GB2378916A

GB2378916A - A heatable conduit

Info

Publication number: GB2378916A
Application number: GB0214260A
Authority: GB
Inventors: Philip Head
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-06-20
Filing date: 2002-06-20
Publication date: 2003-02-26
Also published as: GB0214260D0; WO2002104074A1

Abstract

A conduit is formed for use in the production of oil or gas, the conduit including an inner tube 120 and an outer tube 126 coaxial with the inner tube 120. A heating element, preferably consisting of power strips 124 and heating strips 125, is secured to the outer surface of the inner tube 120, and the outer tube 126 applied to the inner tube and heating element by extrusion. The inner tube is formed as an extrudate. The heating element has a substantially longitudinal planar form, and is wrapped upon the inner tube. A gas impermeable layer is formed on the outer tube by wrapping one or more substantially planar longitudinal gas impermeable sheets around the outer tube. A cable or conduit may be fed through an extruder to form a first layer of extrudate substantially encompassing the cable or conduit and an impermeable tube may be applied around the cable or conduit. Ends of protected cable may be connected to a termination assembly (170) (figure 16 - not shown). Protected cable may be installed in a riser. Two lengths of protected tube may be joined together by welding.

Description

237891 6

Tubing System This invention relates to tubing and conduit systems, particularly but not exclusively in sub-sea and sub-surface environments, for the production of 5 oil and gas and associated tasks.

Conductor systems such as arrnoured cables are much used in the drilling of boreholes and the subsequent production of oil, both to supply power and to transmit signals. The conditions that such conductor systems 10 encounter are harsh; cabling may be subjected to the high pressures of the well fluid, mechanical stresses from being pulled upon or compressed by surrounding components, and high temperatures.

Other types of line that may be used in these environments, such as 15 hydraulic and fibre optic lines, must be designed with the same considerations in mind.

Known armoured cable is typically formed by wrapping multiple layers of different material around the conductors or piping to be protected. The 20 complex production process results in armoured cable being relatively expensive. A major problem identified with existing power cables is that gas migrates into the conductor; some gas, such as hydrogen sulphide, is highly 2S corrosive to the copper typically used for conductors. Also, the gas permeates slowly under high pressure. If the cable suddenly decompressed (for example

a seal or a pump fails) the gas in the cable expands and can cause the cable to explode. It is an object of the present invention to provide a reliable conductor or 5 conduit system that is convenient to manufacture. Other objects of the invention will become apparent from time to time in the description.

According to the present invention there is provided a method of forming a conduit for the production of oil or gas, the conduit including an 10 inner tube and an outer tube coaxial with the inner tube, including the steps of securing a heating element to the outer surface of the inner tube and applying the outer tube to the inner tube and heating element by extrusion.

Preferably the inner tube is formed as an extrudate.

Preferably the heating element has a substantially longitudinal planar form, and is wrapped upon the inner tube. Preferably a gas impermeable layer is formed on the outer tube by wrapping one or more substantially planar longitudinal gas impermeable sheets around the outer tube.

According to another aspect of the present invention there is provided a conduit as herein defined.

According to another aspect of the present invention there is provided a 25 method of forming a protected cable or conduit, comprising the steps of feeding the cable or conduit through an extruder to form a first layer of

r extrudate substantially encompassing the cable or conduit, and applying a impermeable tube around the cable or conduit.

Preferably the impermeable tube is applied around the cable or conduit 5 and the first layer of extrudate.

According to another aspect of the present invention there is provided a protected cable as herein defined.

10 It will be seen that the above processes can conveniently incorporate an impermeable layers and/or heating elements to protect the power lines, conduits and other components from contamination by fluid or gas.

The invention will now be described, by way of example, reference 15 being made to the accompanying drawings, in which: Figures 1 to 6 are cross sectional views of the manufacture of the protected tube; 20 Figure 7 shows a plan view of a power and heating layer; Figure 8 shows a plan view of another embodiment of a power and heating layer; 25 Figure 9 shows a plan view of another embodiment of a power and heating layer;

Figure 10 shows a view of a power and heating layer applied to part of the protected tube; 5 Figure 11 shows a view of the protected tube in use; Figure 12 shows a longitudinal view of the protected tube in a riser or casing; Figure 13 shows a longitudinal view of another embodiment of the protected 10 tube in a riser or casing; Figures 14 and 15 show diagrammatic views of the manufacture of the protected tube; 15 Figure 16 shows a longitudinal sectional view of a termination of the protected tube; Figure 17 shows a longitudinal sectional view of another embodiment of a termination of the protected tube; Figure 18 shows a longitudinal sectional view of the joining of two ends of protected tube; Figures 19 and 20 show longitudinal sectional views of another embodiment of 25 the joining of two ends of protected tube;

