upper tapered surface on the upper side of the shoulder on the housing H, and which is compressed into position by a driver device in the form of a lock ring 42, having external threads which engage with internal threads on the bore of the wellhead W, allowing the lock ring 42 to be screwed down into the bore of the adapter A, to compress the tapered devices 49 against the tapered surfaces of the shoulder on the housing H. The principle of operation of the seal rings 49 and the tapered surfaces on the shoulder on the housing H is similar to that of the seal rings 19, 29, & 39 and similar features can be shared and combined between the rings 49, 39, 29 & 19. The reader is referred to previous description relating to the seal rings 19, 29 and 39 for optional features that can be used for the seal rings 49. In particular, at least one of the surfaces of the shoulder on the housing H and the seal rings 49 have mismatching angles, optionally differing by 1 or 2°, which results in the tapered rings 49u, 491 permanently deforming at the tips and focusing the compressive load applied by the lock ring 42 on this relatively small surface area, thereby enhancing the gas tight seal across the barrier of the wellhead. As with previous seal rings, the lock rings and seal rings can be metallic, and can be coated with a softer compound such as silver or gold, which is adapted to deform in order to compensate for surface irregularities, and to reduce friction between the components and resist galling, while providing a metal to metal seal which is highly temperature resistant.

Accordingly, the housing H is optionally secured within the bore passing through the wellbore adapter A with tapered seal rings as previously described for other bores, and once compression is applied to the seal rings, they optionally deform as previously described, in order to provide a gas tight seal across the wellbore barrier. The wellbore adapter may seal within the bore of the wellbore body in the same manner, or by a different mechanism.