AU2020104461A4

AU2020104461A4 - Device for high-precision measurement of wavelets from plasma source in shallow water

Info

Publication number: AU2020104461A4
Application number: AU2020104461A
Authority: AU
Inventors: Qianqian Li; Hongwei Liu; Huaishan LIU; Boran LV; Lei XING; Jin Zhang
Original assignee: Ocean University of China
Current assignee: Ocean University of China
Priority date: 2020-09-02
Filing date: 2020-09-02
Publication date: 2021-10-14
Anticipated expiration: 2028-09-02

Abstract

Disclosed is a device for the high-precision measurement of wavelets from a plasma seismic source in shallow water conditions, including two submarine cables and a vertical cable connected to a digital package, and a floating ball and an underwater compass; two submarine cables are respectively arranged along an x direction and a y direction, a top end of the vertical cable is connected to the floating ball, a bottom end thereof is connected to the digital package, the vertical cable is arranged along a z direction and has a length less than water depth; and the underwater compass is fixed on the vertical cable; the submarine cables are provided with a plurality of sensor groups at equal intervals; each sensor group includes a vibrating sensor and a pressure sensor; the vertical cable is provided with a plurality of sensor groups at equal intervals; and each sensor group consists of two pressure sensors in parallel. In this present disclosure, the submarine cables and vertical cable are used to achieve three-dimensional observation of wavelets from a plasma seismic source in shallow water conditions, thus improving the measurement accuracy of seismic source wavelets in shallow water conditions, and monitoring a variation law of seismic source wavelets in both horizontal and vertical directions. Moreover, vertical cables and submarine cables can greatly reduce noise disturbance relative to horizontal streamers. REPRESENTATIVE DRAWING: FIG. 1 Seismic source stimulation Sea surface 4 5 / 3 FIG. 1 303 304 307 )302 308-. ?305 309, -306 310- UT [ T311 313 -- 312 301 FIG. 2 1 /12

Description

Seismic source stimulation

Sea surface

4 5

3 /

FIG. 1

303 304 307 )302 308-. ?305 309, -306 310- [ UT T311

313 -- 312 301

FIG. 2

1 /12

DEVICE FOR HIGH-PRECISION MEASUREMENT OF WAVELETS FROM PLASMA SOURCE IN SHALLOW WATER FIELD

The present invention relates to a stereoscopic seismic wavelet measurement

device in marine seismic exploration, and in particular to a device for the

high-precision measurement of wavelets from a plasma source in shallow water

conditions.

BACKGROUND

The basic working principle of a plasma seismic source is to form strong

pressure pulse by high-energy plasma channels generated by pulse discharge in

water. Plasma seismic source has the advantages of high basic frequency of

wavelet, wide frequency bandwidth, fast charging and discharging, high

resolution ratio, strong reflected energy and good continuity of phase axis.

The far-field wavelet of plasma seismic source is not only an important

index to measure the performance of seismic source, but also an important input

data in seismic data processing. The far-field wavelet of plasma seismic source

can obtain the signal property relatively simply, and it is easy to be visualized

and understood, which is an important standard to measure the performance of

seismic source.

Under shallow water conditions, complex multiple waves, guided waves,

tides, surges and other special interference waves and water structures seriously

affect the stability of plasma source wavelet. Because the conventional

multi-channel horizontal cables are closer to the sea level, the and observation

system is in a dynamic process, the accuracy of the data obtained is low, the

resolution rate can only meet the demands for medium-deep or shallow

engineering seismic exploration, which cannot meet the requirements of

I high-precision seismic exploration; the conventional shallow earthquake and shallow seismic profile and other methods have the disadvantages of narrow frequency band and poor anti-interference ability, and cannot obtain the accurate far-field wavelet of plasma seismic source.

Therefore, in view of the limitations of the prior art and the particularity of

shallow water conditions, there is no device for measuring wavelets of plasma

seismic source in shallow water conditions currently, and it is necessary to design

such a device.

SUMMARY

The objective of the present disclosure is to provide a device for the

high-precision measurement of wavelets from a plasma seismic source in shallow

water conditions to overcome the shortcomings of the prior art.

