CN111323810A - Marine seismic detection system with seismic source below towing cable and method thereof - Google Patents

Marine seismic detection system with seismic source below towing cable and method thereof Download PDF

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CN111323810A
CN111323810A CN202010181638.5A CN202010181638A CN111323810A CN 111323810 A CN111323810 A CN 111323810A CN 202010181638 A CN202010181638 A CN 202010181638A CN 111323810 A CN111323810 A CN 111323810A
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seismic
depth
seismic source
towing
streamers
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CN111323810B (en
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沈洪垒
陶春辉
王汉闯
周建平
柳云龙
丘磊
顾春华
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Second Institute of Oceanography MNR
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
    • G01V1/16—Receiving elements for seismic signals; Arrangements or adaptations of receiving elements
    • G01V1/18—Receiving elements, e.g. seismometer, geophone or torque detectors, for localised single point measurements
    • G01V1/186—Hydrophones
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
    • G01V1/02—Generating seismic energy
    • G01V1/04—Details
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
    • G01V1/02—Generating seismic energy
    • G01V1/157—Generating seismic energy using spark discharges; using exploding wires
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
    • G01V1/02—Generating seismic energy
    • G01V1/159—Generating seismic energy using piezoelectric or magnetostrictive driving means
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
    • G01V1/16—Receiving elements for seismic signals; Arrangements or adaptations of receiving elements
    • G01V1/20—Arrangements of receiving elements, e.g. geophone pattern
    • G01V1/201—Constructional details of seismic cables, e.g. streamers
    • G01V1/208—Constructional details of seismic cables, e.g. streamers having a continuous structure
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A90/00—Technologies having an indirect contribution to adaptation to climate change
    • Y02A90/30—Assessment of water resources

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Abstract

The invention discloses a marine seismic detection system with a seismic source below a towing cable and a method thereof, belonging to the field of marine seismic exploration. The system comprises a mother ship, a seismic source, a photoelectric composite cable and a free-standing combined towing device; the mother ship is connected with a seismic source through a photoelectric composite cable; the independent combined towing device is fixed on the photoelectric composite cable through a hoop; the independent combined towing device comprises a power supply and acquisition unit, a plurality of towing cables and a resistance device; the method comprises the steps of firstly laying a seismic source according to an exploration target, then fixing the depth of a plurality of towing cables by adjusting the positions of hoops on the photoelectric composite cables, and finally adjusting the distance between the hoops and a power supply and acquisition unit to enable the seismic source to be located under the middle positions of the plurality of towing cables. The invention can record the near (zero) offset which is crucial to the imaging of the seabed shallow structure on one hand, and can acquire the shallow high-resolution seismic data which are not influenced by ghost waves on the other hand, thereby effectively improving the imaging effect of the seabed shallow structure.

Description

Marine seismic detection system with seismic source below towing cable and method thereof
Technical Field
The invention belongs to the field of marine seismic exploration, and particularly relates to a marine seismic detection system with a seismic source below a towing cable and a method thereof.
Background
In the existing marine multi-channel seismic detection system, an air gun is generally used as a seismic source, and a streamer is positioned at a certain distance behind the seismic source. The seismic sources are usually placed in the depth range of 5-20m underwater, and can adopt a single-depth or multi-depth combined mode, and the streamers are generally placed between 5-50m underwater and are in a horizontal or inclined attitude. The acquisition mode can ensure that the middle-deep part reflected signal is obtained, but the loss of near (zero) offset data is caused, and the imaging precision of the seabed shallow structure is reduced. Meanwhile, due to the existence of a seawater-air strong reflection interface, seismic source ghost waves and hydrophone end ghost waves are introduced into the seismic record, so that a notch effect in a frequency domain is caused, and the effective frequency bandwidth and the stratum resolution of seismic data are reduced.
The seismic data acquired by the multi-channel seismic acquisition system need to perform dynamic correction on the common reflection point gather before stacking, and the dynamic correction values of different offset data can be represented as follows:
Figure BDA0002412765630000011
wherein, t0Is the self-excited self-receiving time (zero offset), x is the offset, vNMOThe velocity is dynamically corrected.
The motion correction process causes different degrees of motion-corrected stretching of the data, usually expressed in terms of frequency distortion:
Figure BDA0002412765630000012
where f is the dominant frequency and Δ f is the frequency distortion.
