GB2580660A

GB2580660A - Pressure sensor

Info

Publication number: GB2580660A
Application number: GB1900810.1A
Authority: GB
Inventors: Merciu Ioan-Alexandru
Original assignee: Equinor Energy AS
Current assignee: Equinor Energy AS
Priority date: 2019-01-21
Filing date: 2019-01-21
Publication date: 2020-07-29
Also published as: GB201900810D0

Abstract

A pressure sensor 2 comprising a curved or cylindrical membrane 3 comprising an outer graphene layer (fig 2, 4a) arranged over a carbon nanotube layer (fig 2, 5). The membrane 3 may also comprise an inner graphene layer (fig 2, 4b) beneath the carbon nanotube layer (fig 2, 5). The membrane 3 may further comprise a neural culture layer (fig 2, 6), a neuron hybrid nuclear plate (fig 2, 7) and/or a plastic layer. The membrane may also further comprise further graphene and carbon nanotube layers. The pressure sensor may further comprise metal wires and/or a gyro sensor. The pressure sensor may be used in a borehole (fig 5, 13) drilling sub 1 or an intervention tool such as an LWD sub 1. The pressure sensor may be used in a method of detecting acoustic waves from a seismic source (fig 5, 11), storing the data, and deciding whether to drill for hydrocarbons.

Description

Pre sure Ssensor The present invention relates to the field of sensors. In particular, it relates-to the field of pressure sensors, e.g. for detecting acoustic (e.g. sonic or seismic) waves, particularly for use in the field of oil and gas.

In the oil and gas industry, it is known to acquire seismic data about:a subsurface region with a seismic tool. A seismic tool comprises a plurality of acoustic (e.g. seismic) sources (vibrating devices) and an array of acoustic (pressure) receivers. The array of receivers is placed at a particular distance from the sources. In some cases, the array of receivers is arranged azimuthally around a mandrel of the tool.

There area variety of seismic tools available on the market, both for use while drilling and wireline (post drilling). However, all of them employ the same operating principle: an acoustic (e.g. seismic)/pressure wave is generated by the sources; the pressure perturbance propagates in all directions though the surrounding media, interacts with the environment; and some perturbances are recorded by the receiver array.

The pressure perturbance(s) may be recorded by one receiver element over a period of time and in such a case a full waveform will be digitalized and sampled by the DSP (downhole seismic processor) electronics.

The waveforms can be processed using a plurality of signal processing methods and an answer is given to a question of the user based on an inversion process.

However, the wave fronts inside the borehole fluids (usually but not necessarily liquid phase) are sampled at the positions of the receivers and this presents a strong limitation on both spatial and time signal processing migration.

Thus, it is possible to sample the, pressure perturbation but, only locally and this imposes large errors into the analysis (typically a discrete Fourier transform analysis) of the data.

In addition, with these known seismic tools, it is not possible to sample the entire acoustic field azimuthally around the tool body and it is not possible to detect correctly the azimuthal amplitude variation. Therefore, the deep formation or structure image is incomplete and/or incorrect.

In view of the above, there is a need for an improved seismic tool. According to a first aspect of the invention, there is provided a pressure sensor comprising a membrane, wherein the membrane comprises: a. an outer graphene layer; and b. a carbon nanotube layer; wherein the, grapinene layer is arranged over the carbon nanotube layer and the membrane has a curved or substantially cylindrical shape.

Thus, the pressure sensor comprises a curved or (preferably) substantially cylindrical membrane, which allows the sensor to detect and measure pressure (e.g. detect acoustic waves such as sonic or seismic waves) azimuthally about an axis. In a preferred embodiment, the membrane is arranged such that it can detect pressure waves (e.g. acoustic waves such as sonic or seismic waves) over a full 360° about an axis. As such, pressure'waves may be detected simultaneously at all angles over a full 360° about an axis.