A device for the high-precision measurement of wavelets from a plasma seismic

source in shallow water conditions, including two submarine cables and a vertical

cable connected to a digital package, and a floating ball and an underwater compass;

where the digital package is located on the seabed, two submarine cables are

respectively arranged along an x direction and a y direction, a top end of the vertical

cable is connected to the floating ball, and a bottom end is connected to the digital

package, the vertical cable is arranged along a z direction and has a length less than

water depth, and the underwater compass is fixed on the vertical cable;

the above submarine cables are provided with a plurality of sensor groups at

equal intervals, where each sensor group includes a vibrating sensor and a pressure

sensor which independently record waveforms and respectively transmit to the digital

package for storage, and the channel interval among sensor groups is 0.5 m, and the

number of channels is 8 to 16; the above vertical cable is provided with a plurality of

sensor groups at equal intervals, and each sensor group consists of two pressure

sensors in parallel, and the channel interval is 0.5 m; the number of channels of a sound pressure sensor is 8 to 16; the pressure and vibrating sensors are used to measure scalar and vector information of the seabed location respectively; the above digital package includes a base and a hollow spherical shell above the base, the shell is provided with a pressure sensor, a temperature sensor and a GPS, where the GPS is used for time service of the whole device, and the pressure sensor and the temperature sensor are used for continuously recording the depth and temperature parameters of the digital package for all time intervals; the shell is provided with a battery chamber at a lower portion of an inner cavity thereof, and is provided with a high-capacity lithium battery therein, and is provided with four layers of digital boards on an upper portion thereof; where, one-layer digital board includes a main control board, a GPS and tilt angle data acquisition board, a temperature and pressure data acquisition board, a data cache memory board A and a data cache memory board B; the other three layers of digital boards are respectively used for acquiring data of cables in x, y and z directions; each layer includes a seismic data acquisition board and an analog-to-digital conversion board whose number is equal to the number of cables in the direction; the above GPS and tilt angle data acquisition board is connected to and the GPS for acquiring data in the GPS and transmitting the acquired data to the data cache memory board A for storage; the temperature and pressure data acquisition board is used for acquiring the data in the temperature sensor and pressure sensor, and outputting the data to the data buffer storage board A for storage; the data cache memory board B is used to store data acquired by the submarine cables and the vertical cable.

The submarine cable includes an outer protective casing, a vibrating sensor, a pressure sensor and wires; the pressure sensor and vibrating sensor are both located in the outer protective casing, and are connected to the digital package via multiple groups of wires located in the outer protective casing; and a polyurethane solid material is filled between the inside of the outer protective casing and each of the pressure sensor and vibrating sensor. The outer protective casing of the submarine cable is made of a high-strength polyamide material, and Kevlar fibers are mixed in the polyamide material.

The vertical cable includes an outer protective casing, a vibrating sensor, a

pressure sensor and wire; the pressure sensor and vibrating sensor are both located in

the outer protective casing, and are connected to the digital package via multiple

groups of wires located in the outer protective casing; and a polyurethane solid

material is filled between the inside of the outer protective casing and a sound

pressure sensor. The outer protective casing of the vertical cable is made of a

high-strength polyamide material, and Kevlar fibers are mixed in the polyamide

material.

An end connector is arranged on an end of the vertical cables or the submarine

cable connected to the digital package; the end connector is provided with a protective

casing made of high-strength titanium alloy; the diameter of the protective casing

trends a step-wise increase from a tail end of the vertical cable towards a direction of

the digital package; the digital package is provided with a 19-pin watertight joint at a

top portion thereof, and connected to an end connector of the vertical cable by the

19-pin watertight joint; and the submarine cables are connected to the digital package

by the 19-pin watertight joint located on a side of the digital package.

ARM9 is used as a master controller in the main control board of the digital

package to control the operation of the whole digital package; a CS5372/5376

component is used to constitute a 32-bit analog-to-digital converter; ACTEL,

AGL250V5, FPGA are used for address latching, gating, data serial-to-parallel format

conversion, counting, frequency division and logic control; FIFO buffer and flash

memory electronic disk are used to ensure the accuracy and validity of recorded data.

The battery chamber is provided with a lithium battery and a circuit unit. The lithium battery is charged through a 19-pin watertight connector at the top portion of the digital package, which is responsible for supplying power to each component of the whole device; and the circuit unit is responsible for converting battery voltage into various power sources required by the acquisition system, including digital system power source, analog system power source, A/D converter high-precision reference voltage, etc.

