EP4202179A1

EP4202179A1 - A method of detecting and locating a co2 leak from a seabed

Info

Publication number: EP4202179A1
Application number: EP22215779.4A
Authority: EP
Inventors: Jason MOORSE; Benjamin CANNELL
Original assignee: Aquaterra Energy Ltd
Current assignee: Aquaterra Energy Ltd
Priority date: 2021-12-23
Filing date: 2022-12-22
Publication date: 2023-06-28
Also published as: GB202118968D0

Abstract

A method of detecting a CO2 leak from a seabed comprises the steps of:• Submerging a monitoring structure which houses a sensor array which comprises a sonar sensor, a tidal direction and velocity sensor and a dissolved-gas sensor.• Transmitting a sonar signal from said sonar sensor, which is suitable for detecting a CO2 gas bubble rising from a sea bed;• Transmitting a second signal from said tidal direction and velocity sensor, which is suitable for detecting the direction and velocity of a tide flow;• Testing the tidal water about said dissolved-gas sensor, which suitable to detect dissolved CO2 molecules;• Generating data which comprises data generated by said sonar sensor, said tidal direction and velocity sensor, and dissolved-gas sensor.• Transmitting said CO2 data for said monitoring structure to a processing means to determine a CO2 leak and its location on the seabed.

Description

Field of the Invention

The present invention relates to a method for detecting and locating CO2 (CO2 being in a gaseous or dissolved state) leaking from a seabed by the means of "a sensor array" located within a submerged housing.

Background to the invention

The present invention seeks to address the problem of detecting and locating a CO2 leak from a seabed, primarily in the offshore oil industry, and in particular the offshore Carbon capture and storage (CCS) methods suitable for CO2 storage.
CCS is a well-known emissions' reduction technology that has been utilised for many years by oil and gas operators. Worldwide the number of CCS projects being initiated is increasing everyday as industry and governments' demands drive forward the requirement for energy transition from fossil-based energy production to renewable energy sources.
CCS can be used to store CO2 away from the atmosphere in subsurface formations (e.g. legacy oil and gas formations and saline aquifers), safely and on a geological time frame. Recent wildfires that have ravaged countries across the globe illustrate the risks of relying on purely nature-based solutions to do the same (e.g. tree planting).
Thus, CCS can be utilised for implementing a successful blue hydrogen supply chain and is suitable for other carbon-generating industries. In this new context, mature offshore oilfields are newly useful, and depleted offshore reservoirs become valuable storage assets.
However, there is a number of critical engineering considerations and competencies required in successfully repurposing legacy offshore formations as carbon storage. CO2 leak detection and response planning are essential elements in the development and long-term storage of any project, reducing environmental risk and providing reassurance of asset integrity.
Thus, the ability to guarantee the detection and location of any CO2 leakage and provide a means to fix the issue is critical to the success of offshore CO2 storage.
It is an object of the present invention to provide method for detecting and locating a CO2 from a seabed to address the above problems.

Summary of the Invention

In first broad independent aspect the invention provides a method of detecting a CO2 leak from a seabed comprising the steps of:

Submerging a monitoring structure which houses a sensor array which further comprises a sonar sensor, a tidal direction and velocity sensor and a dissolved-gas sensor;
Transmitting a sonar signal from said sonar sensor, which is suitable for detecting a CO2 gaseous bubble rising from a seabed;
Transmitting a second signal from said tidal direction and velocity sensor, which is suitable for detecting the direction and velocity of a tide flow;
Testing the tidal water about said dissolved-gas sensor, which sensor is suitable to detect dissolved CO2 molecules;
Generating CO2 data which comprises data generated by said sonar sensor, said tidal direction and velocity sensor, and dissolved-gas sensor.
Transmitting said CO2 data for said monitoring structure to a processing means to determine a CO2 leak and its location on the seabed.

