RU2724964C1 - Digital recording module for underwater research - Google Patents

Abstract

FIELD: measurement technology.SUBSTANCE: invention relates generally to geophysical measurement systems, and specifically to seismic technologies for data collection and sensors. Invention is capable of simultaneously recording seismic and acoustic signals, realizing the seismic waves separation principle depending on the propagation direction. Technical solution is capable of receiving, digitizing, processing of accumulating or transmitting a recorded seismic-acoustic array of measurements. Invention can be used as an independent measuring complex, and as part of bottom braids, by means of cables being connected in series into a single measuring circuit. Invention can be used to solve tasks of seismic exploration in transit zones and on shelf, seismic and acoustic observations of water areas, monitoring of underwater in that situation, including in arctic region, etc.EFFECT: invention provides improved quality of measurement data owing to use of a unique component base, molecular-electronic geophones as linear motion sensors and molecular-electronic hydrophones as sensors for recording an acoustic field in a medium; including invention reduces existing mass and dimensions parameters while maintaining high signal-to-noise ratio of device.8 cl, 7 dwg

Description

The invention relates generally to geophysical measuring systems, and specifically to seismic data acquisition technologies and sensors. It can be used to solve seismic problems in transit zones and on the shelf, seismic and acoustic observations of water areas, monitoring underwater conditions including those in the Arctic region, etc.

Oil-based products are widely distributed in the modern economy and can be found in all sectors: from gasoline to medical devices, children's toys and a wide range of everyday items. To meet the constant demand for these products, oil and gas reserves must be explored and explored in a timely manner so that these important resources can be effectively managed. As a result, there is a continuing need for new seismic sensor systems and new exploration technologies. Scientists and engineers typically use seismic exploration based on transmitted and reflected waves to discover new oil and gas reservoirs, as well as to explore and manage existing reserves during field development. Seismic exploration is carried out by placing an ordered array of seismic sensors and acoustic sensors in the study area and monitoring the response to a controlled effect on the ground through seismic sources such as vibrators or air guns, or explosive detonation. The response of the reflected signals depends on the geology of the internal structure of mineral reservoirs and other underground formations, which allows you to get an image of the corresponding structures. Conventional marine seismic surveys are carried out by towing an array of seismic sensors or receivers behind a research vessel, the receivers being distributed along one or more hoses. A set of air guns or other seismic sources is used to excite seismic waves that propagate through the water column and penetrate the ocean floor. The signal is partially reflected from subsurface structures, returned through the water column and recorded by an array of meters. As an alternative, seismic receivers can also be located along the cable at the bottom of the reservoir or function as separate autonomous seismic nodes distributed on the seabed. Seismic receivers include both pressure sensors and motion detectors, which can be provided as separate components or combined with both types of sensors located in close proximity to the receiver module or seismic assembly. For example, a set of pressure sensors can be configured into an array of hydrophones and adapted to record scalar pressure measurements of a seismic wave field propagating through a water column or other seismic medium. Motion sensors include accelerometers and geophones, which can provide uniaxial or three-dimensional vector measurements of velocity or acceleration, characterizing the movement of the medium in response to the propagation of seismic waves. Geophysical data related to underground structures are obtained by observing reflected seismic waves using an array of such receiving components. The obtained seismic signals can be used to form an image characterizing the composition and geology of the subsoil in and around the study area. The overall image quality depends on the sensitivity and noise of the receiving devices, which creates a demand for more advanced sensors and receiving technologies.

The quality of the data obtained largely depends on the sensitivity of the sensors used, in particular hydrophones. Most hydrophone designs use a piezoelectric sensor. The piezoelectric sensitive element has a low conversion coefficient, a relatively high intrinsic noise in the low-frequency region, and a limited frequency range.

These disadvantages can be overcome if instead of using a piezoelectric, use a molecular-electronic sensitive element. In the scientific literature, solutions using molecular-electronic geophones are described in [1,2], and hydrophones in [3,4]. In patent RU 2687297 C1 a basic model of a low-frequency two-component bottom braid using highly sensitive molecular-electronic geophones is presented, and also in patent RU 2678503 the structure and principle of operation of a molecular-electronic hydrophone are presented. The disadvantage of the technical solution for the molecular-electronic hydrophone, presented in patent RU 2678503, is the strong dependence of sensitivity on immersion depth, which does not allow its use in the composition of the bottom spit described in RU 2687297 C1 and designed to work on the bottom, where the typical working depth is from 10 to 100 meters, and, in some cases, can reach 500 meters. A technical solution for increasing the working depth is proposed in RU 2696060 C1, where it is proposed to use a housing filled with an easily compressible liquid instead of a gas bubble as a reference volume. This solution allows you to significantly increase the working depth to the required 500 meters. However, the high sensitivity of the hydrophone is achieved by using a large volume of compressible fluid ~ 1 liter. The use of such a hydrophone as part of the modules of the digital bottom braid significantly increases the dimensions and weight of the modules and makes their use inconvenient.