Figure 21 shows a longitudinal sectional view of a termination of the protected tube in a riser or casing; Figure 22 shows a longitudinal sectional view of another embodiment of a 5 termination of the protected tube in a riser or casing; Figure 23 shows a longitudinal sectional view of another embodiment the protected tube in a riser or casing; 10 Figure 24 shows a longitudinal sectional view of another embodiment the protected tube; Referring to figures 1 to 6, a steel tube 120 is coated in adhesive 122, to which is affixed two power strips 124 and a line of heating strips 125. After 15 the power strips 124 and heating strips 125 have been applied, the outer surface of the tube is coated in a plastic layer 126. Ideally, this plastic layer 126 is applied by passing the steel tube and heating and power strips through a die, the plastic layer being extruded around the steel tube. A layer 128 of aluminium is applied over the plastic layer 126 to form a gas impermeable 20 barrier, and a further layer of plastic is applied over the aluminium, to protect the aluminium layer and for handling purposes. This plastic coating improves the handling qualities of the cable, it could have surface roughness added or profile changes to assist gripping.

25 The aluminium layer may be provided as a reeled strip, being unwound as the steel tube and heating means are exiting the extrusion station. The

aluminium strip is formed around the layer of extrudate, and swayed so that it fits reasonably tightly with the extrudate layer. The seam of the aluminium may be welded. The aluminium could also be applied from more than one strip, which will result in more than one seam, again these seams are preferably 5 welded to form an impermeable metal layer.

Referring to figure 7, two lines of heating pads 125 are disposed along a strip of plastic film 135. A major positive rail 221 and a major negative rail 222 are also disposed along the plastic strip 135, the major negative rail 222 10 situated between the two lines of heating pads. Each heating pad 125 comprises an area of conductive carbon ink. Along each long side of each heating pad runs a minor positive rail 224 and a minor negative rail 223.

Conductive connection members 225 connect the minor positive and negative rails 224, 223 to the respective major positive and negative rails 221, 222. It IS will be seen that one set of the minor positive rails, on the outer edge of the plastic strip, cannot be connected in this way. Where the plastic strip is to made into a tube, connection members may be provided on the major positive rail 224 so that the connection members overlap the seam, connecting the minor positive rails. Alternatively (where the plastic strip is to be applied in a 20 different manner as described below), insulated flying leads may connect these minor positive rails to the major positive rail. When the major positive and negative rails 221, 222 are held at a potential difference, that potential difference is applied across the heating pads, causing them to heat up as current flows through them. The plastic film 135 with the rails and heating 25 pads are applied on the protected tube in a manner described below.

r Referring to figure 8, the heating strips 125 may be disposed in a single line between two power lines 124. A voltage is applied across each heating strip via flying leads 130 from the power strips, the power strips 124 being held at a potential difference. The strips include a thermostat 132 and 5 processor unit 133 which controls the operation of the heating strip so that a constant temperature may be maintained. The thermostat and processor unit may also include other sensors, such as pressure sensors, accelerometers etc., each processor then superimposing the collected data onto the power lines so that the multiplexed signals may be picked up at a subsurface location or 10 floating vessel as appropriate. Again the power strips 124, heating strips 125 and flying leads 130 are disposed in a planar fashion upon a strip of plastic film 135, so that the power strips and heating strips may be conveniently applied to the steel tube.

15 Referring to figure 9, a heating element may be formed using a convoluted configuration of resistive wiring 137 connected between the two power lines 124 via processor/thermostats 131. Typically each such restive heating section is between 1 and SO melees long.

20 Referring to figure 10, the film 135 is wrapped upon the steel tube in a helical fashion, the heating strips and power strips thus each forming helices.

Referring to figure 11, the protected tube may be installed in a well bore 141, or could be used to convey oil along a riser 149 from a well head 142 to a 25 central connection node 143 or to a floating vessel 144 or the like. The oil's viscosity is maintained, particularly when the pipe is running through cold

water, and the sensors are particularly useful for gathering well bore data, but data can also be gathered from the protected tube laying along the surface of the sea bed.

5 Referring to figure 12, the protected tube 150 may be installed in a riser or a well casing 140, and either secured by swaying internally, or left to hang from a cable 146 and cable head unit 145. The cable head unit includes apertures 147 suitable for allowing oil to flow through the through bore of the tube. The cable also supplies power to the power strips. Equally, power could 1Q be supplied from a 'stab in' assembly 148 at the bottorr of the protected tube, shown in figure 12.

The aluminium layer protects the heating strip, power lines and sensors from corrosion. As in the previous embodiments, the aluminium layer also 15 minimises the risk of gas permeating the structure of the tube to lead to explosive decompression.