The method provides the advantage of detecting the presence of a CO2 leak from a seabed. The sonar sensor can detect a CO2 leak in a gaseous bubble state within a 500-meter radius of the monitoring structure. The tidal flow and tidal velocity sensor can detect the detected direction and velocity across a water column about the monitoring structure. The dissolved-gas sensor can detect the level of dissolved CO2 molecules being carried by the monitored water column about the monitoring structure.
Thus, the data generated for indicating direction and velocity of the detected CO2 molecules or bubbles can be subsequently processed to determine the location of a CO2 leak from a seabed.
Preferably the method comprises the further step of:

Detecting a submarine sound indicative of a gas bubble rising from a seabed with a hydrophone device comprised within said sensor array.

The hydrophone device detects the presence and direction of gaseous bubbles raising from the seabed.
Preferably the method comprises the step of:

generating data indicative is indicative of a CO2 level detected by said dissolved-gas sensor and a tidal direction and velocity detected by said direction and velocity sensor.

The data obtained from both the dissolved-gas sensor and tidal direction and velocity sensor is subsequently processed to determine the location of a CO2 leak is determined by the detected direction and velocity of the tidal flow comprising the detected CO2 molecules relative to the monitoring structure.
Preferably the method comprises the step of:

Generating data indicative of a gas bubble detected by said sonar sensor and an audible vibration detected by said hydrophone device.

The data obtained from both the sonar sensor and the hydrophone device is subsequently processed to determine the presence of gas bubbles and the detected audio vibrations confirm the location of these gaseous bubbles relative to the monitoring structure.
Preferably the method comprises the step of

Tethering a buoy device to said monitoring structure via an umbilical attachment means.

The buoy provides a navigational marker for sea traffic. The buoy has a beacon device so that it can observed in low light/night conditions. The umbilical attachment means is preferably a flexible elongate multicore electrical cable and/or optical fibre device. Preferably the method comprises the step of

Communicating electrical power and data communications between said buoy device and:
- ∘ said sonar sensor;
- ∘ said tidal direction and velocity sensor;
- ∘ said dissolved-gas sensor; and
- ∘ said hydrophone device;

The umbilical means enables the communication of electrical power from a power cell incorporated with the buoy, to the submerged monitoring structure. The power cell is typically one or more rechargeable battery cells which are connected to a solar panel array located about the exposed body of the buoy. The umbilical means also enables data communication from the sensors housed within the submerged monitoring structure, to the buoy. The data communication may also be duplex data communications which provides two-way data communication between the submerged monitoring structure, and the buoy.
Preferably the method comprises the step of

communicating said data indicative of CO2 location on seabed from said buoy, to a satellite communication device via a wireless satellite communication means.

The satellite communication enables the communication of CO2 data from the submerged monitoring structure to a computer device for subsequent processing via data network; when the buoy is located beyond the transmission range of other land-based wireless communication systems.
Preferably the method comprises a plurality of said monitoring structures arranged in a CO2 detection array on a seabed.
An array of monitoring structures located at predetermined locations on seabed enables the monitoring and detection of CO2 over a greater area. The detector signals of neighbouring monitoring structures, overlap each other, to provide a larger area of the seabed which can be monitored and observed for the detection of CO2 leaks.
Preferably the method comprises the step of

generating an alarm on a user interface which is indicative of detected CO2 exceeding a predetermined level.

The data indicative of the detected CO2 is processed to alert a user of the presence of a CO2 leak, along with its location. The user is provided with the sensed metrics for the CO2 which enables the user to make an informed choice on whether not a subsequent verification action is required. This action may be in the form of deploying a surface vessel comprising further additional sensors instrumentation to the site of the leak for further testing and analysis.
The user interface may be embodied in a Graphical user interface [GUI] computer software application, which communicates with other computer networks and applications, such as systems which alert and manage any follow up surface vessel requirements and/or subsequent testing.
This method of gas detection can be implemented for other forms of gas detection such as methane or other natural gases. Thus, the sensor array will require sensor adjustments accordingly, such as the dissolved-gas sensor etc.
In a second broad independent aspect the invention provides a CO2 monitoring structure suitable in accordance with any of the preceding claims for detecting a CO2 leak from a seabed, comprising a sensor array housed within said structure; wherein said array further comprises a sonar sensor, a tidal direction and velocity sensor and a dissolved-gas sensor.
In use, this monitoring structure configuration detects gaseous bubbles from a leak in the seabed, and subsequently determines if CO2 is being discharged from the leak.
Preferably the structure further comprising a hydrophone device.
The hydrophone senses audio vibrations of a gaseous bubbles rising from the seabed.
Preferably the structure further comprises an attachment means suitable for providing an operable connection to a tether device.
The tether enables a buoy device to be attached in relatively close proximity to a submerged monitoring structure and thus provide a navigational marker to sea traffic.
Preferably a tether in accordance with any of the above features comprising a multicore elongate body further comprising an electrical cable and/or an optical fibre.
The tether provides a means of communicating power and data communication between the submerged monitoring structure and the attached buoy.
Preferably a buoy device in accordance with any of the above features for detecting a CO2 leak from a seabed further comprising:

an attachment means for providing an operable connection to tether device,
A rechargeable battery cell operably connected to an external solar panel array,
A satellite communication means operably connected to said sensors of said monitoring structure, which in use communicates with a satellite telemetry system.

The buoy enables the communication of data from the submerged monitoring structure to a subsequent data network, via a satellite communication device.
Preferably a user interface in accordance with any of the above features for detecting a CO2 leak from a seabed further comprising:

Means of processing data indicative of detected CO2 and determining the CO2 source relative to said monitoring structure;
An alarm means which activates when the detected CO2 exceeds a predetermined level.

The user interface provides the means of alerting a user to the detection of CO2, its location relative to the submerged monitoring structure and that the detected CO2 is beyond a predetermined threshold.
In a third independent aspect the invention provides a system for detecting a CO2 leak from a seabed comprising:

A monitoring structure housing a sensor array which further comprises:
- ∘ a sonar sensor;
- ∘ a tidal direction and velocity sensor; and
- ∘ a dissolved-gas sensor
A communication means for communicating sensor data to a buoy;
A tether device for tethering said buoy to said monitoring structure, which further comprises an electrical cable and/or an optical fiber for communicating power and data between said buoy and said monitoring structure;
A satellite communication means for communicating sensor data to a satellite communication device.
A user interface in operable communication said satellite device, which further comprises a CO2 alarm means which in use determines that the detected CO2 has exceeded a predetermined level.

The system provides a user with a means monitoring an area of the seabed with one or more monitoring structures to detect the presence of a CO2 leak, along with its location on the sea floor relative to a monitoring structure. The user can then make an informed decision on how to respond to the detected CO2 leak.

Brief Description of the Figures

Figure 1 shows a diagram for a complete CO2 Monitoring, Measurement, Verification and Response [MMV-R] system.
Figure 2 shows a system diagram for a CO2 MMV - R sensor array of the invention.
Figure 3 shows perspective view of CO2 sensor node for the CO2 MMV - R system
Figures 4a to 4b show system diagrams of a data buoy attached to CO2 sensor node.
Figure 4c shows a data buoy in communication with a Satellite system.
Figure 5 shows the constituent components of a submarine data array
Figure 6a shows three variations of tidal movement.
Figure 6b shows tidal movement relative to a CO2 sensor node.
Figure 7 shows a sensor node sensing a CO2 leak from a seabed.
Figure 8 shows the graphical user interface [GUI] for the received processed data.

