CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. Provisional Application No. 62/518,319, filed June 12, 2017, which is incorporated herein by reference.

BACKGROUND [0002] The present disclosure relates generally to electrically heated subsea flowlines, and in particular, relates to electrically heated subsea flowlines heated with mineral insulated cables.

[0003] Due to cool water temperatures (about 40° F (4.4° C)) in deep water offshore hydrocarbon recovery operations, hydrocarbon fluids flowing through subsea pipelines become very viscous or deposit paraffin when the temperature of the fluid drops, adversely affecting fluid flow in the pipeline. Hydrocarbon gas under pressure combines with water at reduced temperatures to form a solid material, called a "hydrate." Hydrates can plug pipelines and the plugs may be very difficult to remove.

[0004] One solution involves electrical heating of the subsea pipeline to prevent excessive cooling of the fluid hydrocarbons. Heating by a variety of electrical methods has been known. Two configurations for electrical heating have been considered. One configuration, called a Single Heated Insulated Pipe (SHIP) system uses a single, electrically insulated flowline with current passing along the flowline. Another configuration is called a pipe-in-pipe system (EHPIP). Examples of SHIP and EHPIP systems are described in U.S. Patent Nos. 6,142,707, 6,171,025, 6, 179,523, 6,264,401, 6,292,627, 6,315,497, and 6,371,693, the entireties of which are hereby incorporated by reference. These solutions however may not be ideal as they may have a very high energy loss to the environment and may not be rated for continuous high power or high temperature operation. [0005] Another method of heating subsea flowlines is the use of short length, low voltage MI heater cables. MI heater cables are mineral insulated cables. Examples of mineral insulated cables are described in U.S. Patent Application Publication No. 2015/0285033, the entirety of which is hereby incorporated by reference. Low voltage MI heater cables, however, require an electric power bus and many connections and splices. They are not compatible with plugged subsea flowline remediation as they are not conducive to an independent, stand-alone, user adjusted heater source.

[0006] It is desirable to develop an improved electrically heated subsea flowline that does not suffer the disadvantages of conventional electrically heated subsea flowlines.

SUMMARY

[0007] The present disclosure relates generally to electrically heated subsea flowlines, and in particular, relates to electrically heated subsea flowlines heated with mineral insulated cables.

[0008] In one embodiment, the present application provides an electrically heated subsea flowline comprising: a flowline and a mineral insulated cable attached to the flowline.

[0009] In another embodiment, the present application provides, an electrically heated subsea flowline system comprising: a flowline, a mineral insulated cable attached to flowline, and a power source providing power to the mineral insulated cable.

BRIEF DESCRIPTION OF THE FIGURES

[0010] A more complete and thorough understanding of the present embodiments and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings.

[0011] FIG. 1 is an illustration of one embodiment of an electrically heated subsea flowline according to the present invention.

[0012] FIG. 2 is an illustration of one embodiment of a power cable according to the present invention.

[0013] FIG. 3 is an illustration of one embodiment of an electrically heated subsea flowline system according to the present invention. [0014] FIG. 4 is an illustration of one embodiment of a cross over in accordance with the present invention. [0015] The features and advantages of the present disclosure will be readily apparent to those skilled in the art. While numerous changes may be made by those skilled in the art, such changes are within the scope of the disclosure.

DETAILED DESCRIPTION

[0016] The description that follows includes exemplary apparatuses, methods, techniques, and/or instruction sequences that embody techniques of the inventive subject matter. However, it is understood that the described embodiments may be practiced without these specific details.

[0017] The present disclosure relates generally to electrically heated subsea flowlines. More specifically, the present disclosure relates to electrically heated subsea flowlines heated with mineral insulated cables.

[0018] Advantageously, the electrically heated subsea flowlines described herein allow for thawing cycles rather than continuous power for improved operating expenses, lower overall electrical power consumption, and improved efficiency. The mineral insulated cables of the present invention are more reliable for heating subsea flowlines in subsea applications as compared to conventional heating methods, thereby reducing the need for redundancy as required for polymer-type heating cables and reducing capital expenditures.