In this disclosure, submarine cables and vertical cables are used to measure

wavelets from a plasma seismic source in shallow water conditions. Compared with

the conventional measuring device, the disclosure is applicable to such a specific

environment of shallow water and is a device for measuring high-frequency wavelets

from a plasma seismic source. Moreover, the present invention has the following

significant advantages:

a. the disclosure achieves three-dimensional observation by 0.5 m channel

arrangement, and increases the sampling point density compared with the

conventional seismic acquisition of 6.25 m channel spacing or 12.5 m channel spacing,

which improves the measurement accuracy of the seismic source wavelet in shallow

water conditions, and achieves analog-to-digital conversion board;

b. the combined measurement of submarine cables and vertical cables is used to

monitor a variation law of iso-source wavelet in both horizontal and vertical

directions;

c. relative to horizontal streamers, vertical cables and submarine cables are put to

the seabed, thus are far from the surface of the sea, free from the effects of wave and

surge noise, and are in a stationary state during data collection, thereby greatly

reducing noise interference;

d. an underwater compass is fixed on the vertical cable, which can record the

posture of the vertical cable and reduce the measurement error;

e. a temperature and pressure sensor is provided, which can acquire temperature

and pressure information, thus accurately inverting the evolution process of the seismic source wavelet; f GPS is provided for clock correction after putting and recovering the device, thus eliminating the influence of clock drift; g. Kevlar fibers are provided in the outer protective casing of the acquisition cable to increase the tensile strength having a tensile resistance of 1 ton above; h. the use of a stepped end connector can not only ensure the stability of the joint connection, but also can bend in a certain range, convenient for collection and release; i. a CS5372/5376 component is used to constitute a 32-bit analog-to-digital converter; the dynamic range is up to 128 dB, time sampling rate may be up to 1/64 ms, and multiple sampling rates can be selected: 1/64 ms, 1/32 ms, 1/16 ms, 1/8 ms,

1/4 ms, 1/2 ms.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing an overall structure of the present

disclosure.

FIG. 2 is a schematic diagram showing an inner structure of a digital package of

the present disclosure.

FIG. 3 is an exploded view showing a watertight joint of the digital package of

the present disclosure.

FIG. 4 is a front view of the watertight joint.

FIG. 5 is a front view of the watertight joint.

FIG. 6 is a perspective view of the watertight joint.

FIG. 7 is an exploded view showing end connectors of vertical and submarine

cables of the prevent disclosure (without a protective casing).

FIG. 8 is a cross-sectional view of the end connector.

FIG. 9 is a perspective view of the end connector.

FIG. 10 is an assembly drawing of the watertight joint of the present disclosure.

1 denotes submarine cable, 2 denotes vertical cable, 3 denotes digital package, 4

denotes floating ball, 5 denotes underwater compass, 301 denotes digital package

watertight joint, 302 denotes pressure sensor, 303 denotes GPS, 304 denotes

temperature sensor, 305 denotes main control board, 306 denotes GPS and tilt angle

data acquisition board, 307 denotes temperature and pressure acquisition board, A308

denotes data cache memory board, B309 denotes data cache memory board, 310

denotes seismic data acquisition board, 311 denotes analog-to-digital conversion

board, 312 denotes battery chamber, and 313 denotes a base.

DETAILED DESCRIPTION

As shown in FIG. 1, the present disclosure includes two submarine cables 1, a vertical

cable 2, a digital package 3, a floating ball 4 and an underwater compass 5. The digital

package 3 is located on the seabed, two submarine cables 1 are respectively arranged

along an x direction and a y direction, a top end of the vertical cable 2 is connected to

the floating ball 4, and a bottom end thereof is connected to the digital package 3, the

vertical cable 2 is arranged along a z direction and has a length less than water depth,

and the underwater compass 5 is fixed on the vertical cable 2; and the floating ball 4

renders the vertical cable 2 to keep vertical. The base has a higher weight to make the

whole device fixed to the seabed. The three cables are perpendicular to each other to

constitute a stereoscopic observation way. The above submarine cable 1 is provided

with a plurality of vibrating sensors and pressure sensors at equal intervals; the same

pressure sensors and vibrating sensors are arranged at the same position of the

submarine cable 1 and are respectively used for measuring scalar and vector information about the position of the seabed; and the vertical cable 2 is provided with a plurality of pressure sensors at equal intervals; as shown in FIG. 2, the digital package 3 of the present disclosure includes a base 313 and a hollow spherical shell 301 above the base 313; the shell is provided with a pressure sensor 302, a temperature sensor 304 and a GPS 303; the shell is provided with a battery chamber 312 at a lower portion of an inner cavity thereof, and is provided with a high-capacity lithium battery therein, and is provided with four layers of digital boards on an upper portion thereof; where, one-layer digital board includes a main control board 305, a GPS and tilt angle data acquisition board 306, a temperature and pressure data acquisition board 307, a data cache memory board A308 and a data cache memory board B309; in addition, the other three layers of digital boards are respectively used for acquiring data of cables in x, y and z directions; each layer includes a seismic data acquisition board 310 and an analog-to-digital conversion boards 311 whose number is equal to the number of cables in the direction; the GPS and tilt angle data acquisition board 306 is connected with the GPS 303, used for acquiring data in the GPS 303 and transmitting the acquired data to the data cache memory board A308 for storage; the temperature and pressure data acquisition board 307 is respectively used to acquire data in the temperature sensor 304 and pressure sensor 302, and to output data to the data cache memory board A308 for storage; and the data cache memory board B309 is used to store the data acquired by the submarine cable 1 and the vertical cable 2.