As a graphene layer and a carbon nanotube layer are used to measure pressure (e.g. detect acoustic waves such as sonic or seismic waves), measurements may be made with a very fine resolution. This is mainly due to the very small size of the carbon nanotubes and, thus, how closely they may be spaced. For example, the carbon nanotube layer may comprise carbon nancrtubes with a spacing of 1 mm or less, 0.8 mm or less, 0.6 mm or less, 0.5 mm or less, 0.4 mm or less, 0.3 mm or less, 0.2 mm or less, 0,1 mm or less, 0.08 mm or less, 0.06 mm or less. 0.05 mm or less, 0.04 mm or less, 0.03 mm or less, 0.02 mm or less, and preferably 0.01 mm or less.

The carbon nanotube layer preferably comprises an array of carbon nanotubes. The carbon nanotubes may be arranged in a regular or irregular arrangement. Each carbon nanotube is preferably arranged substantially perpendicularly to the outer graphene layer (e.g. the longitudinal axes of each or some carbon nanotube is preferably perpendicular to the surface of the outer graphene layer). In some embodiments, each carbon nanotube, or some carbon 30== nanotubes, may be arranged such that their longitudinal axes are at an angle to the surface of the outer graphene layer, wnerem the angle is preferably between around 45' and around 90°, for example.

Outer ends of the carbon nanotubes may be attached to the outer graphene layer, for example with glue. For example, an epoxy glue may be used. Preferably, the glue is resistant to (i.e. does not degrade under) high temperatures such as those that may be found in a borehole. In some embodiments, titanium-based glue (glue comprising titanium) may be used.

In some embodiments, the carbon nanotubes are not attached to the outer graphene layer (e.g. with glue), i.e. the carbon nanctubes are not formed separately and then attached to the outer graphene layer, but rather the carbon nanotubes are grown from the outer graphene layer, e g. such that the outer graphene Layer and the carbon nanotubes form an integral component.

The outer graphene layer is preferably the outermost layer of he membrane.

The (any) graphene layer preferably has a thickness of one atom. This can help to minimise the overall thickness of the membrane, such that further components may be provided (may ft) inside an inner diameter of the membrane (e.g. as described below).

The carbon nanotube layer may be around 10 to 15 atoms thick, for

example.

The graphene layer (and any further graphene layer provided, e.g. as described below) and the carbon nanotube layer may have a combined thickness of around 1-5 ''.mm, and preferably around 2 mm, for example.

Graphene layers are strong but flexible. They are also resistant to corrosion and high temperatures and pressures, such as can be found in a borehole. This makes them a good choice for use in the membrane.

When the outer graphene layer experiences or receives an acoustic wave (e.g. a sonic or seismic wave), it is preferably arranged such that it deforms or moves in response to the wave. The carbon nanotubes in the carbon nanotube layer are preferably arranged such that, as the outer graphene layer flexes arid bends in this way, the carbon nanotubes are stretched and/or compressed. This may cause an electrical current to be induced in the carbon nanotubes, which is related to (e.g. proportional to) the movement of the outer, graphene layer, i.e. the amplitude of the acoustic wave received_ The electrical signal induced in the carbon nanotube layer is then preferably transferred to electronics and/or a processing/computing device for recording, processing and/or analysis, for example.

The membrane may further comprise an inner graphene layer provided beneath the carbon nanotube layer. Inner ends of the carbon nanotubes may be attached, e.g5 with glue, to the inner graphene layer. Alternatively, e.g. as described above, the carbon nanotubes may be grown from the inner graphene layer.

In some embodiments, the, membrane may further comprise a neural culture layer provided, for example, beneath the carbon nanotube layer or an inner graphene layer, if provided. In this case, the, membrane may further comprise a neuron hybrid nuclear plate provided beneath the neural culture layer. The neural culture layer, and optional neuron hybrid nuclear plate, may allow electrical current induced'in the carbon nanotube layer to be transferred to electronics and/or a processing/computing device for recording, processing and/or analysis, for

example.

The neuron culture layer is preferably formed of an artificial neuron culture, which may be pre-trained for data transmission, e.g. to the neuron hybrid nuclear plate.

The neuron hybrid nuclear plate may be a base plate formed of cells of agglomerated neurons to which neurons in the neuron culture layer are (may be) connected.

An electrical (data) signal may be transferred from the carbon nanotube layer, through an inner graphene layer (if provided) and neuron culture layer to the neuron hybrid nuclear plate. The neuron hybrid nuclear plate may be connected to electronics and/or a processing/computing device for recording, processing and/or analysis e.g. by standard data wires or cables (e.g. metal (copper) wires or fibre optic cables).

