WO2021043759A1

WO2021043759A1 - An energy system for supply of power to a mobile offshore drilling unit

Info

Publication number: WO2021043759A1
Application number: PCT/EP2020/074332
Authority: WO
Inventors: Thomas BORSHOLM; Håkon KLEPSVIK; Per Lund
Original assignee: Odfjell Drilling As
Priority date: 2019-09-02
Filing date: 2020-09-01
Publication date: 2021-03-11
Also published as: GB2602407B; GB2602407A; GB202203432D0; NO345864B1; NO20191054A1

Abstract

The invention is related to an energy system for supply of power to a Mobile Offshore Drilling Unit. The energy system comprises: - a first storage and supply device, - a second storage and supply device, - a remote power generation source for supplying power to the first and/or second storage and supply device via one or more electrical cables. The first storage and supply device are configured to store and provide sufficient power for one or more end-users onboard the Mobile Offshore Drilling Unit during normal operations, and wherein the second storage and supply device as a minimum is configured to store and provide sufficient power to secure a well, as an emergency preparedness, in case of a combined situation of a well control incident and loss of the remote power generation source. The invention is also related to a Mobile Offshore Drilling Unit and a method thereof.

Description

AN ENERGY SYSTEM FOR SUPPLY OF POWER TO A MOBILE OFFSHORE

DRILLING UNIT

The present invention relates to energy system for supply of power to a Mobile Offshore Drilling Unit for well operations. The present invention is also related to a Mobile Offshore Drilling Unit (MODU) that is supplied with power from an external source, in combination with a system for onboard power storage and supply using electrochemical cells (batteries) and kinetic energy preservation device (flywheels), or a high-capacity capacitor (super capacitator or ultra-capacitator).

The present invention also relates to a method for supply of power to the Mobile Offshore Drilling Unit, where the Mobile Offshore Drilling Unit comprises an energy system.

In the field of oil well operations, a significant amount of power is required during the operation activity. The power requirements as used on, for instance a drilling rig serve to supply the draw works, the mud pumps, the top drives, the rotary tables and other peripheral loads. For Mobile Offshore Rigs (MODUs), station keeping systems in the form dynamic positioning systems and thrusters are often used to keep the rig in position over the well. In oil well operation activities, oversized power systems are often used so as to meet the peak power requirements.

During normal drilling operations, there is a base load of lighting, pumps, agitators, mixers, air compressors, etc. This base load may make up typical loads of 5 megawatts. The mud pumps, top drives and rotary tables contribute another fairly consistent kilowatt/megawatt demand. This demand will vary based on the particular well, depth of drilling, and material being drilled.

During oil well drilling activities, the most intermittent load is the draw works. This intermittent load is directed toward the peak demand during the raising of the drill pipe and casing upwardly in the well. This peak demand may have loads as much as 2 - 3 times the base loads of the other demands on the drilling rig. During the lowering of the drill pipe and casing downwardly in the well, the braking system needs to absorb energy in a similar order of magnitude.

The drilling process involves running and pulling of drill pipe on a routine basis (not only for inspection and changeout of drill bits). The drilling process involves drilling of a number well sections, each section comprising drilling to required depth, pulling out drill pipe, running of casing and cementing the casing. Thereafter the steps are repeated for each new section.

During the tripping pipe in or out of the well, the driller (operator) demands extreme power consumption and very quick bursts as the driller raises the string of drill pipe or casing. It is common that to generate sufficient power on the vessels today: a number of independently redundant diesel-powered generators (up to typically eight), which are run in a combination in order to secure sufficient power for the operations at any time, as well as to have sufficient redundancy power for emergency preparedness for example in the case of a combined generator shutdown and well control incident should occur. In such an event, the MODU is required to have sufficient emergency power to secure the well, make the rig safe and evacuate the personnel. The result of this way of generating power on the vessels is that the diesel generators always run at a low load which is not optimal with respect to the fuel consumption and emissions.