[0019] Embodiments of the mineral insulated cables discussed herein can be used, for example, without limitation, to maintain temperature in a subsea flowline, heat up materials in a subsea flowline through their respective phase change, or increase the temperature of a subsea flowline to allow solvents to melt or chemically change asphaltenes within a subsea flowline. Advantageously, the mineral insulated cables described herein can be used to pin point heating of a portion of a subsea flowline or designed heating of a subsea flowline.

[0020] Referring now to Figure 1, an electrically heated subsea flowline 100 has a flowline 110 and a cable 120.

[0021] The flowline 110 may comprise any conventional type of subsea flowline. For example, the flowline 110 may be a riser. Alternatively, the flowline 110 may be a subsea production pipeline. In another embodiment, the flowline 110 may comprise coiled tubing. [0022] The flowline 110 has an outer surface 111 and an inner surface (not illustrated in Figure 1). In one embodiment, the outer surface 111 is insulated and/or coated. In another embodiment, the outer surface 111 is not insulated and/or coated. The flowline 100 may be constructed of any conventional subsea flowline materials. The flowline 110 may be used to transport oil and gas, inject fluids into a subsea well or a subsea production pipeline, and combinations thereof.

[0023] The cable 120 is a mineral insulated cable. In one embodiment, the cable 120 is a three-phase electrical power cable.

[0024] Referring now to Figure 2, the mineral insulated cable 200 has one or more electrical conductors 238, preferably one, two, three, four, or five individual single electrical conductors 238. In the embodiment shown in Figure 2, the mineral insulated cable 200 has three single electrical conductors 238. The mineral insulated cable 200 preferably has a single phase, single cable design, a single phase, dual cable design, or a three phase, three cable design. The mineral insulated cable 200 may comprise a single electrical circuit or multiple electrical circuits. In a particular example, the mineral insulated cable 200 has a dual cable and three cable design, and is installed within a carrier tubing, such as a coiled tube.

[0025] Each of the individual single electrical conductors 238 illustrated in Figure 2 has conductive cores 228, mineral insulation 230, and a protective sheath 232. The conductive cores 228 are formed of an electrically conductive material, for example, without limitation, copper and/or aluminum. For example, a first portion of conductive cores 228 may be formed of a different conductive material than a second portion of conductive cores 228. As another example, the conductive cores 228 have multiple portions formed of different conductive materials.

[0026] The mineral insulation 230 is preferably a high temperature insulator material, including, without limitation, magnesium oxide (MgO) or a derivative thereof. Preferably, the mineral insulation 230 is constructed of inorganic material to avoid damaging carbonization in high temperature and/or high pressure environments. As shown in the embodiment illustrated in Figure 2, the mineral insulation 230 preferably surrounds the conductive cores 228, for example by direct contact with the conductive cores 228. [0027] As illustrated in Figure 2, the protective sheath 232 surrounds the mineral insulation 230, preferably in direct contact with the mineral insulation 230. The protective sheath 232 is formed of a material suited for protecting the conductive core 228 in the environment in which it is deployed. For example, the protective sheath 232 in the illustrated examples is constructed of a material that can provide physical protection to the conductive core 228 in a wellbore environment and in a high temperature environment. The protective sheath 232 may be constructed of a metallic material, such as, without limitation, stainless steel, duplex stainless steel, nickel iron, INCOLOY 825, INCOLOY 800, MONEL, carbon steel, lead or the like. In a preferred embodiment, the protective sheath 232 may be a seam welded metal jacket or may have similar construction. The protective sheath 232 is preferably constructed of inorganic material to avoid damaging carbonization in high temperature and/or high pressure environments.

[0028] In the embodiment illustrated in Figure 2, the protective sheath 232 is of unitary construction. Alternatively, the protective sheath 232 may be constructed of multiple sheaths, e.g., an inner sheath and an outer sheath. The inner sheath and the outer sheath may be formed of the same or of different materials. When multiple sheaths are used, each sheath may be constructed of an inorganic material to avoid damaging carbonization in high temperature and/or high pressure environments.