Referring to figure 14 and 15, the outer layer of extrudate may include or comprise a material having a low thermal conductivity, that is, a heat 20 insulator. Figure 15 shows flat lengths of pipe 154 (the joining of the individual lengths of pipe will be described below) having a coating film 156 applied to them from a reel 158, the lengths of pipe then passing through a polyurethane coating station 160, where polyurethane is extruded around the protected tube to form an insulating layer. The polyurethane coated protected 25 tube 165is then wound upon a reel 162 for storage. Referring to figure 15, the protected tube 155 may alternatively be manufactured as a complete length,

r stored upon a reel 157, and unreeled through the polyurethane coating station 160, before again being reeled 162 for storage and transportation. When the protected tube is to be disposed, it may be plastically unreeled and injected in a similar fashion to coiled tubing.

Referring to figure 16, one or both ends of the protected cable may be connected to a termination assembly 170, the inner steel tube 120 extending into the termination assembly 170 and sealed against an o-ring 172. The heating and power layer 123 is exposed at the end of the protected tube 100, lO and one or more pins 174 extend through the wall of the termination assembly 170 to contact the power rails of the heating and power layer 123, power for the heating elements thus being provided through these pins 174. In this embodiment, a flexible pressure member 176 and flexible tress member 178 are applied after the application of the heating and power layer, to provide the 15 protected tube with strength and flexibility. The resilience of these layers urges outer layers radially outwards, to that the outer metal impermeable layer and the polyurethane layer 175 are urged against the mouth 179 of the termination assembly to create a good seal. The stress member layer 178 is bent back into an annular cavity 181 of the termination assembly, helping the 20 securement of the protected tube lOO.

It will be noted in particular that an outer layer of metal, or indeed other flexible materials capable of withstanding high stress, can be substituted for the aluminium layer to form a flexible stress member for the protected tube.

Referring to figure 17, the termination assembly may simply include a pair of o-rings, a first o-ring 172 sealing against the steel tube as before, and a second o-ring sealing 173 against the outer insulation layer 175. In each case, the termination assembly includes a bore 171 to continue the bore of the 5 protected tube, and a flange for securement of the termination assembly.

To join two lengths of protected tube together, the steel tube 120 is exposed at the ends of the protected tubes 100 to be joined, as shown in figure 18. An annular compression fitting member 190 is introduced into each 10 protected babe end. The exposed steel tube is introduced into a fitting collar 192, which is welded to the aluminium layer i28 protected tube to seal the collar. The fitting collars 192 extend beyond the end ofthe steel tube 120, and are brought to an abutting position and welded together. The fitting collars 192 are then securely attached to the protected tube 100 by swaying the outside 15 of the fitting collars above the annular compression fitting member 190, so that the a secure seal and bond is made between the steel tube and fitting collar in regions 194.

It will be seen that in this type of splicing, the power lines of one 20 protected tube do not connect with the other, although since the heating elements are powered between rails extending along the length, each tube may be separately powered from the ends opposite the splicing site. Referring to figures 19 and 20, if it is desired to though to have the each protected tube's power lines connected, the end of each protected tube 100 is prepared so that 25 the power and heating layer 123 extends over the end of the steel tube 120. An internal liner 196 is included between the two annular compression fitting

members 192, the internal liner 196 including conductive strips to electrically connect the two power lines 124 of one protected tube 100 to the corresponding two power lines of the other protected tube 100 (figure 19 shows the protected tube joint without the internal liner in order that the power 5 lines may be seen). An internal swaying die is then introduced into the bore of the of the protected tubes 100, and used to internally swage the internal liner to create a good connection between the internal liner 196 and the protected tubes' power lines 124.

10 The termination assembly shown in figure 16 may be conveniently used in order to utilise the protected tube as a riser having integral heating capability. Referring to figure 21, a termination assembly 170 similar to that shown in figure 16 may be employed to hang the protected tube 100 in a riser to serve as a liner for the riser (as described and illustrated in figure 12). In the 15 inner surface of the well hanger unit 145 two slip rings 200, 201 lead, via a plug 174, to the electric power cable associated with the tensile cable 146 upon which the protected tube 100 is lowered. The end of the protected tube is exposed as for the termination assembly shown in figure 16, but a profiled end member 204 is attached to the protected tube lOO, this end member including 20 to slip rings 202, 203 corresponding to the slip rings 200, 201 of the hanger unit 145. Alternatively, the power may be supplied through the riser or casing 140, the hanger unit 145 and cable 146 only being used to lower and/or install the protected tube liner 100.