A disadvantage of having permanent power generation onboard the MODU is that you will have to design the whole unit for the risks involved in storing and burning the fuels. This is solved by designing the MODU for a number of scenarios including fire, explosions, toxic gases, and more, and the corresponding exposure to personnel onboard the MODU and the ability to maintain integrity of the well. The storage and combustion of fuels onboard the MODU is therefore a significant cost driver when designing and constructing a MODU.

Current versions of MODUs are normally powered by diesel generators, which emit greenhouse gases like CO2 and NOx. It is therefore an objective of the present invention to provide a MODU with an energy system that is environmental friendly by eliminating or at least reducing the emission of greenhouse gases.

Another objective of the present invention is to provide an optimized energy system for supplying sufficient power to the MODU during normal drilling operations and for emergency preparedness, where the energy system minimizes or alleviate one or more of the disadvantages of the prior art.

The present invention relates to an energy system for supply of power to a Mobile Offshore Drilling Unit. The energy system comprises:

- a first storage and supply device,

- a second storage and supply device, - a remote power source for supplying power to the first and/or second storage and supply device via one or more electrical cables.

The first storage and supply device is configured to store and provide sufficient power for one or more end-users onboard the Mobile Offshore Drilling Unit during normal operations, and wherein the second storage and supply device as a minimum is configured to store and provide sufficient power to secure a well as an emergency preparedness in case of a combined situation of a well control incident and loss of the remote power source.

The first storage and supply device and the second storage and supply device may together store sufficient power for the MODU to be able to perform drilling operations and to secure and make safe the well, the MODU and its personnel for all relevant operational scenarios.

The first storage and supply device may be at least one of a flywheel or a capacitor.

The flywheel is a mechanical device specifically designed to efficiently store rotational energy (kinetic energy). Flywheels resist changes in rotational speed by their moment of inertia. The amount of energy stored in a flywheel is proportional to the square of its rotational speed and its mass. The way to change a flywheel's stored energy without changing its mass is by increasing or decreasing its rotational speed. Since flywheels act as mechanical energy storage devices, they are the kinetic-energy-storage analogue to electrical capacitors, for example, which are a type of accumulator. Like other types of accumulators, flywheels smooth the ripple in power demand, providing surges of high power output as required, absorbing surges of high power input (system-generated power) as required, and in this way act as low-pass filters on the mechanical velocity (angular, or otherwise) of the system.

The flywheel may be charged from the draw work (regenerate) and the power supply may or may not be from the remote power source.

The first storage and supply device may be adapted to store and provide sufficient power to end-users onboard the MODU during normal operation. The end-users may be primary equipment for performing drilling operations and/or for operating the MODU such as thrusters, DP system, draw works, pipe, casing, lighting, pumps, agitators, mixers, air compressors, etc.

The first storage and supply device may be adapted store and supply sufficient power to perform primary operations onboard the MODU. The primary operations may be for example: operating thrusters, operating draw works (rising and lowering the drill pipe and casing), tripping pipe in and out of the well, performing oil well drilling activities and running base loads such as lighting, pumps, agitators, mixers, air compressors, etc. The second storage and supply device may comprise a battery, a plurality of batteries, battery banks or a combination thereof.

An important function for the battery bank may be to store and provide sufficient power to the MODU at all times, including in a situation with power loss from the cable, the battery bank needs to have enough power to keep the well, rig and its personnel safe. This may be the primary function of the battery bank and the main reason why a system comprising only a flywheel and an external power source will not be a viable solution, since any practical version of the flywheel/capacitator will not have enough stored energy to power the drilling system in the time it takes to secure a well. Industry standards and regulation for drilling operations have strict requirements for contingencies for dealing with well control situations and power losses, including redundancy of power supply.

As an emergency preparedness, the second storage and supply device as a minimum is configured to store and provide sufficient power to secure a well in case of a combined situation of a well control incident and loss of the remote power source.

The battery bank of the second storage and supply device may also store and supply sufficient power to enable startup of emergency power system onboard the MODU, e.g. emergency generators.