[0029] As depicted in Figure 2, the mineral insulated cable 200 has an outer jacket 234. The outer jacket 234 may be constructed of a metallic material such as without limitation, stainless steel, duplex stainless steel, nickel iron, INCOLOY 825, INCOLOY 800, MONEL, carbon steel, lead or the like. Preferably, the outer jacket 234 is constructed out of a material that is corrosion resistant and temperature compatible. As illustrated in Figure 2, the outer jacket 234 surrounds each of the electrical conductors 238, for example, as shown by wrapping several electrical conductors 238 with the outer jacket 234. Alternatively, each of the single electrical conductors 238 may be joined by spiraling the individual single electrical conductors 238 in a helical fashion and/or wrapping with the outer jacket 234. The outer jacket 234 advantageously provides additional corrosion resistance while the protective sheath 232 provides additional axial strength or vice versa.

[0030] In the embodiment illustrated in Figure 2, each of the individual single electrical conductors 238 are shown positioned and joined to form a power cable 200 that has a planar shape. In other embodiments, not illustrated in Figure 2, each of the individual single electrical conductors 238 may be positioned relative to each other in a non-planar shape, for example triangular or cylindrically shaped power cable 200.

[0031] The mineral insulated cable 200 may be a high voltage, medium voltage, or low voltage cable. [0032] Referring back to Figure 1, the cable 120 preferably has features discussed above with respect to the mineral insulated cable 200 shown in Figure 2.

[0033] In the embodiment illustrated in Figure 1, the electrically heated subsea flowline 100 has a clamp 130. The clamp 130 may be constructed out of any material sufficient for use in clamping the cable 120 to the flowline 110. It will be understood by those skilled in the art, however, the clamp 130 is not necessary in all embodiments, for example when the cable 120 is disposed within the flowline 110.

[0034] In accordance with the present invention, the electrically heated subsea flowline 100 can be buried in a seafloor. Preferably, the electrically heated subsea flowline 100 has one or more coatings, for example, without limitation, a passive insulation coating and/or a protective covering. In such embodiments, the cable 120 may be installed next to the flowline 110 and a passive insulation coating and/or a protective covering may be provided for both the cable 120 and the flowline 110.

[0035] The passive insulation coating may be any conventional insulation coating material. The protective covering may be any conventional covering material. [0036] In the embodiment illustrated in Figure 2, the electrically heated subsea flowline 100 has an end termination assembly 160. The end termination assembly 160 provides a fitting for receiving multiple electrical conductors 238 spliced together. For example, three electrical conductors 238 may be spliced together into the end termination assembly 160 to electrically couple the electrical conductors 238 in a three-phase wye configuration. As another example, two electrical conductors 238 may be spliced together into the end termination assembly 160 to electrically couple the electrical conductors 238 in a split-phase center tap configuration. [0037] The end termination assembly 160 may be completely welded together, insulated or not insulated from an electrical grounding reference. The end termination assembly 160 may be arranged in such a manner that it will lay on the outer surface 111 of the flowline 110 with a similar curvature as to be like the flowline 110 outer surface 111. The end termination assembly 160 may comprise any combination of features of the end terminations described in US Patent No. 8,586,867, the entirety of which is hereby incorporated by reference.

[0038] In a preferred embodiment, for example when the flowline 110 is a riser, the flowline 110 may be heated internally from a platform to a mudline using the cable 120.

[0039] Referring now to Figure 3, an electrically heated subsea flowline system 1000 has an electrically heated subsea flowline 1100.

[0040] The electrically heated subsea flowline 1100 may comprise any combination of features discussed above with respect to the flowline 110 and/or the electrically heated subsea flowline 100. In the embodiment depicted in Figure 3, the electrically heated subsea flowline 1100 has a flowline 1110, a mineral insulated cable 1120, clamps 1130 and an end termination assembly 1140.

[0041] The flowline 1110 may comprise any combination of features discussed above with respect to flowline 110. The mineral insulated cable 1120 may comprise any combination of features discussed above with respect to the cable 120 and/or the mineral insulated cable 200. In certain embodiments, the clamps 1130 may comprise any combination of features discussed above with respect to the clamp 130.

[0042] As shown in the embodiment of Figure 3, the cable 1120 is clamped onto an outer surface of the flowline 1110 by one or more clamps 1130. The mineral insulated cable 1120 may be attached to the flowline 1110, for example, at the 6 o'clock position, or, as shown in Figure 3, the mineral insulated cable 1120 may be attached to the flowline 1110 at the 12 o'clock position. In another embodiment, the mineral insulated cable 1120 may be disposed within the flowline 1110.