25 Referring to figure 22, alternatively or additionally, a termination assembly may be employed at the bottom end of the protected tube when

acting as a liner in a riser, (as described and illustrated in figure 13). At the bottom of the riser, a termination assembly 148 includes a plug 174 connected to a power supply, the plug being connected to two split rings 200. 201 on the inner surface of the termination assembly. The end of the protected tube is 5 exposed as for the termination assembly shown in figure 17, but a profiled end member 204 is attached to the protected tube 100, this end member including two slip rings 202. 203 corresponding to the slip rings 200, 201 of the termination assembly 148. Upon the protected tube liner 100 being lowered to the termination assembly, the profiled end member 204 stabs in to the 10 termination assembly 148, to supply power to power lines in the protected tube. Equally, the hanger and the stab-in systems could be combined so that the power lines in the protected tube, supplied through the hanger unit, 15 supplies power to some down hole apparatus via the stab-in assembly.

Referring to figure 23, the diameter of the protected tube 100 may be sufficiently small compared to that of a riser 140 so that an annulus 220 exists between the protected tube 100 and the riser 140. Here, the protected tube is 20 attached to a hanger unit 246 which is supported upon a shoulder 244 on the inner surface of the riser 140. A power cable 243 outside of the riser extends through the riser to two split rings 230, 231 on the inner surface of the riser, which contact two split rings 234, 235 on the inner surface of the hanger unit 246. The protected tube is connected in a manner as previously described so 25 that the power lines of the power and heating layer of the protected tube are supplied with power. The hanger unit 246 is provided with ports (which may

operated by valves) through which the annulus 220 between the protected tube 100 and the riser 140 on the one hand, and the riser bore above the hanger unit 246 on the other, can communicate. In this embodiment, viscous oil produced along the annulus is heated by the protected tube 100 and so kept fluid.

Referring to figure 24, a pipeline 250 may become clogged with oil if the temperature of the oil is low enough to become very viscous. To unplug the pipeline, a drill bit 252, powered by an electric motor 254, and including a traction tool 256 and booster pump 258, is introduced into the pipeline 250 10 towing a protected tube 100 (the protected tube may though have enough rigidity be pushed behind the drill bit, or even to supply weight on bit). The drill bit 252 cuts up any solidified oil as it passes through the pipeline 250, and the oil then passes through into the heated protected tube, where the oil is heated to reduce its viscosity. The electric motor 254 for the drill bit 252 is 15 supplied from the power lines of the protected tube lOO. When the drill assembly, that is, the drill bit 252, electric motor 254, traction tool 256 and booster pump 258, emerges from the end of the pipeline, it may be detached from the protected tube 100, which is left in the pipeline 250 to supply heat to ensure that the oil remains fluid, as shown in figure 25.

It will be appreciated that particular features described in one embodiment may be transposed with equivalent features used in other embodiments. For example, any of the methods of securing the impermeable metal sheet may be applied to the conduit.

It will also be appreciated that other material and components could be used with equivalent effect. For instance, metals other than steel and aluminium could be used as cylindrical barriers.

Claims

1. A method of forming a conduit for use in the production of oil or gas, 5 the conduit including an inner tube and an outer tube coaxial with the inner tube, including the steps of securing a heating element to the outer surface of the inner tube and applying the outer tube to the inner tube and heating element by extrusion.

10

2. A method according to claim 1 wherein the inner tube is formed as an extrudate.

3. A method according to any previous claim wherein the heating element has a substantially longitudinal planar form, and is wrapped upon the inner 1 5 tube.

4. A method according to any previous claim wherein a gas impermeable layer is formed on the outer tube by wrapping one or more substantially planar longitudinal gas impermeable sheets around the outer tube.

5. A conduit according to any of claims 1 to 4.

6. A method of forming a protected cable or conduit, comprising the steps of feeding the cable or conduit through an extruder to form a first layer of 25 extrudate substantially encompassing the cable or conduit, and applying a impermeable tube around the cable or conduit.

7. A method according to claim 6, wherein the impermeable tube is applied around the cable or conduit and the first layer of extrudate.

5

8. A method according to claim 6, wherein the first layer of extrudate is applied around the cable or conduit and the impermeable tube.

9. A method according to any of claims 6 to 9, wherein the impermeable tube, cable or conduit and the first layer of extrudate is fed through a second 10 extruder to fornn a second layer of extrudate substantially encompassing the cable or conduit, first layer of extrudate and impermeable tube.

10. A method according to claim 9 when dependent upon claim 7, wherein a layer of heat shielding material is applied to the first layer of extrudate, and 15 the impermeable tube is secured by the application of heat.

11. A method according any of claims 6 to 10 wherein the one or more conductors or cables are inserted into the extrudate.

20

12. A method according to any of claims 6 to 11, wherein the extrudate has a texture applied.

13. A protected cable or conduit according to any previous claim.

14. A method of connecting a cable or conduit according to any previous claim where the outer layer of extrudate is stripped to reveal the impermeable layer. 5

15. A method as herein described and illustrated.

16. A protected cable or conduit as herein described and illustrated.

17. Any novel and inventive feature or combination of features specifically 10 disclosed herein within the meaning of Article 4H of the International Convention (Paris Convention).