Another function of the battery bank may be to even out the power consumption onboard the MODU so that the cable from the external power source may feed a minimum, constant power to the MODU. In this way the cable, and the remote power source, can be dimensioned to a load which is as small as possible.

The first storage and supply device and the second storage and supply device may also be combined in one device. The one device may provide sufficient power for the MODU similar to that described for the battery banks and flywheel/capacitor. Thus, the one device may be a capacitor having a capacity suitable for supplying requisite power to one or more end-users onboard the MODU and provide sufficient power in the case of power loss from the electrical cable, and sufficient power to enable startup of emergency power system.

The MODU of the present invention may be equipped with one or more diesel generators in combination with the first storage and supply device and the second storage and supply device. However, with the energy system as described, the one or more diesel generators may not run during normal operations.

The battery bank may be designed for “medium term” power fluctuations and for sufficient “emergency power storage” in case of power loss from the power supply cable, while the flywheel/capacitor may be designed for “short term” power fluctuations. The “short term” is directed to the peak power demands from one or more end-users onboard the MODU.

In this way the MODU may be designed with an optimal combination of a first power and supply device and a second power and supply device. Thus, allowing a better space utilization onboard the MODU since the battery bank can be dimensioned just big enough to supply a load which is just sufficient to secure the well in case of a combined situation of a well control incident and loss of the external power source. Furthermore, the use of diesel generators may be eliminated or at least reduced to a minimum.

The better space utilization and optimal power utilization may allow for smaller size MODUs. Smaller sizes MODUs may be easier to move, to anchor and may not require costly and energy consuming thrusters for dynamic positioning (DP) of the MODU.

The remote power source is arranged for supplying power to the first and/or second storage and supply device via one or more electrical cables.

The remote power source may be a cable from onshore, from a nearby oil and gas field center, or from a mobile offshore power plant. The field center may be connected to shore via a shore cable. In mature areas like the North Sea, many of the future wells and well intervention operations will be performed close to existing field centers, and thus green power will be available within a relatively short distance to supply a Mobile Drilling Unit. In more remote offshore areas, a mobile offshore power plant can be moored near the MODU. In areas near shore, the MODU can receive power directly from onshore.

The field centers may also be equipped or supplied with power from green energy sources like windmills.

Green power is a subset of renewable energy and represents those renewable energy resources and technologies that provide the highest environmental benefit.

The onshore power plant, the field centers and the mobile offshore power plant may each comprise a green power generation plant. The green power generation plant may be any “green fuel” power generator process such as: ammonium, hydrogen, biofuels, methanol, and other fuels that does not emit climate gases like C02 and NOx. Green fuel, also known as biofuel, is a type of fuel distilled from plants and animal materials, believed to be more environmentally friendly than the widely-used fossil fuels.

In order to move towards an offshore drilling process with zero emission of greenhouse gases, alternative “green fuels” like hydrogen and ammonium and power generation techniques like fuels cells are viable alternatives. Many of these fuels and processes have a higher risk of fire, explosion and toxic gases compared to the convention diesel generator and may represent a hazard that is not acceptable to combine with a manned MODU working on a live well operation. Therefore, these “green fuels” systems may advantageously be placed on an unmanned mobile offshore power plant.

Thus, since the use of alternative fuel (“green fuel” such as ammonium and hydrogen) involves certain risk and danger to personnel, the mobile offshore power plant may be an unmanned floating vessel that can be towed to any desired location in safe distance to the MODU. Furthermore, the mobile offshore power plant may be designed as either a floating vessel or a jackup barge.

One or more MODUs may be connected to and supplied by power from one or more mobile offshore power plants.

The green power generation plant may comprise a remotely operated system for refueling of green fuels.

The mobile offshore power plant comprising the green power generation plant may also comprise one or more tanks for storing fuel in order to generate electricity, together with a system to lower and rise the tanks between the mobile offshore power plant and a seabed in order to keep the fuel in liquid form.

The one or more tanks may be preinstalled at the seafloor and connectable to the mobile offshore power plant.