The patent base also contains numerous certificates for inventions related to the class of underwater cable systems (ocean bottom cable), seismic-acoustic measuring systems for seismic exploration located on the seabed and combined into long seismic streamers.

So, for example, in patent DK 178813 B1, a bottom cable spit is designed for seismic exploration of the bottom of the water area, consisting of measuring modules, these modules being separated from each other by separate sections of stressed elements, where each section of the stressed element has acoustic decoupling devices on each the end. In addition, each seismic measuring unit contains a removable autonomous sensor capsule for sensing and recording seismic data.

Another example is US 10274627 B2, which also presents the configuration of the modules of the bottom seismic streamer, characterized in that each module includes seismic and / or acoustic sensors suspended in an acoustic medium located between the dual module housing. In this case, the modules contain an analog-to-digital converter, internal memory, synchronization elements and a power source.

At the same time, the class of inventions that is similar in some applications to the proposed technical solution and is a class of separate autonomous seismic stations (ocean bottom station) is presented quite extensively.

So, for example, in patent US 005189642 A presents a device for recording acoustic and seismic signals on the ocean floor with minimal noise. The seismic recorder directly installs the measuring geophones to the bottom, has a data storage device, stores seismic data and can be removable. The seismic station is equipped with an ascent device and an anchor system.

A comprehensive bottom towed four-component antenna array for collecting seismic data is presented in US Pat. No. 6,607,050 B2 and consists of a four-channel electronic section for collecting seismic data, a three-component cardan gimbal and a hydrophone in the housing. The four-component station has a modular structure, and the signal is transmitted via cable to the central station. The inventors claim a high SNR, however, it is planned to achieve this high ratio only due to the compact cable connection and small dimensions of the antenna, which reduce interference during data transmission.

As a prototype of the claimed technical solution for the totality of signs, we take the invention described in patent US 10274627 B2. Among the disadvantages of the prototype, it is possible to single out, first of all, the weak sensitivity and high intrinsic noise of the meters used, while the prototype requires a strong and airtight housing to operate at significant static water pressures, which leads to significant prototype dimensions. Including the disadvantage of the prototype can be attributed to the limitation of functionality as a separate measuring module.

At the same time, the objective of the proposed technical solution is precisely the use of high-sensitivity and low-noise molecular-electronic meters of velocity fields [5] and acoustic pressures [6] to implement the principle of separation of seismic waves depending on the direction of propagation, collection, digitization and transmission of captured seismic-acoustic energy data transmitted and reflected waves, possible integration into a single chain of modules for constructing bottom braids, the ability to work at depths of up to 500 meters (the most interesting range for underwater seismic exploration), the ability to reduce weight and size requirements and the requirements for tightness of the hull.

The technical result of the proposed solution is to increase the sensitivity to external acoustic signals of digital recording modules of the bottom braid, through the use of highly sensitive molecular-electronic hydrophones. At the same time, the dimensions and weight of the device, as well as the working depth, correspond to modules using less sensitive piezoelectric hydrophones.

The problem is solved and the technical result of the invention is achieved by the fact that the digital recording module, designed to measure the vertical component of the seismic velocity field at the bottom of the reservoirs, as well as registering the acoustic pressure wave field in the medium, contains a housing consisting of two sections, and in the first section, filled with air, at least one molecular-electronic geophone is located, and in the second section, filled with an easily compressible liquid, there is a sensitive element of the molecular-electronic hydrophone, as well as electronic power, amplification and frequency correction boards, an ADC board and a microcontroller board, sections are isolated from each other by a spacer containing sealed wire contacts and a membrane open to the external environment. In particular cases of implementing the invention, the module contains a battery providing independent power supply to the module; the module contains an internal data storage device in the form of internal memory for autonomous recording of seismic-acoustic data; the module contains a network adapter that allows you to transfer, if necessary, the data recorded by the sensor to external devices. In each of the two sections of the module, there is a connector that allows you to combine the digital recording modules with a cable system into a single bottom braid. In this case, the part of the module housing forming the second section may be made of a polymer material. Polymethylsiloxane liquid was used as an easily compressible liquid. At least two orthogonally oriented geophones are located in the first section of the module, on the microcontroller board in the second section there is a two or three-axis accelerometer designed to determine the orientation of the module relative to the gravity vector.