Detailed Description

Figure 1 shows a Monitoring, Measurement, Verification and Response [MMV-R] system generally indicated by arrow 1. The system 1 comprises an array of submarine sensor nodes 2, each sensor node 2 being tethered from a dedicated floating buoy device 3, via an umbilical cord 4.
Each submarine sensor node 2 has a sensing signal array 16, which is suitable for detecting a Carbon Dioxide CO2 leak 10 from a seabed 9. The CO2 leak 10 originates from a crack / fissure 11 within the seabed 9, which subsequently allows CO2 to escape a CO2 deposit 13 located beneath the seabed 9, into the sea 12.
Each buoy device 3 has a first wireless communication means 6, which is suitable for establishing data communication from the buoy, to an overhead satellite device 5. The satellite device 5 has a second wireless communication means 7, which is suitable for establishing data communication from the satellite device, to a computer device 8 via a computer network.
A response boat 14 verifies a leak by towing an array of additional submerged sensors 15.
Therefore, in use, the sensing signal array 16, detects and locates a CO2 leak 10 from a seabed 9. The data indicative of the CO2 leak 10 is then communicated from the submarine sensor node, to the tethered buoy device 3 via an interconnecting umbilical cord 4. The data indicative of the CO2 leak is then wirelessly communicated 6 to an overhead satellite device 5. The CO2 data is then subsequently wirelessly communicated 7 to a computer device 8 [either a portable or static computer device] via computer network [either a mobile [GSM - global system for mobile communications], Wide Area Network WAN or the like]. The computer device 8 then subsequently processes the data indicative of the CO2 to characterize the leak and its associated location[s].
Figure 2 shows an array of sensor nodes 2 located on a sea floor 20. Also located within the field of the array is an abandoned well 22 and a new injection well 23. Each sensor node 2 emits a signal 24 which is suitable for determining a CO2 leak. Located between two neighbouring sensor nodes 2 is a fault 25 within the seafloor 20. Each sensor node 2 is tethered to a dedicated buoy 3, via an umbilical cord 4.
In use, the array of sensor nodes 2 covers a CO2 injection site with overlapping sensors, which focus on areas of interest and accounts for ebb and flood tide movements. These tidal movement are essential for sensors to detect dissolved CO2.
Figure 3 shows a perspective view of a sensor node and is generally indicated by arrow 2. The sensor node 2 comprises a pyramidal cage structure 35, which houses an array of submarine sensors. The bottom supporting legs of the structure extend outwards to increase stability of the structure when mounted on an uneven surface. The cage narrows to a top central attachment plate, which balances and stabilizes the structure when being lowered and raised from the sea floor as well as providing an access slot for the sonar sensor. The sensor node 2 is tethered to a dedicated buoy device 3 via an umbilical cord 4.
The housed sensor array comprises the following sensors:

A CO2 detection sensor 31 such as the HydroC [TM] & CH4 Sensor [TM] types (dissolved-gas sensors);
A tidal current, pressure and temperature sensor 32 such as the Aquadopp sensor [TM];
A bubble monitoring Sonar head 33 such as the Sonardyne Sentry sensor [TM];
A hydrophone 34;

In use, tide water passes through both the open and meshed portions of the cage structure so that tide water passes over all the housed sensors.
Figure 4a shows a modular polymer data buoy platform 3 hardwired to a submerged sensor node 2 via an umbilical cord 4. The umbilical cord 4 is a stretch mooring umbilical device which is extendable to 2.5 times its initial length.
In use, the cord provides power to the submerged sensor; as well as providing a means of duplex data transmission between the buoy and the submerged node. The umbilical cord 4 also eliminates the risk of entanglement and reduces watch circles.
Figure 4b shows the umbilical cord 4 attached to both the data buoy platform 3 and submerged sensor node 2, bending in accordance with a movement of a sea tide.
Figure 4c shows the modular data buoy 3 with a means of providing a wireless satellite telemetry communication means 40, a navigation beacon device 41. A rectangular solar panel array 42 is mounted about the buoy 3 and is electrically coupled to an internal battery device [not shown]. A buoyancy means 43 is positioned at the water line of the buoy 3. A bend restricting device is located over the top portion umbilical cord 4 where it is attached the buoy 3.
In use, data and power is communicated from the buoy 3, to the submerged sensor node [not shown], via the umbilical cord 4. The power is provided by the enclosed battery, which is subsequently charged via the solar panel array 42 located about the body of the buoy 3. Thus, the solar array 42 can receive continuous solar radiation from the sun throughout the day, without being compromised by the actual positioning of the sun. The data received from the submerged sensor node, is then subsequently wirelessly transmitted to an overhead satellite communication device 45.
Figure 5 shows a sensor array which is housed within the sensor node 2 cage structure. The array is configured into two functional sub-arrays. The first sub-array 50 comprises a dissolved-gas sensor 31 and a tide current pressure, and temperature senor 32. The second sub array comprises a sonar sensor 33 and a hydrophone device 34.
In use, the dissolved-gas sensor 31 can detect traces of dissolved CO2 gas which enters its detection chamber via the movement of tidal water. The current direction and velocity can then be determined by the tide data collected by the tide sensor 32.
The combined data from the CO2 sensor 31 and the tide sensor 32 can be subsequently processed to:

pinpoint the location of the CO2 leak;
determine the leak detection being dependent upon the current direction;
detect the presence of CO2, and:
detect dissolved CO2.