Some of the «green fuels» come in gas phase at atmospheric pressure but are in liquid phase at a certain water depth. As an example, ammonium has a condensation point of 7 bars, equal to the ambient pressure of approximately 70 meters water depth. By placing the storage tank at the seabed, the benefits of storing the “green fuels” in liquid phase can be achieved.

Furthermore, the surplus heat from any of these “green fuel” processes may be transferred to the MODU through one or more pipes, tubes or hoses, whereby the heat may be used for different purposes onboard the MODU. The green power generation plant may also produce electricity from wind, waves, sun or the like and would therefor comprise the different components and/or elements for such an electricity production. A person skilled in the art will know how to arrange such a green power generation plant in order to generate electricity, whereby this is not described any further herein.

The green power generation plant may comprise a remotely operated system for pulling in the one or more electric cables arranged between the MODU and the power generation plant, for instance if the cable between the MODU and the power generation plant is preinstalled prior to the MODU and the power plant arriving on location.

The present invention also relates to a Mobile Offshore Drilling Unit (MODU) for drilling or well intervention. The MODU comprises an energy system as described above, for creating, storing and supply of power to the MODU.

The present invention is also related to a Mobile Offshore Drilling Unit (MODU) that is supplied with power from an external source, in combination with a system for onboard power storage and supply using electrochemical cells (batteries) and kinetic energy preservation device (flywheels), or a high-capacity capacitor (super capacitator or ultra-capacitator).

The MODU is adapted to perform drilling operations or well intervention. The MODU may comprise a derrick, a hoist system, a rotary system, a circulation system, and a power system.

Furthermore, the MODU may in one embodiment be “free floating”, meaning that it does not have its own propulsion system, whereby the MODU must be towed or hauled by another vessel between the sites or areas in which it is to be operate.

The advantage is the increase space onboard the MODU and the great cost savings of not using expensive propulsion systems. The MODU may further be made smaller and more compact in size.

However, it can be envisaged that the MODU, for some applications, may comprise its own propulsion system.

The MODU may be moored to a seabed on site through a plurality of mooring lines, or the MODU may also be provided with a dynamic positioning system in order to be positioned and kept in a specific position above the seabed. The present invention also relates to a method for supply of power to the MODU, where the method comprises the following steps:

-utilizing a remote power source to continuously supply power to at least any one of a first storage and supply device and a second storage and supply device,

-utilizing the first storage and supply device to store and provide sufficient power for one or more end-users onboard the Mobile Offshore Drilling Unit, and - utilizing the second storage and supply device, as a minimum, to store and provide sufficient power to secure a well in case of a combined situation of a well control incident and loss of the remote power source.

The first storage and supply device may be at least one of a flywheel or a capacitor. The second storage and supply device may a plurality of battery or battery bank. Further objects, structural embodiments and advantages of the present invention will be seen clearly from the following detailed description, the attached drawings and the claims below. The invention will now be described with reference to the attached figures, wherein:

Figure 1 shows in a schematic way an embodiment of an energy system according to the present invention comprising an offshore field center.

Figure 2 shows in a schematic way an embodiment of an energy system according to the present invention comprising a mobile offshore power plant.

Figure 3 shows in a schematic way an embodiment of an energy system according to the present invention comprising a mobile offshore power plant with a detachable fuel tank that can be lowered to the seabed.

Figure 4 shows in a schematic way an embodiment of an energy system according to the present invention comprising a mobile offshore power plant and a submerged fuel tank. Figure 1 shows in a schematic way a first embodiment of an energy system for supply of power to a Mobile Offshore Drilling Unit (MODU) 1, where the MODU 1 is used to perform different offshore operations, for instance drilling and well interventions. The MODU 1 comprises a derrick, a hoist system, a rotary system, a circulation system and a power system, and the energy system for supply of power is used to operate and run these systems.

A first storage and supply device 2 and a second storage and supply device 3 are arranged onboard the MODU 1. The first storage and supply device may comprise at least one flywheel and/or capacitor, while the second storage and supply device 3 may comprise a battery, a plurality of batteries or a plurality of battery banks.