Using a neuron culture layer, and optionally a neuron hybrid nuclear plate can result in a space saving compared, for example, with more conventional data transmission connections (e.g. copper wires) being used.

In some embodiments (e.g. where an inner graphene layer and/or neuron culture layer and neuron hybrid nuclear plate are not provided), the membrane may comprise a plastic layer arranged beneath the carbon nanotube layer. The plastic layer may comprise an array of capacitive or conductive dots, with each carbon nanotube preferably being connected to a capacitive or conductive dot in the plastic layer. Wires, e.g. metal (copper) wires, may be connected to an underside of plastic layer (e.g. preferably an underside of the rcapacitive or conductive dots) and may be arranged to transfer an electrical signal from the carbon nanotube layer to, e.g., a processor or other device.

In some embodiments, the membrane may further comprise a second pair cf graphene layer and carbon nanotube layer arranged under the outer graphene layer and carbon nanotube layer. In other words, the membrane may comprise more than one (e.g. two) pairs of graphene layer and carbon nanotube layer. Each pair of graphene layer and carbon nanotube layer may be separated by a layer, e.g. of silicone.

The pressure sensor may have an axial length of around 0.5 -2 m, particularly around 1 m.

The pressure sensor may have an outer diameter of around 0.1 to 0.3 m, for

example.

The pressure sensor preferably comprises a gyro sensor. For example, a gyro sensor may be provided in a neuron hybrid nuclear plate, if provided.

According to a second aspect, there is provided a drilling sub suitable for use in a borehole comprising a pressure sensor as described above. As mentioned above, the pressure sensor of the first aspect is particularly well-suited for use in a borehole. This is due partly to its cylindrical shape. Also, it has an outer layer made of graphene which can withstand he kinds of environmental conditions found in borehole& A drilling sub may also or alternatively be referred to as a drilling tool.

The drilling sub preferably comprises a processor (e.g. a DSP) and the membrane, is preferably connected to the processor for processing data recorded by the pressure sensor. The processor is preferably provided within an inner diameter of the membrane.

The drilling sub may comprise a computer (e.g. a computer interrogator and translator), which is also preferably provided within an inner diameter of the membrane. The processor is preferably connected to the computer.

The pressure sensor and other components of the drilling sub are preferably arranged such that when the membrane experiences a pressure wave, data representing that wave is transferred from the membrane, to the processor and preferably on to a computer. Data generated at the computer may then be transferred to one or more surface computers or memory.

The drilling sub may be a logging while drilling (LWD) sub, for example. The drilling sub is preferably substantially cylindrical and may contain the pressure sensor in a section thereof. The pressure sensor comprises a membrane, as described above, which is preferably arranged or wrapped circumferentially around a section of the drilling sub. Preferably, the membrane is arranged around an entire circumference of the drilling sub.

The pressure sensor (or membrane) may cover an axial length of the drilling sub of around 0.5 -'2 m, particularly around 1 m, for example.

In some embodiments, a plurality of pressure sensors may be provided spaced along an axial length of the driving sub, for example. The plurality of pressure sensors may cover an axial length of the drilling sub of around 2 to 6 m, e.g. around 4 m.

The drilling sub and pressure en or(s) may have an outer diameter of around al to 0.3 m, for example.

The drilling sub may be incorporated into a drill string, e.g. above or below an acoustic (seismic) source. As such, a further aspect of the invention relates to a drill string comprising a drilling sub as described above, e.g. and preferably with one or more acoustic (e.g. seismic) sources. The drill string may comprise a plurality of, e.g. axially spaced, drilling subs, e.g. as described above.

The acoustic source may be arranged to emit waves with a frequency of from around 500 Hz and/or up to around 10 MHz, for example.

According to a further aspect, there is provided a detector comprising a pressure sensor as described above. The detector may be a pressure wave detector or an acoustic pressure wave detector, for example. The detector may be arranged or adapted to detect pressure waves transmitted through a fluid (e.g. oil or gas) column, for example. The detector may be suitable for use in a surface location The detector preferably comprises a processor and the membrane is preferably connected to the processor for processing data recorded by the pressure sensor. The processor is preferably provided within an inner diameter of the membrane.