The dynamic correction stretching is increased along with the increase of water depth and the increase of offset distance, and when the common reflection point gather is superposed, the gather which is stretched too much needs to be cut off so as to ensure the formation resolution. The conventional acquisition mode lacks small offset data, so that seabed shallow data, particularly effective superposed tracks in a shallow water area are too few, and the subsequent imaging effect is influenced.
In addition, the conventional air gun seismic source and towing cable are placed in shallow water, seismic source wavelets excited by an air gun form seismic source ghost waves following head waves after being reflected by the sea surface, the head waves and the ghost waves are reflected by an underground reflection layer, then upwards transmitted to the towing cable and recorded by the hydrophone, and a wave field is reflected again by the sea surface after continuously upwards transmitted and then reaches the towing cable to form ghost waves at the hydrophone end. The ghost waves complicate the original simple source wavelet, and cause notch in the frequency domain, which seriously affects the wavelet spectrum integrity, thereby reducing the effective frequency bandwidth of the seismic data. Therefore, by reasonably designing the marine seismic acquisition system, the effective stacking channel number of the shallow water area is increased, and the acquisition of shallow high-resolution seismic data which are not influenced by ghost waves has important significance for imaging of the seabed shallow structure.
Disclosure of Invention
The invention aims to overcome the defects of the prior art, and provides a marine seismic detection system with a seismic source positioned below a towing cable and a method thereof in order to record a near (zero) offset which is crucial to imaging of a seabed shallow structure, acquire shallow high-resolution seismic data which are not influenced by ghost waves and improve the imaging effect of the seabed shallow structure.
The technical scheme of the invention is as follows:
a marine seismic exploration system with a seismic source located below a streamer comprises a mother ship, the seismic source, a photoelectric composite cable and a freestanding combined streamer device; the mother ship is connected with a seismic source through a photoelectric composite cable; the independent combined towing device is fixed on the photoelectric composite cable through a hoop; the independent combined streamer device is positioned above the seismic source and comprises a power supply and acquisition unit, a plurality of streamers and a resistance device; one end of the power supply and acquisition unit is connected with the hoop through a distance adjustable device, the other end of the power supply and acquisition unit is connected with the plurality of towing cables, the tail parts of the plurality of towing cables are connected with resistance devices assisting in straightening the towing cables, and the depth of the plurality of towing cables in the ocean can be adjusted by moving the position of the hoop on the photoelectric composite cable.
Preferably, the independent combined streamer device further comprises an auxiliary floating ball, and the auxiliary floating ball is arranged between the power supply and acquisition unit and the plurality of streamers.
Preferably, the seismic source is located directly below a mid-position of the plurality of streamers.
Preferably, a plurality of hydrophones are uniformly arranged on the plurality of streamers, and each hydrophone is connected with the power supply and acquisition unit through a data line.
Preferably, the plurality of streamers assume a horizontal attitude.
Preferably, the time of the double-stroke earthquake from the bottom of the sea to the bottom of the exploration target is ≧ (h-d)2) When/c, the seismic source is sunk to a position close to the sea bottom, and the depth of a plurality of towing cables is adjusted
Figure BDA0002412765630000021
Conversely, adjusting the depth of the multi-channel streamer
Figure BDA0002412765630000031
Where h is the depth of water, d2Is the depth difference between the seismic source and the streamer, and c is the velocity of sound in the water.
Preferably, the arrangement of the seismic sources is such that
Figure BDA0002412765630000032
Where Δ textThe duration of the seismic wavelet, d3The depth of the seismic source from the seafloor.
Preferably, the seismic source is a transducer or an electric spark seismic source.