The first and second storage and supply devices 2, 3 are connected to a remote power source 4 or power generation plant through one or more electrical cables 5, whereby power is transferred from the remote power source 4 or power generation plant and to the first and/or second storage and supply devices 2, 3.

The remote power source 4 or power generation plant may in this exemplary embodiment be an offshore field center 9 arranged on a submerged structure. The field center 9 may also be a moveable floating vessel anchored to the seafloor. The remote power source 4 or power generation plant in figure 1 is connected to an onshore power plant (not shown) through an electrical cable 5.

Figure 1 illustrates the MODU 1 drilling on a satellite field and a subsea template nearby an existing field center 9, where the MODU is connected with a cable to the field center 9. The field center 9 is in this case connected to shore via a shore cable 5. In mature areas like the North Sea, many of the future wells and well intervention operations will be performed close to existing field centers 9, and thus green power will be available within a relatively short distance to supply a movable drilling rig.

The field centers 9 may be equipped with shore power or power from green energy sources like windmills (not shown). The field centers 9 may also produce electricity from wind, waves, sun or the like and would therefor comprise the different components and/or elements for such an electricity production.

The first and second storage and supply devices 2, 3 arranged onboard the MODU 1 may also be provided with power directly from an onshore power plant (not shown). The electrical cables 5 may then extend from the onshore power plant and directly to the first and second storage and supply devices 2, 3 arranged onboard the MODU 1

The remote power source 4 or plant may continuously supply power to the first and second storage and supply devices 2, 3, with the exception of whether the connection between them for some reason is broken or must be broken.

Figure 2 shows in a schematic way a second embodiment of an energy system for supply of power to the MODU 1, where the MODU 1 is used to perform different offshore operations, for instance drilling or well interventions. The MODU 1 comprises a derrick, a hoist system, a rotary system, a circulation system and a power system, and the energy system for supply of power is used to operate and run these systems.

A first storage and supply device 2 and a second storage and supply device 3 are then arranged onboard the floating vessel 1. The first storage and supply device may comprise at least a flywheel and/or capacitor, while the second storage and supply device 3 may comprise a plurality of batteries or a plurality of battery banks.

In figure 2, the remote power source 4 is a mobile offshore power plant 8 comprising a green power generation plant, where the green power generation plant produces the power that is supplied to the first and second storage and supply devices 2, 3. The mobile offshore power plant 8 may refill fuel from a floating supply vessel 11 connectable by one or more hoses 13 between the vessel 11 and the mobile offshore power plant 8.

The mobile offshore power plant 8 may comprise a remotely operated system for pulling in the one or more electric cables 5 such that a MODU or a floating vessel may easily be connected to the mobile offshore power plant 8.

The green power generation plant onboard the mobile offshore power plant 8 may generate the power from “green fuels” such as: ammonium, hydrogen, biofuels, methanol, and other fuels that does not emit climate gases like C02 and NOx.

The mobile offshore power plant 8 may also produce electricity from wind, waves, sun or the like and would therefor comprise the different components and/or elements for such an electricity production.

Since the use of alternative fuel (“green fuel” such as ammonium and hydrogen) involves certain risk and danger to personnel, the mobile offshore power plant 8 may be an unmanned vessel or an unmanned jackup barge.

The mobile offshore power plant 8 may be moveable such that it may be transported to any desired location for supply of green power to one or more users.

Figure 3 shows the mobile offshore power plant 8 supplying power to the MODU 1 via electrical cables 5. The MODU 1 and the mobile offshore power plant 8 are both anchored to the seabed 7 by individual anchor lines 6. The mobile offshore power plant 8 has in this version a detachable fuel storage tank 12 that may be lowered to the seabed after the power plant 8 has been anchored in location. The tank 12 is arranged for storing “green fuels” and arranged on the seafloor for achieving the “green fuel” in a liquid phase. The mobile offshore power plant 8 may further comprise a system to lower and rise the tank 12. Figure 4 shows a mobile offshore power plant 8 for power generation from “green fuels”. The plant 8 is connected to a submerged tank 12 located on the seafloor, which can be installed on the seabed independently from the mobile offshore power plant. The “green fuel” is supplied from the tank 12 via one or more hoses 14 to the mobile offshore power plant 8.