The detector may comprise a computer (e.g. a computer interrogator and translator), which is also preferably provided within an inner diameter of the membrane. The processor is preferably connected to the computer.

The pressure sensor and other components of the detector are preferably arranged such that when the membrane experiences a pressure wave, data representing that wave is transferred from the membrane, to the processor and preferably on to a computer. Data generated at the computer may then be transferred to one or more surface computers or memory.

The detector is preferably substantially cylindrical and maycontain the pressure sensor in a section thereof. The pressure sensor comprises a membrane, as described above, which is preferably arrangedr or wrapped circumferentially around a section of the detector. Preferably, the membrane is arranged around an entire circumference of the detector.

The pressure sensor (or membrane) may cover an axial length of the detector of around 0.5 -2 m, particularly around 1 m, for example.

In some embodiments, a plurality of pressure sensors may be provided spaced along an axial length of the detector, for example. The plurality of pressure sensors may cover an axial length of the detector of around 2 to 6 m, e.g. around 4 m.

The detector and pressure sensor(s) may have an outer diameter of around 0.1 to 0.3 m, for example.

According to a further aspect, there is provided an intervention tool comprising:a pressure sensor as described above. The intervention tool may be suitable for use in bore holes which have already been drilled, for example. One example of an intervention tool is a LWD tool such as a multipole LWD sonic tool which makes acoustic velocity measurements during drilling (e.g. of a well).

The intervention tool preferably comprises a processor and the membrane is preferably connected to the processor for processing data recorded by the pressure sensor. The processor is preferably provided within an inner diameter of the membrane.

The intervention tool may comprise a computer (e.g. a computer interrogator and translator), which is also preferably provided within an inner diameter of the membrane. The processor is preferably connected to the computer.

The pressure sensor and other components of the intervention tool are preferably arranged such that, when the membrane experiences a pressure wave, data representing that wave is transferred from the membrane, to the processor arid preferably on to a computer. Data generated at the computer may then be transferred to one or more surface computers or memory_ The intervention tool is preferably substantially cylindrical and may contain the pressure sensor in a section thereof. The pressure sensor comprises a membrane, as described above, which is preferably arranged or wrapped circumferentially around a section of the intervention tool. Preferably, the membrane is arranged around an entire circumference of the intervention tool.

The pressure sensor (or membrane) may cover an axial length of the intervention tool of around 0.5 -2 m, particularly around 1 m, for example.

In some embodiments, a plurality of pressure sensors may be provided spaced along an axial length of the intervention tool, for example. The plurality of pressure sensors may cover an axial length of the intervention tool of around,2 to 6 m, e,g. around 4 m.

The intervention tool and pressure sensor(s) may have an outer diameter of around 0.1 to 0,3 m, for example.

The acoustic source may be arranged to, emit waves with a frequency of from around 500 Hz and/or up to around 10 MHz, for example.

A further aspect of the invention relates to a method of detecting acoustic waves, the method comprising: a= emitting acoustic waves with an acoustic source; and detecting the acoustic waves with a pressure sensor as described above.

The method preferably also comprises recording data representing the detected acoustic waves (e.g. in a memory), and further preferably storing, processing and/or analysing the recorded data.

The acoustic source may be a seismic or sonic source, for example, and the method may be performed in a borehole, for example.

The pressure sensor may be provided in a drilling sub, a detector and/or an intervention tool, for example as described above.

A further aspect of the invention relates to a method of acquiring seismic data, the method comprising performing the method described above and storing data representing the detected acoustic waves in a memory.

A further aspect of the invention relates to a method of prospecting for hydrocarbons, the method comprising performing the method described above; 30= processing the acquired seismic data, and making a decision about whether and/or where to drill for hydrocarbons based on the processed seismic data.

A further aspect of the invention relates to use of a pressure sensor as defined above in an oil and gas application, e.g. for acquiring seismic data and/or prospecting for hydrocarbons, Embodiments of the present invention use sensitive graphene based piezoelectric pressure membranes as pressure sensors, which may be wrapped around drilling (e.g. LWD) subs as acoustic receivers.