ARM9 is used as a master controller in the main control board 305 of the digital package 3 to control the operation of the whole digital package 3; a CS5372/5376 component is used to constitute a 32-bit analog-to-digital converter; ACTEL, AGL250V5, FPGA are used for address latching, gating, data serial-to-parallel format conversion, counting, frequency division and logic control; an FIFO buffer and a flash memory electronic disk are used to ensure the accuracy and validity of recorded data.

The submarine cable 1 includes an outer protective casing, a vibrating sensor, a pressure sensor and wires; the pressure sensor and vibrating sensor are both located in the outer protective casing, and are connected to the digital package 3 via multiple groups of wires located in the outer protective casing; and a polyurethane solid material is filled between the inside of the outer protective casing and each of the pressure sensor and vibrating sensor. The outer protective casing of the submarine cable 1 is made of a high-strength polyamide material, and Kevlar fibers are mixed in the polyamide material. In the submarine cable 1, the pressure sensor and the vibrating sensor are combined in parallel, the channel pitch is 0.5 m, and the number of channel s is 8 to 16.

The vertical cable 2 includes an outer protective casing, a vibrating sensor, a pressure sensor and wires; the pressure sensor is located in the outer protective casing, and is connected to the digital package 3 via multiple groups of wires located in the outer protective casing; and a polyurethane solid material is filled between the inside of the outer protective casing and a sound pressure sensor. The outer protective casing of the vertical cable 2 is made of a high-strength polyamide material, and Kevlar fibers are mixed in the polyamide material. In the vertical cable 2, two pressure sensors are combined in parallel for each channel, the channel spacing is 0.5 m, and the number of channels is 8 to 16.

As shown in FIGS. 3-10, an end connector is arranged on an end of the vertical cables 2 or the submarine cable 1 connected to the digital package 3; the end connector is provided with a protective casing made of high-strength titanium alloy; the diameter of the protective casing trends a step-wise increase from a tail end of the vertical cable 2 towards a direction of the digital package 3; the digital package is provided with a 19-pin watertight joint at a top portion thereof, and connected to an end connector of the vertical cable 2 by the 19-pin watertight joint; and the submarine cables 1 are connected to the digital package 3 by the 19-pin watertight joint located on a side of the digital package 3. The watertight joints are divided into male and female parts; the watertight joints on the digital package 3 are female parts, the watertight joints on the cable are male parts; the watertight joints are formed by a grading nested combination of multiple components; the inner 19-pin joints keep still, and are connected and fixed by external rotatable screws; a protective casing made of high-strength titanium alloy is arranged at the watertight joint and at a connecting portion connected with cables; the diameter of the protective casing trends a step-wise increase from the cable towards the watertight joint; there is a certain clearance among each protective casing, so that the protective casing may bend within a certain scope.

The battery chamber 312 is provided with a lithium battery and a circuit unit. The lithium battery is charged through a 19-pin watertight connector located at the top portion of the digital package 3, which is responsible for supplying power to each component of the whole device; and the circuit unit is responsible for converting battery voltage into various power sources required by the acquisition system, including digital system power source, analog system power source, A/D converter high-precision reference voltage, etc.

During the use procedure of the present disclosure, the submarine cables 1 and the vertical cable 2 are firstly tested, the watertight joints of the digital package and the cable are connected and sealed, interfaces of each part are carefully inspected to ensure free of looseness; the voltage and electric quantity of the battery are tested, and then components of the complete device are assembled. GPS positioning is performed for time service to the device, so that the device enters the acquisition state. After a working ship reaches the preset point location, the floating ball and vertical cable are slowly put to the water, then the digital package is released, then two submarine cables are pulled down slowly, ends of the submarine cables are connected by a Kevlar rope, after the digital package is sunk into the sea, and then a submarine cable is towed to a pre-designed designated position by a small boat, then the rope is pulled to place the submarine cable slowly to the seabed, and finally, another submarine cable is placed at the designated position in the same manner.

After the cable is placed, a plasma seismic source is excited to perform data acquisition, and at the end of the operation, the complete set of device is recovered and data is read. During the construction, the seismic source wavelet signals received by the device are converted from analog signals to digital signals and transmitted to the storage and recording unit in the digital package for acquisition and recording. Meanwhile, the temperature sensor and pressure sensor above the digital package record the environmental information of the device, and the underwater compass records the attitude information of the vertical cable.