The invention also discloses a marine seismic exploration method of the system, which comprises the following steps:
1) laying a seismic source and a plurality of towing cables according to an exploration target:
first determining that the seismic source depth satisfies
Figure BDA0002412765630000033
Where Δ textThe duration of the seismic wavelet, d2Depth difference between seismic source and multi-channel towing cable, d3The depth of the seismic source from the sea bottom, and c is the sound velocity in water;
when the exploration target moves from the seabed to the lower double-stroke earthquake, the walking time is not less than (h-d)2) When/c, the seismic source is sunk to a position close to the sea bottom, and the depth of a plurality of towing cables is adjusted
Figure BDA0002412765630000034
Conversely, adjusting the depth of the multi-channel streamer
Figure BDA0002412765630000035
Wherein h is water depth; the depths of the plurality of towing cables are fixed by adjusting the position of the hoop on the photoelectric composite cable; finally, adjusting the distance between the hoop and the power supply and acquisition unit to enable the seismic source to be positioned right below the middle position of the plurality of towing cables;
2) exciting a seismic source, transmitting seismic wavelets upwards to a plurality of towlines after the seismic wavelets are reflected at a reflection horizon where an exploration target area is located, and acquiring seismic signals by hydrophones on the plurality of towlines; the power supply and acquisition unit supplies power to the multiple towing cables and records the seismic data acquired by each hydrophone.
The invention has the beneficial effects that:
1) in the marine seismic detection system, a seismic source is positioned below a towing cable, the towing cable is powered by the power supply and acquisition unit and seismic data are recorded, meanwhile, the distance between the power supply and acquisition unit and the photoelectric composite cable can be adjusted, the seismic source can be positioned right below the middle position of the towing cable on the premise of not changing the depth of a plurality of towing cables and the depth of the seismic source, and the towing cable can record the near (zero) offset which is crucial to the imaging of a seabed shallow layer structure after the seismic source is excited;
2) the traditional seismic source and streamer cable are placed in shallow water, and seismic source ghost waves and hydrophone end ghost waves are easily introduced in seismic records due to the existence of a seawater-air strong reflection interface; according to the invention, as the seismic source is positioned below the towing cable, and the arrival time relation curves of different wave fields are researched when the seismic source and the towing cable are arranged at different water depths, the depths of the seismic source and the towing cable can be specifically distributed according to the detection target, and the method has strong adaptability to the detection targets at different depths below the seabed; the method can acquire shallow high-resolution seismic data which are not influenced by ghost waves, and further effectively improve the imaging effect of the seabed shallow structure;
3) compared with the traditional air gun as a seismic sound source, the invention adopts the energy converter or the electric spark source, has higher main frequency than the air gun, can realize deep sea operation, is more suitable for high-resolution exploration and is particularly suitable for seabed shallow structure detection;
4) the marine seismic exploration system has the advantages of low cost, simple structure and convenient operation of the exploration method.
Drawings
FIG. 1 shows the variation of the dynamic-correction stretch with different water depths (cut-off to 50%);
FIG. 2 shows the effect of seismic source ghost and hydrophone-end ghost on the head wave signal in time and frequency domains, taking impulse wavelet as an example; wherein, (a) the time domain, (b) the frequency domain;
FIG. 3 is a schematic diagram of a marine seismic acquisition system with seismic sources located below streamers in an embodiment of the invention;
FIG. 4 is a graph of the time of arrival (b) of different wavefields at the same depth difference (a) for source-multi-track streamers;
FIG. 5 is a graph of the time length of formation reflection without ghost influence as a function of seismic source depth;
FIG. 6 is a graph of the time of arrival (b) of different wavefields at different depth differences (a) for source-multi-channel streamers;
in the figure: 1 seismic source, 2 photoelectric composite cable,3 mother ship, 4 hoops, 5 power supply and acquisition units, 6 auxiliary floating balls, 7 multi-channel towing cables, 8 resistance devices and d1For multiple streamer depths, d2Is the depth difference between the seismic source and the multi-channel towing cable, d3The depth of the seismic source from the sea floor.
Detailed Description
The invention is further described with reference to the accompanying drawings.
Figure 1 shows the percentage of frequency distortion (cut-off to 50% distortion) for different offsets for different water depth conditions. By comparison, it can be found that the dynamic correction stretching increases with the increase of the water depth and the increase of the offset distance, and when the common reflection point gather is overlapped, the gather which is stretched too much needs to be cut off so as to ensure the formation resolution. The conventional acquisition mode lacks small offset data, so that seabed shallow data, particularly effective superposed tracks in a shallow water area are too few, and the subsequent imaging effect is influenced.
Fig. 2 shows the influence of the seismic source ghost and the hydrophone-end ghost on the head wave signal in the time domain and the frequency domain, taking the impulse wavelet as an example. By contrast, it can be found that the existence of ghost waves complicates the original simple source wavelet, and causes notch in the frequency domain, which seriously affects the wavelet frequency integrity, thereby reducing the effective frequency bandwidth of seismic data.
