NO20231072A1 - Subsea Communication Apparatus - Google Patents

Description

The invention relates to an apparatus for communication between a remote location and a subsea installation.

When developing subsea hydrocarbon reserves a hole is drilled from into the seabed to a hydrocarbon producing formation. During the drilling process successive layers of pipe called casing, is installed into the borehole to isolate the well from the surrounding formations and to protect against oil spills. The well is completed by installing production tubing.

When performing operations in a subsea well it is necessary to establish a column insulating the well from the environment. This is usually in form of a marine riser that runs from a surface vessel to the subsea well. Equipment for installation or for performing operations in the well, such as setting tubing are run on a drill string.

In prior art systems an umbilical having several lines is used to carry hydraulic fluid as well as electrical cables for communication. This is needed to power the functions in the installation tool. The umbilical is spun out from a reel and strapped around the outside of the drillpipe attached using clamps that is successively fastened to the drillpipe as it is lowered into the marine riser.

However, this is a time-consuming operation with a high risk for accidents. Another drawback with this system is that pumps for providing hydraulic pressure is located on the platform where they take up valuable space.

In our prior application NO 22020537, the applicant has developed a system where all devises for power and control of a well tool is located in the well and proximate the tubing hanger. This application describes a system where modules containing pumps and control valves as well as batteries for providing power are all located in or near the tool.

However, there is still the problem of providing reliable communication so that the subsea equipment can be controlled and monitored without having to strap a cable to the drill pipe.

There are a number of proposals to solve this problem, for example using acoustics waves through the drillpipe or through the fluid inside the marine riser. However, this fluid is usually a brine and may also be contaminated with particles, mud or the like and wireless signals do not penetrate well through the fluid inside the riser.

In US patent application No.2013 168081 there is described a system for two-way communication through a pressure riser. The control signal may involve an acoustic signal, an optical signal, and/or an electromagnetic signal such as electrical dipole coupling or magnetic dipole coupling.

When electromagnetic waves travel through a medium, whether it is radio waves, visible light or any other frequency, they are subject to attenuation, which will reduce the strength of any communication signal over the distance it travels. The extent to which this happens, depends on the frequency of the electromagnetic signals, and the properties of the medium through which the electromagnetic waves travel. The attenuation in sea water of electromagnetic waves with frequency 1 GHz can be more than 34 dB per 10 cm. This means that the signal power may drop by a factor of more than 2500 as it travels through 10 cm of sea water. The attenuation in riser fluids such as brine may be even higher than in sea water. Due to the high attenuation, radio communication subsea is very challenging and by many considered impossible. This invention solves the problem of attenuation by displacing the brine, to minimize the thickness of the brine layer through which the electromagnetic signals travel. Instead of traveling through brine, the signals travel through a body made of a material with low attenuation, which displaces the brine and dramatically reduces the attenuation.

The aim of the invention is to remedy these problems. This is achieved by providing a first radio antenna located in a port and a second radio antenna embedded in a ring located inside the well.

This solution enables a first antenna housed in a probe located in a port of the BOP to communicate with a second antenna embedded in a ring located inside the subsea well.

Preferably the ring is made of a di-electric material such as an elastomer or plastic.

Preferably the cylinder has an outer diameter that is a close fit inside the BOP. This minimizes the loss of signal that must pass through the gap.

The invention will now be described in more detail with reference to the accompanying drawings, where

Fig.1 is an isometric drawing of the invention, and

Fig.2 is a horizontal section through Fig.1

In Fig.1 there is shown a surface vessel 1. A cable or umbilical 2 extends from the vessel to a control unit 3 located near a subsea blowout preventer (BOP) 10. A cable 4 runs from the control unit to an antenna 21 located in a port 16 in the BOP. The control unit has means for transforming an electrical signal to a radio signal and to send or receive both radio signals and electrical signals.

The BOP 10 is located on top of a wellhead (not shown). The BOP has a central bore with an inner wall 11. Normally the bore is filled with a brine.

The antenna 21 is inserted into the port 16 and fixed pressure tight with a flange 22 bolted to the BOP.

In one embodiment the antenna has a cork screw or coil shape with a tip 23 terminating a small distance from the central bore. Preferably, the tip of the antenna is about 1 – 2 mm from the inner wall 11 of the BOP.