The mobile offshore power plant 8 may refill fuel from floating supply vessels 11 connectable by one or more hoses 13 between the vessel 11 and the mobile offshore power plant 8. The vessel may also refill the tank 12 directly or via the mobile offshore power plant 8.

While the present invention has been illustrated by the description of the various exemplary embodiments thereof, and while the embodiments have been described in considerable detail, it is not intended to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and methods and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the scope or spirit of the general inventive concept.

Claims

1. An energy system (S) for supply of power to a Mobile Offshore Drilling Unit (MODU) (1), wherein the energy system (S) comprises

- a first storage and supply device (2),

- a second storage and supply device (3),

- a remote power source (4) for supplying power to the first (2) and/or second (3) storage and supply device via one or more electrical cables (5), where the first storage and supply device (2) is configured to store and provide sufficient power for one or more end-users onboard the Mobile Offshore Drilling Unit (1) during normal operations, and wherein the second storage and supply device (3) as a minimum is configured to store and provide sufficient power to secure a well as an emergency preparedness in case of a combined situation of a well control incident and loss of the remote power source (4).

2. Energy system (S) according to claim 1, wherein the first storage and supply device (2) is at least any one of a flywheel or a capacitor, and the second storage and supply device (3) comprises a battery, a plurality of batteries or battery banks.

3. Energy system (S) according to claim 1, wherein the first storage and supply device (2) and the second storage and supply device (3) is combined in one device.

4. Energy system (S) according to claim 1 or 2, wherein the remote power source (4) is an onshore power plant and/or an offshore field center 9.

5. Energy system (S) according to claim 1 or 2, wherein the remote power source (4) is a mobile offshore power plant (8) comprising a “green power” generation plant.

6. Energy system (S) according to claim 5, wherein the “green power” generation plant generates power from at least any one of: wind, waves, sun, “green fuels», or a combination thereof.

7. Energy system (S) according to claim 5 or 6, wherein the mobile offshore power plant (8) is an unmanned vessel.

8. Energy system (S) according to any one of the preceding claims 5-7, wherein a surplus heat from the “green power” generation plant of the mobile offshore power plant (8) is transferred to the MODU (1) through one or more pipes, tubes or hoses.

9. Energy system (S) according to any one of the preceding claims 5-8, wherein the mobile offshore power plant (8) comprises a remotely operated system for refueling of green fuels.

10. Energy system (S) according to any of the preceding claims 5-9, wherein the mobile offshore power plant (8) comprises a remotely operated system for pulling in one or more underwater electrical cables (5) from or near a seabed (7).

11. Energy system (S) according to any of the preceding claims 5-10, wherein the mobile offshore power plant (8) comprises a tank (12) arranged on the seafloor for storing “green fuels” in liquid phase.

12. Mobile Offshore Drilling Unit (1) for drilling or well intervention, wherein the MODU (1) comprises an energy system (S) for supply of power to the MODU according to any of the preceding claims 1-11.

13. The Mobile Offshore Drilling Unit (1) according to claim 11, wherein the MODU (1) comprises a plurality of mooring lines (6) for mooring the unit (1) to a seabed (7).

14. The Mobile Offshore Drilling Unit (1) according to claim 11 or 12, wherein the MODU (1) is free floating without propulsion means.

15. A method for supply of power to a Mobile Offshore Drilling Unit (1) comprising an energy system (S) according to claim 1-11, wherein the method comprises the steps of:

-utilizing a remote power source (4) to continuously supply power to at least any one of a first storage and supply device (2) and a second storage and supply device (3),

-utilizing the first storage and supply device (2) to store and provide sufficient power for one or more end-users onboard the Mobile Offshore Drilling Unit (1), and

- utilizing the second storage and supply device (3), as a minimum, to store and provide sufficient power to secure a well in case of a combined situation of a well control incident and loss of the remote power source (4).