The claimed technical solution allows you to apply the latest technology based on molecular electronics to increase sensitivity and reduce the level of intrinsic noise of previously known technical solutions. The resulting multifunctional seismic observation device is able to withstand static pressures of up to 50 atmospheres and function independently or as part of a bottom spit. The location of the electronic module inside the silicone fluid will reduce the strength requirements with respect to the external hydrostatic pressure for the electronics section, and will solve the problem of facilitating and reducing the cost of the device case, while maintaining all the functionality, since the pressure inside the case with the electronics will be practically the same as and external. In addition, since the liquid inside the hydrophone section is highly hydrophobic, this further protects the electronic components from leakage.

The invention is illustrated by drawings.

In FIG. 1 is a diagram of an example embodiment of the invention, where: 1 - a two-section housing of a digital recording module, 2 - mutually perpendicular molecular-electronic geophones in a section at atmospheric pressure, 3 - a sensitive element of a molecular-electronic hydrophone, 4 - an easily compressible liquid filling the entire internal volume the second section, 5 - electronic power, amplification and frequency correction boards, ADC, microcontroller and network adapter, 6 - leak-through sealed connectors that allow power supply, take a digital signal from one or more (up to 400) digital recording modules connected to the circuit, 7 - sealed through contacts between sections.

FIG. 2 is a photograph of an example implementation with an open section for molecular electronic geophones and a section for electronic circuit boards and a molecular electronic hydrophone already filled with easily compressible liquid.

FIG. 3 is a photograph of test measurements of the technical parameters of a digital measuring module under pressure on a test bench.

FIG. 4 and FIG. 5 - photographs of field tests of digital recording modules in a natural reservoir.

FIG. 6 - spectral power density of the intrinsic noise used in the measuring module of the molecular-electronic hydrophone in dB relative to 1 μPa / √Hz (Blue - intrinsic noise, Red - sensor signals in the experiment).

FIG. 7 - spectral power density of the intrinsic noise used in the measuring module of molecular-electronic geophones in dB relative to 1 m / s ² / √Hz (Black - intrinsic noise, Red and blue - sensor signals in the experiment).

The digital recording module, designed to measure the vertical component of the seismic velocity field at the bottom of reservoirs, contains an elongated metal casing 1, which is composed of two functional sections. In the first section, filled with air, there is at least one molecular-electronic geophone 2, and in the second section, filled with an easily compressible liquid, there is a sensitive element of the molecular-electronic hydrophone 3, as well as electronic boards 5 for power, amplification and frequency correction, a board ADC and microcontroller board. In the particular case of the implementation of the module, the part of the housing forming the second section is made of a polymer material, such as plastic or polycarbonate, and the integrity of the said section under the action of external hydrostatic pressure is ensured by elastic forces arising from a change in the volume of the easily compressible liquid filling the section 4. The sections are isolated from each other a spacer containing, the membrane of the molecular-electronic hydrophone, open to the external environment. The second membrane of the hydrophone faces one of the sections. In addition, for the electrical connection of the two sections, sealed wire contacts are formed between them, capable of withstanding the static pressure sufficient for the functioning and operation of the hydrophone. The section containing the sensitive element of the molecular-electronic hydrophone is completely filled with easily compressible liquid 4 with good hydrophobic properties, similar to the solution described in RU 2696060 C1, while in this section all electronic boards are fixed and connected to the terminal output section 6 and through-pass contacts 5 digital recording modules. The section is hermetically sealed so that no air bubbles remain in the liquid. At the same time, in the second section of the digital recording module, there is a mutually perpendicular pair of molecular-electronic geophones connected by means of electrical hermetic feed-through contacts to an electronic circuit board located in the section with easily compressible liquid, and the pair is fixed so that the electronic circuit boards of the liquid section are oriented along one from the axes of geophones. On the electronic board there is a three-component MEMS type accelerometer, two axes of which are obtained coaxially with the geophones of the measuring module, the third axis will determine the angle with respect to the vertical at which the measuring module lies at the bottom. The section with geophones also contains a sealed output connector that allows you to receive a signal from subsequent digital modules, if connected to the bottom of the scythe and supply them with power. Feed-through connections can be realized by means of industrial solder-in insulators with glazed lead-through terminals.

A diagram of an example implementation of a technical solution is shown in FIG. 1. In accordance with the indicated scheme and description of the invention, an example of implementation of FIG. 2 and FIG. 3. PMS-5 (polymethylsiloxane liquid), which has excellent hydrophobic properties and a volume compressibility coefficient of about two times higher than that of water, was selected as the volume-filling section with liquid plates.

In accordance with the description of the invention in FIG. 1 marked: 1 - two-section housing of the digital module, 2 - mutually perpendicular molecular-electronic geophones in the section at atmospheric pressure, 3 - molecular-electronic hydrophone, 4 - silicone fluid based on PMS-5, filling the entire internal volume of the second section, 5 electronic boards for power supply, amplification and frequency correction, ADC, microcontroller and network adapter, 6 - pass-through sealed connectors that allow power supply, take a digital signal from one or more (up to 400) digital recording modules connected to the circuit, 7 - sealed through contacts between sections.