[0043] The flowline 1110 may be provided with a coating (not shown). In the embodiment shown in Figure 3, the electrically heated subsea flowline 1100 is shown on the seafloor. However, in accordance with the present invention, all or a portion of the electrically heated subsea flowline 1100 may be buried beneath the seafloor.

[0044] In the embodiment illustrated in Figure 3, a power source 1200 supplies power to the electrically heated subsea flowline 1100. As illustrated, the power source 1200 is located on a floating vessel 1300. Alternatively, the power source 1200 may be located on a fixed facility. Preferably the power source 1200 has a variable voltage transformer, for example, having up to 32 taps for power supply rangeability and variable control. Preferably, the power source 1200 has an embodiment of a variable voltage transformer described in US Patent No. 7,866,386, the entirety of which is hereby incorporated by reference. [0045] When the flowline 1110 is a riser or coiled tubing, the mineral insulated cable 1120 is advantageously connected directly to the power source 1200.

[0046] In the embodiment illustrated in Figure 3, an umbilical cable 1400 is used to connect the mineral insulated cable 1120 to the power source 1200.

[0047] The umbilical cable 1400 may be any type of conventional umbilical cable. For example, the umbilical cable 1400 may be a multi-conductor power cable that can utilized to transmit the electrical power from the power source 1200 to the mineral insulated cable 1120. The umbilical cable 1400 may comprise one or more single or three phase power circuits. Preferably, the umbilical cable 1400 is a dynamic type cable that can withstand constant movement in the subsea due the wave and current forces acting on the surface. [0048] In the embodiment of Figure 3, the umbilical cable 1400 is connected to the mineral insulated cable 1120 using a cross over system 1500.

[0049] Referring now to Figure 4, a cross over system 1500 has an umbilical cable 1400, a wet-mate plug 1501, a flex lead 1502, and an umbilical crossover 1503. The cross over system is preferably used for connecting the mineral insulated cable 1120 to the power source, for example, power source 1200 in the embodiment shown in Figure 3.

[0050] The wet- mate plug 1501 is any electrical connector that can be connected and disconnected under water for connecting the umbilical cable 1400 to the flexible lead 1502. [0051] The flexible lead 1502 is a flexible cable for connecting the wet-mate plug 1501 to the mineral insulated cable 1120.

[0052] The umbilical cross over 1503 is used to connect the flexible lead 1502 to the mineral insulated cable 1120. The umbilical cross over 1503 may be a 3-way umbilical cross over. Preferably, the umbilical cross over 1503 is an oil filled device. More preferably, the umbilical cross over 1503 may comprise an MI (mineral insulated) connector for connecting the mineral insulated cable 1120 to the flexible lead 1502.

[0053] In the embodiment shown in Figure 4, the flexible lead 1502 is connected to a cold lead portion 1121 of the mineral insulated cable 1120. The cold lead portion 1121 of the mineral insulated cable 1120 may have a different conductive core than the remaining portion of mineral insulated cable 1120. For example, the cold lead portion 1121 can have a conductive core consisting of pure copper, alloy 30 copper, or alloy 60 copper. The cold lead portion 1121 of the mineral insulated cable 1120 is of a length required for a predetermined cross over system. Preferably, the cold lead portion 1121 has a length in a range from 5 to 100 feet (1.5 to 30 m) long, more preferably from 10 to 100 feet (3 to 30 m) long, and even more preferably from 50 to 100 feet (15 to 30 m) long. Preferably, the cold lead portion 1121 of the mineral insulated cable 1120 has a conductive core that generates less heat than the conductive core in the remaining portion of the mineral insulated cable 1120.