In another embodiment (not shown), the antenna is straight with a transverse ring at its end.

The antenna is preferably centred in the bore and encased in a di-electric material such as an elastomer or plastic.

A drillpipe 14 extends from the surface vessel and is connected to a tool (not shown) at its lower end. The tool may be a tubing hanger running tool (THRT). As shown the drill pipe runs through the BOP.

A ring 12 is clamped around the drillpipe such that when the THRT is landed in the well head the ring will be at the location of the port 16.

In one embodiment the ring is a massive ring made of an elastomer or plastic material

In an alternative embodiment the ring is an inflatable rubber ring filled with a gas such as nitrogen or a di-electric fluid.

in yet another embodiment it is a sleeve that may be relatively thin-walled. It may also extend only a portion around the inner wall 11, for example 180 degrees.

The ring should be a close fit inside the BOP central bore. Preferably the gap 18 between the outer surface of the ring 12 and the central bore 11 is less than 10 mm. Since the BOP central bore is filled with brine that is an obstacle to signals, it is preferable that this gap is as small as possible as the brine in the gap may degrade with the radio signals.

A coaxial cable 15 is connected to a control unit in the well tool and extends from the control unit to the ring 12. A section 17 of the cable 15 has its insulation and outer sleeve removed. This enables this section to function as a radio antenna.

As is well known to persons skilled in the art the length of the antenna corresponds to the radio frequency.

Similar to control unit 3 the control unit in the well tool includes means for transforming an electrical signal to a radio signal (and opposite) and to send or receive both radio signals and electrical signals. The well tool can thus receive instructions from the surface via radio signals and translate the signals to electrical signals for functions in the well tool and can convert electrical signals from a sensor in the well tool to radio signals and transmit these radio signals to the control unit 3.

The control unit receives signals from the vessel or from another remote location. In use a signal will be sent from a surface vessel or from land to the subsea control unit. In the control unit the signal will be converted to radio signals. These radio signals can then be relayed through the antennas and to the control unit operating the well tool.

The embodiment disclosed above is illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. While the invention thus described with reference to a subsea blowout preventer (BOP) it should be understood that the invention can find use in other subsea environments. These may be a Christmas tree or a subsea flowline. In the interest of clarity, not all features of an actual implementation are described in this specification. Specifically, the relation between antenna length and radio frequency is not described in detail, as this may change according to circumstances and may be subject to further developments. Likewise, the material in the ring will be chosen according to the frequency of the signals, as it is well known to a person skilled in the art that different materials are suited for different frequencies. Moreover, it will be appreciated that such a development effort might be complex and time consuming but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of the present disclosure.

Claims (8)

1. Apparatus for communication between a remote location (1) and a subsea installation, comprising a pressure vessel, for example a BOP (10) connected to a well head; where the pressure vessel has a port (16) extending through its wall, and a control unit (3) located outside the pressure vessel, characterized in that it comprises a first radio antenna (21) located in the port (16), said antenna (21) communicating with the control unit (3), and a second radio antenna (17) embedded in a ring (12) located inside the BOP, said antenna (17) communicating with a control unit located inside the BOP.

2. Apparatus according to claim 1, characterized in that the ring (12) is a solid ring filled with a di-electric material.

3. Apparatus according to claim 1, characterized in that the ring (12) is an inflatable ring filled with a gas.

4. Apparatus according to claim 1, characterized in that the ring (12) is a thin-walled sleeve filled with a di-electric material

5. Apparatus according to claim 1, characterized in that the control unit(s) are arranged to convert electrical signals to radio signals or vice versa.

6. Method for communication between a remote location and a subsea well tool, characterized in the following steps:

- Sending electrical signals from the remote location (1) to a control unit (3) located close to a subsea BOP (10),

- Converting the electrical signals to radio signals,

- Transmitting the radio signals through a BOP port (16) to an antenna (17) located inside the BOP, and

- Further transmitting the signals through a cable (15) to the well tool.

7. Method according to claim 6, characterized in the step of converting radio signals to electrical signals in a control unit in the well tool.

8. Method according to claim 6, characterized in transmitting radio signals from the control unit in the well tool to the control unit (3) outside the BOP.