In some preferred embodiments, wires connecting base layers of the sensor to electronics may be replaced with a neural culture, which may be (have been) trained for data transmission, for example.

Embodiments of the present invention, e.g. as described above, may provide the following advantageous features: - the possibility to record an entire wavefield of acoustic (e.g. sonic/ultrasonic) and associated modes azimuthally around a drilling sub at a high discrete spatial sampling rate; - the use of neural transmitters attached to specific points on the membrane can provide the capability to record long waveforms without electronic cross talking; the ability to measure the vvavefield at all angles at the same time can provide a complete free rotation alignment of the traces; the increased sampling rate can eliminate or significantly reduce he uncertainty of full waveform records; the use of an azimuthal array of ultrasonic transmitters can eliminate the need (e.g, in the prior art) to rotate ultrasonic receivers (e.g. in wireline applications).

Embodiments of the present invention may be used in various oil and'gas applications such as oil and gas drilling applications, and their use may: enhance full waveform borehole image techniques on LWD; enhance and provide full azimuthal coverage for near borehole d ep formation imaging; - facilitate formation illumination and geosteenng in real time, - provide enhanced data input for geosteering; e.g. when used in combination with EM methods; provide early detection of lateral extension of specific geological layers, which can reduce the lost time due to mud losses in weak formations; - detect a gas-oil contact visible in a seismic wavefield; - enhance all current applications on seismic tools; facilitate a full reaiization of Full Waveform Sonic (FWS) techniques. In addition, embodiments of the pressure sensor according to the present invention may be used in numerous possible medical applications, such as: - use in an (e.g. artificial intelligence) ultrasonic bra, for example for detecting possible tumours and thereby potentially reducing the number of patients exposed to x-ray based mammography techniques; - use of neural transmission in an artificial bra.

Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Fig, 1 is a partially cut-out cross-sectional view of an embodiment of a LWD sub; Fig, 2 is a cross-sectional view of an embodiment of a membrane; Fig. 3 is a schematic diagram illustrating data transfer connections in an embodiment; Fig. 4 is a partially cutaway cross-sectional view illustrating the placement of electronic components inside a drilling sub; Fig. 5 is a schematic diagram illustrating a drilling sub in a borehole with acoustic wave propagation; Fig. 6 is a horizontal cross-sectional view of he drilling sub in a hole at membrane level; Fig. 7 is a schematic diagram showing the variation of incoming amplitudes azimuthally around the drilling sub; and Figs. BA and BB are graphs showing simulated recorded data according'to an embodiment of the invention and real recordeddata using a prior art sensor, respectively.

Fig. 1 shows a partially cut-out cross-sectional view of a LWD sub '1 according to an embodiment. The LWD sub 1 can be incorporated into a drill string above or below an acoustic source (not shown).

The acoustic, source is arranged to emit acoustic waves with a frequency of from around 500 Hz up to around 10 MHz., The LWD sub 1 is substantially cylindrical and contains an acoustic sensor 2 in a section thereof. The acoustic sensor 2 comprises a membrane 3 which is arranged or wrapped circumferentially around a section of the LWD sub 1. The sensor 2 (or membrane 3) covers an axial length of the sub 1 of around 1 m.

In some embodiments, a plurality of acoustic sensors 2 are provided spaced along the length of the LWD sub 1. The plurality of acoustic sensors 2 can cover an axial length of the sub 1 of around 4 m. 11 -

The LWD sub 1 and acoustic sensor(s) 2 have an outer diameter 0 Li n d 0 to 0,3 ne In use, a plurality of D subs 1 can be used, one on top of the other, down a borehole.

Fig. 2 is a cross-sectional view of part of a membrane 3 according to an embodiment. The membrane 3 comprises five layers 4a, 5, 4b 6, 7 An outer graphene layer 4a is provided as the outermost layer of the membrane 3, A layer of carbon nanotubes 5 is provided beneath the outer graphene layer 4a.

The carbon nanotube layer 5 is formed from an array of carbon nanotubes, each arranged substantially perpendicularly to the outer graphene layer 4a. Outer ends of the'carbon nanotubes are attached with glue to the outer graphene layer 4a In an alternative embodiment, the carbon nanotubes are grown from the outer graphene layer 4a. The carbon nanotubes in the carbon nanotube layer 5 have a spacing of around 0.01 mm.

