Technical Field of the Invention

The present invention relates to a coupling for insulated heating cables for use in the oil and gas industry. In particular, the present invention relates to an integral coupling for joining together the core of a heating section of a mineral insulated heating cable and the core of a non-heating (or cold) section of a mineral insulated heating cable.

Background to the Invention

Thermal enhanced oil recovery involves heating hydrocarbon material such as heavy oil in a reservoir to reduce the viscosity of the material and allow it to be more easily extracted. Enhanced oil recovery can improve recovery from a reservoir by around 30% to 60%.

Insulated heating cables are used as a means to heat hydrocarbon material. Such cables usually comprise a heating section and a non-heating section. The heating section is placed in the vicinity of a reservoir and converts electricity into heat to supply heat to the reservoir and increase the temperature of the trapped hydrocarbon material. The non- heating section is typically much longer than the heating section and transmits electricity from a source to the heating section.

Each of the sections comprises a central metal core surrounded by insulation (typically magnesium oxide), and is covered in a metal sheath (typically stainless steel). The metal core of the heating section is typically a copper-nickel alloy, which heats up as electricity passes through it, whilst the core of the non-heating section is typically mostly copper, which efficiently transmits electricity. Since the heating section core and the non- heating section core are separate components, the first step of assembling an insulated heating cable is to connect the two cores together.

Accordingly, conventional heating section cores and non-heating section cores are each formed with an end portion having a flat surface. The heating section core and the non-heating section core are coupled together by welding these flat surfaces together, which forms an integral splice within the finished cable.

Embodiments of the present invention seek to provide an improved coupling between a heating section core and a non-heating section core of an insulated heating cable. Summary of the Invention

According to a first aspect of the invention, there is provided a coupling between a heating section core and a non-heating section core of an insulated heating cable, the coupling comprising: a heating section core end portion provided on the heating section core; and a non- heating section core end portion provided on the non-heating section core, wherein the heating section core end portion and/or the non- heating section core end portion are engageable with one another.

In this way, the present invention provides an integral coupling for a mineral insulated heating cable in which the heating section core and the non-heating section core can securely engage with one another to couple the heating section core and the non- heating section core together. This locked arrangement provides increased mechanical strength across the splice between the two cores and allows the cores to be held tightly together in alignment prior to being welded to one another, for example by cold welding during a cable compaction and cold working roll reduction stage, which results in an improved electrical connection between the cores. The improved electrical connection increases the efficiency of electricity transmission from the non-heating section core to the heating section core, which leads to an environmental benefit. The present invention is in contrast to conventional couplings, in which the non-heating section core and heating section core simply abut with one another as described above.

The heating section core end portion may engage with the non-heating section core end portion. Alternatively, the non-heating section core end portion may engage with the heating section core end portion.

The heating section core end portion and/or the non-heating section core end portion may be releasably engageable with one another. In particular, the heating section core end portion and/or the non- heating section core end portion may be releasably engageable with one another prior to a cold working roll reduction stage. The heating section core end portion and the non- heating section core end portion may be welded to one another in addition to being engaged to one another. In particular, the heating section core end portion and the non-heating section core end portion may be cold welded to one another in addition to being engaged to one another.

The heating section core end portion may be an integral part of the heating section core. Alternatively, the heating section core end portion may be a part attached to, or formed on, the heating section core. The non-heating section core end portion may be an integral part of the non-heating section core. Alternatively, the non-heating section core end portion may be a part attached to, or formed on, the non-heating section core. At least one of the end portions may comprise a male element. The male element may be formed on, or integral to, an end face of the end portion. The male element may be substantially cylindrical. The male element may be substantially cone shaped.

At least one of the end portions may comprise a female element. The female element may be formed in, or integral to, an end face of the end portion. The female element may be substantially cylindrical. The female element may be substantially cone shaped.

For example, a male element may be provided on the heating section core end portion and may be inserted into, and received by, a female element provided on the non- heating section core end portion. Alternatively, a male element may be provided on the non-heating section core end portion may be inserted into, and received by, a female element provided on the heating section core end portion. Thus, the heating section core end portion and/or the non- heating section core end portion may be engageable together by mating with one another. The male element may comprise a protuberance that protrudes from an end face of an end portion. The female element may comprise a bore cut into an end face an end portion.

The male element and the female element may have substantially the same diameter. The male element and the female element may have substantially the same length. The male element and the female element be engageable with one another in an interference fit or a friction fit.

The male element may have a male screw thread formed on an outside circumferential surface. The female element may have a female screw thread formed on an inside circumferential surface. The male element and the female element may be engageable with one another in a screw fit.

According to a second aspect of the invention, there is provided an insulated heater cable comprising a coupling according to the first aspect of the invention. In particular, the insulated heating cable may be a mineral insulated heating cable for use in, for example, thermal enhanced oil recovery in the oil and gas industry.

According to a third aspect of the invention, there is provided a method of coupling a heating section core and a non-heating section core of an insulated heating cable together, the method comprising the steps of: providing a heating section core end portion on the heating section core; providing a non- heating section core end portion on the non-heating section core; wherein the heating section core end portion and/or the non- heating section core end portion are adapted so that they are engageable with one another and the method further comprises the step of engaging the heating section core end portion and the non- heating section core end portion together to secure the heating section core and the non- heating section core together.