Claims

WHAT IS CLAIMED IS:

1. A device for the high-precision measurement of wavelets from a plasma

seismic source in shallow water conditions comprising: two submarine cables (1)

and a vertical cable (2) connected to a digital package (3), and a floating ball (4)

and an underwater compass (5); wherein the digital package (3) is located on the

seabed, two submarine cables (1) are respectively arranged along an x direction

and a y direction, a top end of the vertical cable (2) is connected to the floating

ball (4), and a bottom end of the vertical cable (2) is connected to the digital

package (3), the vertical cable (2) is arranged along a z direction and has a length

less than water depth, and the underwater compass (5) is fixed on the vertical

cable (2);

the above submarine cables (1) are provided with a plurality of sensor

groups at equal intervals, wherein each sensor group comprises a vibrating sensor

and a pressure sensor which independently record waveforms and respectively

transmit to the digital package for storage, and the channel interval among sensor

groups is 0.5 m, and the number of channels is 8 to 16; the above vertical cable (2)

is provided with a plurality of sensor groups at equal intervals, and each sensor

group consists of two pressure sensors in parallel, and the channel interval is 0.5

m; the number of channels of a sound pressure sensor is 8 to 16; the pressure and

vibrating sensors are used to measure scalar and vector information of the seabed

location respectively;

the above digital package (3) comprises a base (313) and a hollow spherical

shell (301) above the base (313), the shell (301) is provided with a pressure

sensor (302), a temperature sensor (304) and a GPS (303), wherein the GPS (303)

is used for time service of the whole device, and the pressure sensor (302) and

the temperature sensor (304) are used for continuously recording the depth and

temperature parameters of the digital package (3) for all time intervals;

a battery chamber (312) is provided at a lower portion of an inner cavity of

the shell (301), and a high-capacity lithium battery is provided in the shell (301), and four layers of digital boards are provided on an upper portion of the shell

(301); wherein, one-layer digital board comprises a main control board (305), a

GPS and tilt angle data acquisition board (306), a temperature and pressure data

acquisition board (307), a data cache memory board A (308) and a data cache

memory board B (309); the other three layers of digital boards are respectively

used for acquiring data of cables in x, y and z directions; each layer comprises a

seismic data acquisition board (310) and analog-to-digital conversion boards

(311) whose number is equal to the number of cables in the direction;

the above GPS and tilt angle data acquisition board (306) is connected with

the GPS (303) for acquiring data in the GPS (303) and transmitting the acquired

data to the data cache memory board A (308) for storage;

the temperature and pressure data acquisition board (307) is used for

acquiring data in the temperature sensor (304) and the pressure sensor (302), and

outputting the data to the data cache memory board A (308) for storage;

the data cache memory board B (309) is used to store data acquired by the

submarine cables (1) and the vertical cable (2).

2. The device for the high-precision measurement of wavelets from a plasma

seismic source in shallow water conditions of claim 1, wherein the submarine

cables (1) further comprise an outer protective casing, a vibrating sensor, a

pressure sensor and wires; the pressure sensor and vibrating sensor are both

located in the outer protective casing, and are connected to the digital package (3)

via multiple groups of wires located in the outer protective casing; and a

polyurethane solid material is filled between the inside of the outer protective

casing and each of the pressure sensor and vibrating sensor.

3. The device for the high-precision measurement of wavelets from a plasma

seismic source in shallow water conditions of claim 1, wherein the vertical cable

(2) comprises an outer protective casing, a pressure sensor and wires; the

pressure sensor is located in the outer protective casing, and is connected to the digital package (3) by multiple groups of wires located in the outer protective casing, and a polyurethane solid material is filled between the inside of the outer protective casing and a sound pressure sensor.

4. The device for the high-precision measurement of wavelets from a plasma

seismic source in shallow water conditions of claim 1, wherein an end

connector is arranged on an end of the vertical cables (2) or the submarine cable

(1) connected to the digital package (3); the end connector is provided with a

protective casing made of high-strength titanium alloy; the diameter of the

protective casing trends a step-wise increase from a tail end of the vertical cable

(2) towards a direction of the digital package (3); a 19-pin watertight joint is

provided at a top portion of the digital package, and the digital package

connected to the end connector of the vertical cable (2) by the 19-pin watertight

joint; and the submarine cables (1) are connected to the digital package (3) by the

19-pin watertight joint located on a side of the digital package (3) respectively.