In the embodiment shown in Fig. 2, a second, inner graphene layer 4b is provided beneath the carbon nanotube layer 5. Inner ends of the carbon nanotubes are attached with glue to the inner graphene layer 4b.

The graphene layers 4a, 4b each have a thickness of one atom. The carbon nanotube layer 5 is around 10 to 15 atoms thick, such that the graphene layers 4a, 4b and carbon nanotube layer 5 have a combined thickness of around 2 mm.

T graphene layers 4a, 4b are strong but flexible They are also resistant to corrosion and high temperatures and pressures, such as can be found in a borehole.

When the outer graphene layer 4a experiences or receives a pressure (acoustic) wave, it deforms or moves in response to the wave. As the outer graphene layer 4a flexes and bends in this way, the carbon nanotubes in the carbon nanotube layer 5 are stretched andfor compressed. This causes an electrical current to be induced in the carbon nanotubes, which is related (e.g, proportional) to the movement of the outer graphene layer 4a, i.e. the amplitude of the wave.

The electrical signal induced in the carbon nanotube layer 5 is, then transferred to electronics for recording, processing and analysis, One way in which the electrical current induced in the carbon nanotube layer 5 can be transferred to electronics is shown in the embodiment of Fig. 2. Here, beneath the inner graphene layer 4b, a neuron culture layer 6 is provided, with a neuron hybrid nuclear plate 7 being arranged beneath the neuron culture layer 6. The neuron culture layer 6 is formed of an artificial neuron culture, which is pre-trained for data transmission to the neuron hybrid nuclear plate 7. The neuron hybrid nuclear plate 7 is a base plate formed of cells of agglomerated neurons to which the neurons in the neuron culture layer 6 are connected. An electrical signal can be transferred from the carbon nanotube layer 5, through the inner graphene layer 4b and neuron culture layer 6 to the neuron hybrid nuclear plate 7.

In an alternative embodiment, rather than the inner graphene layer 4b, neuron culture layer 6 and neuron hybrid nuclear plate 7, a plastic plate or layer with capacitive or conductive dots is provided beneath the carbon nanotube layer, with each capacitive or conductive dot being connected to a carbon nanotube in the carbon nanotube layer 5. Copper wires are connected to the underside of the capacitive or conductive dots and are arranged to transfer the electrical signal from the carbon nanotube layer 5 to a processor.

In some embodiments, the membrane 3 comprises more than one (e.g. two) pairs of outer graphene layer 4a and carbon nanotube layer 5, with each pair of outer graphene layer 4a and carbon nanotube layer 5 being separated by a layer of silicone.

Fig. 3 is a schematic diagram illustrating the data transfer connections between the membrane 3, a DSP 8, and a final computer interrogator and translator 9. As can be seen in Fig. 3, when the membrane 3 experiences a pressure wave 10, data representing that wave 10 is transferred from the membrane 3, to the DSP 8 for signal processing, e.g. as known in the art, and on to a computer 9 for further processing and/or analysis.

As shown in Fig. 4, the DSP 8 and computer 9 are located within an inner diameter of the membrane 3. Data generated at the computer 9 is transferred to one or more surface computers or memory (not shown).

Fig. 5 shows a drilling sub 1 in a borehole 13. The drilling sub 1 comprises a seismic source 11 and a 10 kHz absorbent 12 provided beneath the acoustic sensor 2. The drilling sub directly transmits the 10 kHz signal along its body and this can destructively interfere with other signals. The 10 kHz absorbent 12 filters -13 -out this direct signal from the source to receiver in anydrilling subs and thereby protects the usable signal (the signal of interest).

The borehole 13 is in a subsurface region 15 and is filled with borehole fluid 14. The source 11 emits acoustic (seismic) waves which travel through and interact with the subsurface 15 and borehole fluid 14. Waves which are reflected back towards'the sub 1 are detected by the sensor 2. As the waves travel through the subsurface region 15 and borehole fluid 14, their form may be changed depending on the structure of the material through which they pass. In the example shown in Fig. 5, regions A-F contain the following wave types: A -P-wave B -S-wave C -Stoneley mode D -Stoneley mode E S-wave F -P-wave Regions A-C are located in rock and regions D-F are lac ed in the borehole fluid 14.