The third aspect of the first aspect of the invention may comprise any or all features of the first aspect of the invention.

In particular, the method may comprise the step of: welding the heating section core end portion and the non-heating section core end portion to one another.

The step of welding the heating section core end portion and the non- heating section core end portion to one another may comprise cold welding the heating section core end portion and the non-heating section core end portion to one another by passing the coupling through a roll reduction mill. Detailed Description of the Invention

In order that the invention may be more clearly understood embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, of which:

Figure 1 is a perspective view of a coupling according to an embodiment of the invention, with the heating section core separated from the non-heating section core;

Figure 2 is a side view of the coupling shown in Figure 1 , with the heating section core separated from the non-heating section core;

Figure 3 is a side view of the coupling shown in Figure 1 , with the heating section core fully engaged with the non-heating section core;

Figure 4 is a cross section view of the coupling shown in Figure 3, with the cross section taken along the longitudinal axis of the coupling;

Figure 5 is a cross section view of a mineral insulated heating cable according to an embodiment of the invention, which incorporates the coupling shown in Figures 1 to 4, with the heating section core fully engaged with the non-heating section core; and

Figure 6 is a cross section of the mineral insulated heating cable shown in Figure 5 during compaction and cold working when passing through a roll reduction mill. Figures 1 to 4 illustrate a coupling 1 between a heating section core 2 and a non- heating section core 3 of an insulated heating cable.

The heating section core 2 and the non-heating section core 3 are each substantially cylindrical metal rods. The heating section core 2 is formed from a copper-nickel alloy which is selected so that the temperature of the heating section core 2 increases as electricity flows through it. Thus, the heating section core 2 effectively acts as a heating element.

The heating section core 2 has a heating section core end portion 10 at one end. The heating section core end portion 10 comprises an engagement means, which in this embodiment is a substantially cylindrical male element 9 in the form of a substantially cylindrical protuberance protruding from an end face 7 of the heating core end portion 10. A male screw thread is formed on the outside surface of the male element 9.

The non-heating section core 3 is formed mostly from copper and serves to transmit electricity from a source to the heating section core 2. The non- heating section core 3 has a non- heating section core end portion 4 at one end. The non-heating section core end portion 4 comprises an engagement means, which in this embodiment is a female element 5 in the form of a substantially cylindrical bore in an end face 6 of the non-heating section core end portion 4. A female screw thread is formed on the inside surface of the female element 5, which can cooperate with the male screw thread formed on the outside surface of the male element 9 so that the male element 9 can engage with the female element 5.

The male element 9 protuberance and the female element 5 bore are each formed with similar diameters and lengths. In use, the heating section core 2 and non- heating section core 3 are joined together by the coupling 1. In particular, the male element 9 is inserted into the female element 5 and is rotated so that the male screw thread on the outside surface of the male element 9 engages with the cooperating female screw thread on the inside surface of the female element 5. Thus, the heating section core 2 mates with the non- heating section core 3. The male element 9 is rotated until the heating section 2 becomes fully engaged with the non-heating section 3, where the end faces 6, 7 are adjacent one another. Indeed, in this embodiment, the end faces 6, 7 are abutting one another.

The heating section core 2 and the non-heating section core 3 are now secured to one another.

Figure 5 illustrates a mineral insulated heater cable 11 comprising a coupling 1 as described above. The cable 11 comprises the coupled cores 2, 3 surrounded by an insulator layer 12, which in this embodiment is formed from blocks of magnesium oxide. The cores 2, 3 and insulator layer 12 are encased in a stainless steel sheath 13 that is continuously formed from a flat stainless steel strip.

To assemble the cable 11, the heating section core 2 and the non- heating section core 3 are first formed.

The heating section core 2 and the non-heating section core 3 are then coupled together as described above. The heating section core 2 and the non-heating section core 3 are then surrounded radially by blocks of magnesium oxide, which forms the insulator layer 12.

The heating section core 2, the non-heating section core 3 and the insulator layer 12 are then encased in a stainless steel sheath 13. Figure 6 shows the resulting cable 11 being compacted by passing it through a set of rollers 14 of a roll reduction mill, which cold reduces the diameter of the cable 11 but increases its length. Thus, the roll reduction mill also reduces the diameter of the coupling 1 and increases its length. The cable 11 is passed through the roll reduction mill several times until its diameter and length reach the specified requirements. This process also provides compaction and a high pressure crimping force, which colds welds the join of the coupling 1 and thus increases the joint strength. This improves the electrical connection between the heating section core 2 and the non-heating section core 3.

The cable 11 is then passed through an induction annealing coil where it is heated to a predetermined temperature.

The cable 11 is then passed through a quenching system to relieve stress from the cable formation process and remove the effects of work hardening.

With this arrangement, since the heating section core 2 and non-heating section core 3 engage with one another, they are more securely connected together than with conventional arrangements in which the cores 2, 3 are only welded together. Thus the mechanical strength of the coupling 1 is increased relative to conventional couplings. In addition, the pre-engagement of the cores 2, 3 before cold reduction ensures that they are very tightly fastened together at the point of being permanently joined together by cold welding. This improves the electrical connection between the cores 2, 3, across the coupling 1, relative to conventional couplings.

The above embodiments are described by way of example only. Many variations are possible without departing from the scope of the invention as defined in the appended claims.