FIG. 3 is a schematic diagram of a marine seismic acquisition system of the present invention with seismic sources below streamers, including a parent vessel 3, a seismic source 1, a photoelectric composite cable 2, and a freestanding combined streamer device; the mother ship 3 is connected with the seismic source 1 through the photoelectric composite cable 2; the independent combined towing device is fixed on the photoelectric composite cable 2 through an anchor ear 4.
In one specific implementation of the invention, the seismic source part adopts a transducer or an electric spark seismic source which can work several kilometers under water, and the signal transmission and power supply are realized by connecting a mother ship through a photoelectric composite cable; the main frequency of the energy converter and the electric spark seismic source is higher than that of an air gun, so that the high-frequency deep sea wave. The acquisition part adopts a freestanding combined streamer in order to adjust the depth conveniently, and the freestanding combined streamer device is positioned above a seismic source and comprises a power supply and acquisition unit 5, a plurality of streamers 7 and a resistance device 8; one end of the power supply and acquisition unit 5 is connected with the hoop 4 through a distance adjustable device, the other end of the power supply and acquisition unit is connected with the plurality of towropes 7, and the power supply and acquisition unit 5 is used for supplying power to the plurality of towropes 7 and recording seismic data; the independent combined towrope device further comprises an auxiliary floating ball 6, wherein the auxiliary floating ball 6 is arranged between the power supply and acquisition unit 5 and the plurality of towropes 7 and is used for assisting in adjusting the depth of the front ends of the plurality of towropes 7; in actual operation, the multi-channel towline needs to ensure a horizontal posture, the multi-channel towline can realize equal buoyancy through material selection, the tail part of the multi-channel towline 7 is provided with a resistance device 8, the resistance device can be an umbrella-shaped device and can also be made of an equal buoyancy material, and the main purpose is to assist in straightening the multi-channel towline 7; a plurality of hydrophones are uniformly arranged on the multi-channel streamer 7, each hydrophone is connected with the power supply and acquisition unit 5 through a data line, and the power supply and acquisition unit 5 is used for supplying power to the multi-channel streamer 7 on one hand and recording seismic data acquired by each hydrophone on the other hand.
The depth of a plurality of towlines in the ocean is adjusted by moving the position of the hoop on the photoelectric composite cable; and the seismic source is positioned right below the middle position of the plurality of towing cables by adjusting the distance between the power supply and acquisition unit and the photoelectric composite cable. Thus, after the seismic source is excited, the multiple streamers can record near (zero) offset data, thereby ensuring accurate imaging of shallow structures. The distance adjustable device can directly adopt a Kevlar rope, and the distance between the power supply and acquisition unit and the photoelectric composite cable is changed by adjusting the length of the Kevlar rope.
On the other hand, the sources are located under multiple streamers, providing the possibility of acquiring high signal-to-noise ratio data that is completely immune to ghost interference. FIG. 4 shows different wavefield arrival time relationships when the seismic source and the multi-channel streamers are placed at different water depths. In one implementation of the invention, the water depth is assumed to be 2000m, and the depth separation of the source and the multi-channel streamers is fixed at 200m, as shown in FIG. 4(a), where combination 1: the seismic source depth is 500 m; and (3) combination 2: the seismic source depth is 700 m; and (3) combination: the seismic source depth is 900 m; and (4) combination: seismic source depth 1100 m; and (3) combination 5: the seismic source depth is 1300 m; and (4) combination 6: the seismic source depth is 1500 m; and (3) combination 7: the source depth is 1700 m. The formation reflection in FIG. 4(b) corresponds to the target data, and the time length of the high SNR data depends on the subsequent arrival wavefield time. It can be found through analysis that the direct arrival time of the seismic source ghost waves and the arrival time of the formation reflection have a depassive relationship, when the seismic source depth is shallow (the average depth of water of the seismic source-streamer is not more than half of the depth of water), the data length free from ghost waves mainly depends on the arrival time between the formation reflection and the ghost waves at the hydrophone end, and the effective time length increases as the depth of water of the seismic source increases, such as the combination 1-4. In combinations 5-7, the source-streamer average water depth exceeds half the water depth, at which point the source ghost direct waves begin to affect the formation reflections, and the effective time again lengthens as the source depth continues to increase.