Fig. 6 shows a horizontal cross-section through the sub 1 showing how seismic waves 10 can arrive at the membrane 3 from different directions. As such, there will be a variation in the amplitudes detected azimuthally around the sub 1.

This variation can be detected by the sensor 2 as a gyro sensor is incorporated in the neuron hybrid nuclear plate 7.

Fig. 7 shows how amplitudes of pressure waves 10a arriving at he membrane 3 can vary azimuthally around the membrane 3.

Fig. 8A and B show two-dimensional (time versus azimuthal angle around the sub) plots of amplitude plotted of for: Fig. 8A --a numerical simulation of an embodiment with amembrane: with carbon nanotubes with 1 mm spacing; Fig. 88 -real data using the most advanced prior art sensors.

As can be seen from Figs. 8A and 8B, the invention (Fig. 8A) provided a much better sampling resolution than that which can be obtained with the most advanced prior art sensors. The most advanced prior art sensors do not capture the details of the full wave field but provide only a very sparse sampling.

Claims

-14 -Claims 1. A pressure sensor comprising a membrane, wherein the membrane comprises: a. an outer graphene layer; and b. a carbon nanotube layer; wherein the graphene layer is arranged over the carbon nanotube layer and the membrane has a curved or substantially cylindrical shape.
2. A pressure sensor as claimed in claim 1, wherein the membrane further comprises an inner graphene layer provided beneath the carbon nanotube layer.
3. A pressure sensor as claimed in claim 1 or 2, wherein the carbon nanotube layer comprises carbon nanotubes with a spacing of 0.5 mm or less, preferably 0.01 mm or less.
4. A pressure sensor as claimed in claim 1, 2 or 3, wherein the membrane further comprises a neural culture layer provided beneath the carbon nanotube layer or an inner graphene iayer, if provided,
5. A pressure sensor as claimed in claim 4, wherein the membrane further comprises a neuron hybrid nuclear plate provided beneath the neural culture layer.
6. A pressure sensor as claimed in claim 1, 2 or 3, wherein the membrane further comprises a plastic layer beneath the carbon nanotube layer.
7, A pressure sensor as claimed in claim 6, wherein metal wires are connected to an underside of the plastic layer.
A pressure sensor as claimed in any preceding claim, the membrane further comprising a further graphene layer and carbon nanotube layer arranged under the outer graphene layer and carbon nanotube layer.
9. A pressure sensor as claimed in any preceding claim, further comprising a gyro sensor.
10. A drilling sub for use in a borehole comprising a pressure sensor as claimed in any preceding claim,
11. A drilling sub as claimed in claim 10, wherein the membrane is connected to a processor for processing data recorded by the pressure sensor.
12. A detector comprising a pressure sensor as claimed in any of claims 1 tog.
13. A detector as claimed in claim 12, wherein the membrane is connected to a processor for processing data recorded by the pressure sensor.
14. An intervention tool comprising a pressure sensor as claimed in any of claims 1 to 9.
15. An intervention tool as claimed in claim 14, wherein the membrane is connected to a processor for processing data recorded by the pressure sensor.
16. A method of detecting acoustic waves, the method comprising: a emitting acoustic waves with an acoustic source; and b. detecting the acoustic waves with a pressure sensor as claimed in any of claims 1 to 9.
17. A method as claimed in clam 16, wherein the acoustic source is a seismic source and the method is performed in a borehole.
18. A method as claimed in claim 16 or 17, wherein the pressure sensor is provided in a drilling sub as claimed in claim 10 or 11, a detector as claimed in claim 12 or 13, or an intervention tool as claimed in claim 14 or 15.
19. A method of acquirina seismic data, the method comprising performing the method of any of claims 16 to 18 and storing data representing the detected acoustic waves in a memory.
20. A method of prospecting for hydrocarbons, the method comprising: a. performing the method of claim 19; b. processing the acquired seismic data; and c. making a decision about whether and/or where to drill for hydrocarbons based on the processed seismic data. 25