[0054] An advantage of the present invention is that the electrically heated subsea flowlines and the electrically heated subsea flowline systems are capable of providing pin point heating of a subsea flowline. For example, the mineral insulated cable 1120 may be configured to heat only a specific portion of the subsea flowline 1110, preferably a portion of the subsea flowline having a length in the range of from 1 mile to 20 miles (1.6 to 32 km). [0055] Another advantage of the present invention is that the electrically heated subsea flowlines and the electrically heated subsea flowline systems can be used to provide designed heating of a subsea flowline. For example, the mineral insulated cable 1120 of the present invention can be implemented to heat different portions of the flowline 1110 at different rates simultaneously. As another example, the mineral insulated cable 1120 can be implemented with a first portion that heats a first portion of a subsea flowline at a heating rate in the range of from 0% to 5% to the maximum heating rate of the mineral insulated cable 1120 and a second portion of the mineral insulated cable 1120 for heating a second portion of subsea flowline at a heating rate in the range of from 5% to 60% of the maximum heating rate of the mineral insulated cable 1120. As a further example, the mineral insulated cable 1120 can be implemented with a third portion for heating a third portion of the subsea flowline 1110 at a heating rate in the range of from 60 to 100% of the maximum heating rate of the mineral insulated cable 1120. The implementation can be effected by, for example, the first, second, and third portions of the mineral insulated cable 1120 having a different conductive core material, for example, different alloys. Each of the first, second, and third portions of the subsea flowline 1110 may have a length in the range of from 1 to 20 miles (1.6 to 32 km), more preferably in the range of from 5 to 10 miles (8 to 16 km).

[0056] Advantageously, the electrically heated subsea flow line 1100 of the present invention can be used to inject a heated fluid, such as a solvent or an inhibitor, into a second subsea flowline, one or both of which may be a coiled tubing. [0057] Still another advantage of the present invention is that the electrically heated subsea flowlines and the electrically heated subsea flowline systems may be utilized to upgrade crude oil while it is being transported in the flowline. In one embodiment, the MI cables of the present invention are configured to heat portions of the flowline to conversion temperatures. In another embodiment, the flowlines are pigged, for example with deposits directed to a subsea disposal tank to capture precipitated coke, resulting from the upgrading.

[0058] Use of the flowlines to partially or fully upgrade hydrocarbons during transportation could be especially useful in locations of aging or lacking refinery capacity or in developments of crude that require upgraded products to create a more commercially suitable hydrocarbon mix. The containment space of the flowline may serve a dual purpose of providing the means of transportation of the hydrocarbons and water and that of a hydrocarbon upgrader. The portion of the flowline used for the upgrading may comprise corrosion resistance materials. The length of the section set up for reaction must have enough residence time (hours) to allow a significant level of hydrocarbon conversion. In this application of the present invention, the flowline may be regularly wiped inside with rubber darts pumped from a pigging launching section at the start of the flowline upgrader section. During the pigging process, the flowline may be redirected to a coke subsea disposal tank where the wiper can push the precipitated coke product into the tank. Hydrogen may be injected into the portion of the flowline used for the upgrading. This can be accomplished by placing by the flowline hydrogen production from the water in the seabed and injecting that hydrogen to the flowline to be heated.

[0059] As discussed above, the MI cable may be provided inside the flowline. In this case, the insertion of MI cables inside the flowlines would be enabled by configurations and processes used for subsea well interventions. For example, the flowline can be provided with an entry point to allow installation and maintenance of the MI cable. This entry can be vertical, horizontally deviated or horizontal depending on the subsea intervention equipment that available in the region. For example, the MI cable may be inserted in a similar construct and functionality as for a well completion hanger and head with wet mate connections above the hanger and/or head for the cold elements of the heater to feed through the entry point. Similar well functionality for intervention and containment control may be needed to prevent any leaks to the seafloor coming from the flowline. This may come in the form of a swab valve on top of the heater hanger to isolate the flowline from a lubricated rig up to introduce the heater cables.

[0060] In another embodiment of an electrically heated subsea flowline system, a mineral insulated cable installed inside the flowline has a power termination attached to electrically heated subsea flowline system. Such a system may require pressure rated fittings. Additionally, it may be advantageous to provide the power supply for the system inside the flowline.

[0061] From the foregoing detailed description of specific embodiments, it should be apparent that a system for a high temperature power cable that is novel has been disclosed. Although specific embodiments have been disclosed herein in some detail, this has been done solely for the purposes of describing various features and aspects and is not intended to be limiting with respect to the scope of the claims herein. It is contemplated that various substitutions, alterations, and/or modifications, including but not limited to those implementation variations which may have been suggested herein, may be made to the disclosed embodiments without departing from the scope of the appended claims which follow.