For the collected implementation examples, the necessary set of test tests was carried out, the measuring parameters of the module are set to the following values:

Molecular-electronic geophones:

- working frequency band: 1 ÷ 300 Hz;

- sensitivity of the geophone: 250 V / m / s;

- intrinsic noise - 100 nm / s in the band 1-300 Hz

Molecular electronic hydrophone:

- working frequency band: 1 ÷ 500 Hz;

- hydrophone sensitivity: 300 μV / Pa;

- working hydrostatic pressure: up to 50 atm;

- spectral density of intrinsic noise at a frequency of 10 Hz with respect to 1 μPa ≤ 48 dB.

Digital system:

- ADC capacity: 24 bits;

- effective dynamic range of the ADC: ≥123 dB at f reg = 1 kHz and coefficient. gain 1;

- 100 Mbps local area network with data relaying - up to 400 modules per streamer.

The field tests of the measuring module demonstrated high sensitivity parameters and extremely low values of the intrinsic noise of FIG. 6 and FIG. 7.

Sources of information

1. A.S. Shabalina, D.L. Zaitsev, E.V. Egorov, I.V. Egorov A.N. Antonov, A.S. Bugaev, V.M. Agafonov, V.G. Krishtop. "Molecular-electronic converters in modern measuring instruments." Advances in modern radio electronics. No. 9, 2014, pp. 33-42.

2. Egorov, I.V .; Shabalina, A.S .; Agafonov, V.M. Design and self-noise ofMET closed-loop seismic accelerometers. IEEE Sens. J. 2017, 17, 2008-2014.

3. Avdyukhina S.Yu., Agafonov B.M., Egorov E.B., Zaitsev D.L., Ryzhkov M.A. “DEVICE AND PRINCIPLE OF ACTION OF MOLECULAR ELECTRON HYDROPHONE”, Applied technologies of hydroacoustics and hydrophysics, Proceedings of the XIV All-Russian Conference. 2018.S. 621-624.

4. Zaitsev, D.L., Avdyukhina, S.Y., Ryzhkov, M.A., Evseev, I., Egorov, E.V., and Agafonov, V. M .: Frequency response and self-noise of the MET hydrophone, J. Sens. Sens. Syst, 7, 443-452, https://doi.org/10.5194/jsss-7-443-2018, 2018.

5. V.M. Agafonov, I.V. Egorov, A.S.Shabalina "Principles of operation and technical characteristics of a small-sized molecular-electronic seismic sensor with negative feedback" Seismic instruments. 2013.V. 49, No. 1, p. 5-18.

6. Dmitry Zaitsev, Egor Egorov, Maxim Ryzhkov, Grigory Velichko, Prof. Vladimir Gulenko “LOW-FREQUENCY, LOW-NOISE MOLECULAR-ELECTRONIC HYDROPHONE FOR OFFSHORE AND TRANZIT ZONE SEISMIC EXPLORATION”, 19th INTERNATIONAL MULTIDISCIPLINARY SCIENTIFIC GEOCONFERENCE & EXPO SGEM 2019, June 28 - July 7. June Conference pp 961-968.

Claims (8)

1. A digital recording module designed to measure the vertical component of the seismic velocity field at the bottom of water bodies, as well as to record the acoustic wave pressure field in the medium, characterized in that it contains a housing consisting of two sections, and in the first section filled with air, at least one molecular-electronic geophone, and in the second section, filled with an easily compressible liquid, there is a sensitive element of the molecular-electronic hydrophone, as well as electronic power, amplification and frequency correction boards, an ADC board and a microcontroller board, while the sections are isolated from each other a spacer containing sealed wire contacts and a membrane open to the external environment. 2. The module according to claim 1, characterized in that it contains a battery that provides independent power supply to the module. 3. The module according to claim 1, characterized in that it contains an internal data storage device in the form of an internal memory for autonomous recording of seismic-acoustic data. 4. The module according to claim 1, characterized in that it contains a network adapter that allows, if necessary, to transmit data recorded by the sensor to external devices. 5. The module according to claim 1, characterized in that in each of the two sections there is a connector that allows you to combine the digital recording modules with a cable system into a single bottom braid. 6. The module according to claim 1, characterized in that the part of the housing forming the second section is made of polymer material. 7. The module according to claim 1, characterized in that polymethylsiloxane liquid is used as an easily compressible liquid. 8. The module according to claim 1, characterized in that at least two orthogonally oriented geophones are located in the first section, on the microcontroller board in the second section there is a two or three-axis accelerometer designed to determine the orientation of the module relative to the gravity vector.

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