The combined data from the sonar sensor 33 and the hydrophone 34 can be subsequently processed to:

detect traces of gas bubbles within a 500-meter radius and pinpoint the leak location;
The bubble detection is not dependent upon current direction;
The sonar cannot determine CO2 or any other gases;
Cannot detect dissolved CO2, and
The Hydrophone can confirm sonar detections.

Thus in use, the data generated by the synergistic combination of all the sensors within the whole data array can detect:

Gas bubbles;
Dissolved gas;
Gas/dissolved gas type [such as CO2]
Leak location.

The array provides detection for all leak types and provides a verification means which eliminates false alarms.
Figure 6a shows three variations of tidal movement. These tidal movements are ebb tide 60, which is the reverse tide in which the water level is lowered; flood tide 61 in which the water level is raised and slack water 62, which is the state of the tide turning between ebb and flood tides and vice versa.
Figure 6b shows a submerged sensor node 2, sonar detection signal 66, a leak comprising bubbles 63, a leak comprising dissolved CO2 molecules 64, the movement of the ebb tide moving away from the sensor node 2 is indicated by arrow 67 and the movement of the ebb tide moving towards the sensor node 2 is indicated by arrow 68.
In use, the sonar signals 66 detect bubbles 63 but cannot determine what the composition of the detected bubbles is. The ebb tide is moving away 67 from the sensor node 2 and its housed dissolved-gas sensor. Therefore, the gas sensor cannot detect any dissolved C02 molecules, which move in the same direction as the ebb tide.
When the tide switches direction to flood tide 68, the dissolved-gas sensor will detect and confirm the presence of dissolved CO2 as it flows towards and through the sensor node 2. When combined with the aquadopp [TM] tide current and pressure sensor, the location of the dissolved CO2 can be determined along with current tide direction and velocity.
Figure 7 shows a submerged sensor node 2, a gas detection sensor 31, H2O water molecules 72, CO2 carbon dioxide molecules 71, sonar signals 66, CO2 bubbles 63, dissolved H2O and CO2 molecules 64, ebb tide direction 60, flood tide direction 61, slack water 62 and detected CO2 Parts Per Million [PPM] detected data pattern 70. The signal 73 from the aquadopp [TM] tide current and pressure sensor provides current direction and velocity across the water column.
In use, the gas detector 31 housed within the submerged senor node 2 detects water H20 72 and carbon dioxide CO2 71 molecules that enter its detection chamber.
The dissolved molecules 64 can move along the same direction as the ebb tide 60, the same direction as the flood tide 61 and slack tide 62. Thus, the dissolved-gas sensor 31 and aquadopp [TM] tide current and velocity sensor provide the location, composition and concentration levels of dissolved CO molecules that match current tidal flow direction and velocity.
The data generated by the dissolved-gas sensor will show an increasing and then subsequently decreasing CO2 PPM distribution patterns 70 that match the ebb and flow timings detected by the aquadopp [TM] tide current and pressure sensor.
Figure 8 shows a graphical user interface [GUI], for the received processed data. GUI comprises user dialogue information fields, which are generated from the data received from the overhead satellite communication device. The user dialogue fields are:

A real time data logging screen for CO2 monitoring - home screen, which is generally indicated by arow 80;
System locations on the sea floor, with current direction 81;
Measured data metrics for each site location [each sensor node] 82;
Measured methane levels for each site location [each sensor node] 83, and;
Measured CO2 levels of each site location [each sensor mode] 84.