Fig. 5 shows a relationship curve between the time length of the formation reflection not affected by ghost waves and the depth of the seismic source in the model of fig. 4, which is consistent with the analysis result of fig. 4, the time length is firstly linearly increased, then the time window length is sharply decreased after the arrival time of the ghost waves of the seismic source is later than the formation reflection, then the time window length is linearly increased again along with the increase of the depth of the seismic source, and the closer the seismic source is to the water bottom, the longer the effective formation reflection time window length which is not affected by ghost waves can be obtained. However, according to the formula:
Figure BDA0002412765630000061
the closer the seismic source is to the water bottom, the larger the dynamic correction stretch with the same offset distance is, and the smaller the effective superposition track number is. Therefore, when designing the observation system, it is necessary to select the observation system in a targeted manner according to the detection target. In general, the time of flight of the exploration target is ≧ (h-d) when the exploration target is located deep below the seafloor (two-way seismic travel time of the exploration target from the seafloor to the bottom of the sea)2) C), the seismic source can be selectively sunk to be close to the sea bottom, so that a longer effective stratum reflection time window can be obtained, the target stratum is ensured not to be influenced by ghost waves as much as possible, and the depth of the towing cable is required to meet the requirement
Figure BDA0002412765630000062
Where h is the depth of water, d2Is the depth difference between the seismic source and the multi-channel streamer. Otherwise, the seismic source-streamer is placed at the average depth of half the water depth, and the streamer depth is at the time
Figure BDA0002412765630000063
As many effective superposed tracks as possible can be ensured.
FIG. 6 shows different wavefield arrival time relationships when the seismic source and the plurality of streamers are placed at different depths in water. In one embodiment of the invention, the water depth is assumed to be 2000m, as shown in fig. 4(a), where combination pattern 1: source depth 950m, streamer depth 1050 m; combination mode 2: source depth 900m, streamer depth 1100 m; combination mode 3: source depth 850m, streamer depth 1150 m. As can be seen from the data comparison of the graph (b), d2The smaller the effective time window length. However, since the seismic wavelet is not an ideal impulse wavelet generally, and there is often a certain duration, in order to ensure that the effective formation reflection is not affected by the continuation of the wavelet, the system design needs to satisfy:
Figure BDA0002412765630000071
where Δ textIs the seismic wavelet duration.
In summary, the marine seismic exploration method of the invention can be obtained, comprising the following steps:
1) laying a seismic source and a plurality of towing cables according to an exploration target:
first determining that the seismic source depth satisfies
Figure BDA0002412765630000072
Where Δ textThe duration of the seismic wavelet, d2Depth difference between seismic source and multi-channel towing cable, d3The depth of the seismic source from the sea bottom, and c is the sound velocity in water;
when the exploration target is positioned at a deep position below the seabed (the two-way earthquake travel time of the exploration target from the seabed to the bottom is more than or equal to (h-d)2) C) sinking the seismic source to a depth near the sea floor
Figure BDA0002412765630000073
Conversely, streamer depth
Figure BDA0002412765630000074
Where h is the depth of water, d2The depth difference between the seismic source and the plurality of towing cables is obtained; the depths of the plurality of towing cables are fixed by adjusting the position of the hoop on the photoelectric composite cable; finally, adjusting the distance between the hoop and the power supply and acquisition unit to ensure that the seismic source is positioned under the plurality of towing cables;
2) exciting a seismic source 1, transmitting seismic wavelets upwards to a plurality of towropes 7 after the seismic wavelets are reflected at a reflection horizon where an exploration target area is located, and acquiring seismic signals by hydrophones on the plurality of towropes 7; the power supply and acquisition unit 5 supplies power to a plurality of streamers 7 and records seismic data acquired by each hydrophone.
Through the steps, on one hand, the near (zero) offset which is crucial to the imaging of the seabed shallow structure can be recorded, and on the other hand, shallow high-resolution seismic data which are not influenced by ghost waves can be obtained, so that the imaging effect of the seabed shallow structure is effectively improved.