In use, the monitoring software will be generic so that it can be used on multiple monitoring projects. Each project will then require its own individual inputs to make it unique to the current monitoring project. The data provided by the GUI is unique to the system's location on the sea floor. Each storage site will require baseline measurements as each site will potentially have naturally occurring levels of CO2 present, once the baseline has been monitored and measured the software can be configured to set CO2 alarms above this threshold.
Also on this screen, the threshold level of activating a CO2/methane alarm can be determined and set accordingly. This alarm threshold will be based upon scientifically proven research, which includes baseline studies of the monitored sub marine area.
Depending upon the size of the storage zone and its distance between each monitoring system, it is possible that the base line surveys and therefore the associated alarm points may vary from site to site. An alarm will be triggered if this threshold level is passed. This GUI will be password protected to ensure that any edits/amendments cannot be made to the system, unless they are authorised accordingly.
Each node in the array can also support other sensor types utilising the node's power and data transmission systems. Compilatory sensor types may include permanently installed subsurface seismic sensors which the node can power up when an energy source is deployed in the water in order to assess the subsurface condition state on a regular basis.

Claims

A method of detecting a CO2 leak from a seabed comprising the steps of:
● Submerging a monitoring structure which houses a sensor array which further comprises a sonar sensor, a tidal direction and velocity sensor and a dissolved-gas sensor;

● Transmitting a sonar signal from said sonar sensor, which is suitable for detecting a CO2 gas bubble rising from a seabed;

● Transmitting a second signal from said tidal direction and velocity sensor, which is suitable for detecting the direction and velocity of a tide flow;

● Testing the tidal water about said dissolved-gas sensor, which sensor is suitable to detect dissolved CO2 molecules;

● Generating data which comprises data generated by said sonar sensor, said tidal direction and velocity sensor, and dissolved-gas sensor.

● Transmitting said CO2 data for said monitoring structure to a processing means to determine a CO2 leak and its location on the seabed.
A method according to claim 1 comprising the further step of:
• Detecting a submarine sound indicative of a gas bubble rising from a seabed with a hydrophone device comprised within said sensor array.
A method according to claims 1 or 2 further comprising the step of:
● generating data indicative of a C'.02 level detected by said dissolved-gas sensor and a tidal direction and velocity detected by said direction and velocity sensor.
A method according to claims 2 or 3 further comprising the step of:
● Generating data indicative of a gas bubble detected by said sonar sensor and an audible vibration detected by said hydrophone device.
A method according to any of the proceeding claims further comprising the step of
• Tethering a buoy device to said monitoring structure via an umbilical attachment means.
A method according to any of the proceeding claims further comprising the step of
• Communicating electrical power and data communications between said buoy device and said sonar sensor, said tidal direction and velocity sensor, said dissolved-gas sensor and said hydrophone device, via said umbilical means.
A method according to any of the preceding claims further comprising the step of
• communicating said data indicative of CO2 location on seabed from said buoy, to a satellite communication device via a wireless satellite communication means.
A method according to any of the preceding claims wherein a plurality of said monitoring structures are arranged in a CO2 detection array on a seabed.
A method according to any of the preceding claims further comprising the step of
• generating an alarm means on a user interface which is indicative of detected CO2 that exceeds a predetermined level.
A CO2 monitoring structure suitable in accordance with the method of the preceding claims for detecting a CO2 leak from a seabed, comprising a sensor array housed within said structure; wherein said array further comprises sonar sensor, a tidal direction and velocity sensor and a dissolved-gas sensor.
A structure according to claim 10 further comprising a hydrophone device.
A structure according to claims 10 or 11 further comprising an attachment means suitable for providing an operable connection to a tether device.
A structure according to claim 12 wherein the attachment means comprises a multicore elongate body further comprising an electrical cable and/or an optical fiber.
A buoy device attached to said structure in accordance with claims 10 to 13; and said structure being used in said method in accordance with claims 1 to 9, further comprising:
• an attachment means for providing an operable connection to tether device,

• A rechargeable battery cell operably connected to an external solar panel array,

• A satellite communication means operably connected to said sensors of said monitoring structure, which in use communicates with a satellite telemetry system.
A user interface used in said method in accordance with claims 1 to 9 further comprising:
• Means of processing data indicative of detected CO2 and determining the CO2 source relative to said monitoring structure.

• An alarm means which activates when the detected CO2 exceeds a predetermined level.