The above-described embodiments are merely preferred embodiments of the present invention, which should not be construed as limiting the invention. Various changes and modifications may be made by one of ordinary skill in the pertinent art without departing from the spirit and scope of the present invention. Therefore, the technical scheme obtained by adopting the mode of equivalent replacement or equivalent transformation is within the protection scope of the invention.

Claims (9)

1. A marine seismic exploration system with a seismic source below a streamer is characterized by comprising a mother ship (3), the seismic source (1), a photoelectric composite cable (2) and a free-standing combined streamer device; the mother ship (3) is connected with the seismic source (1) through the photoelectric composite cable (2); the independent combined towing device is fixed on the photoelectric composite cable (2) through an anchor ear (4);
the independent combined streamer device is positioned above the seismic source (1) and comprises a power supply and acquisition unit (5), a plurality of streamers (7) and a resistance device (8); one end of the power supply and acquisition unit (5) is connected with the hoop (4) through a distance adjustable device, the other end of the power supply and acquisition unit is connected with the multi-channel towing cable (7), the tail part of the multi-channel towing cable (7) is connected with a resistance device (8) for assisting in straightening the towing cable, and the depth of the multi-channel towing cable (7) in the ocean can be adjusted by moving the position of the hoop (4) on the photoelectric composite cable (2).
2. The marine seismic acquisition system with seismic sources below the streamers of claim 1, wherein said freestanding combined streamer device further comprises an auxiliary float (6), said auxiliary float (6) being disposed between said power and acquisition unit (5) and said plurality of streamers (7).
3. The marine seismic acquisition system with seismic sources below streamers according to claim 1, wherein said seismic sources (1) are located directly below the middle of a plurality of streamers (7).
4. The marine seismic acquisition system with seismic sources below the streamers according to claim 1, characterized in that a plurality of hydrophones are uniformly arranged on the plurality of streamers (7), and each hydrophone is connected with the power supply and acquisition unit (5) through a data line.
5. The marine seismic acquisition system with seismic sources below the streamers of claim 1, wherein said plurality of streamers (7) assume a horizontal attitude.
6. The marine seismic acquisition system with seismic sources located below streamers of claim 5, wherein the two-way seismic travel time of the exploration target from the seafloor down is ≧ (h-d)2) At/c, adjusting depth of multi-track streamer
Figure FDA0002412765620000011
Conversely, adjusting the depth of the multi-channel streamer
Figure FDA0002412765620000012
Wherein h isIs the depth of water, d2And c is the depth difference between the seismic source and the multi-channel streamer cable, and the speed of sound in water.
7. The marine seismic acquisition system with seismic sources located below streamers of claim 1, wherein said sources and streamers are arranged such that
Figure FDA0002412765620000013
Where Δ textThe duration of the seismic wavelet, d2Depth difference between seismic source and multi-channel towing cable, d3The depth of the seismic source from the sea bottom, and c is the velocity of sound in water.
8. The marine seismic acquisition system of claim 1, wherein the seismic source is a transducer or a spark source.
9. A marine seismic exploration method based on the system of claim 5, comprising the steps of:
1) laying a seismic source and a plurality of towing cables according to an exploration target:
first determining that the seismic source depth satisfies
Figure FDA0002412765620000021
Where Δ textThe duration of the seismic wavelet, d2Depth difference between seismic source and multi-channel towing cable, d3The depth of the seismic source from the sea bottom, and c is the sound velocity in water;
when the exploration target moves from the seabed to the lower double-stroke earthquake, the walking time is not less than (h-d)2) At/c, the seismic source is sunk and the depth of the multi-channel towing cable is adjusted to meet the requirement
Figure FDA0002412765620000022
Conversely, adjusting the depth of the multi-channel streamer
Figure FDA0002412765620000023
Wherein h is water depth; through adjusting the hoopThe position on the photoelectric composite cable fixes the depth of a plurality of towing cables; finally, adjusting the distance between the hoop and the power supply and acquisition unit to enable the seismic source to be positioned right below the middle position of the plurality of towing cables;
2) exciting a seismic source, transmitting seismic wavelets upwards to a plurality of towlines after the seismic wavelets are reflected at a reflection horizon where an exploration target area is located, and acquiring seismic signals by hydrophones on the plurality of towlines; the power supply and acquisition unit supplies power to the multiple towing cables and records the seismic data acquired by each hydrophone.
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