Dual-source alternating excitation marine 3D seismic acquisition system

Abstract

The present invention proposes a dual-source alternating excitation marine three-dimensional seismic acquisition system. A first-side spark source and a second-side spark source are towed at the stern of an exploration vessel, and a central control unit and an alternating blasting control module are provided on the exploration vessel. The alternating blasting control module controls the first-side spark source and the second-side spark source to alternately blast, and source data is collected via a data acquisition streamer. The data acquisition streamers are arranged at equal intervals between the first-side spark emission array and the second-side spark emission array. The distance between the first-side spark emission array and the data acquisition streamer closest to it in the horizontal direction is 1 / 2 of the cable spacing, and the distance between the second-side spark emission array and the data acquisition streamer closest to it in the horizontal direction is 1 / 2 of the cable spacing. The present invention provides an ultra-high-resolution shallow three-dimensional seismic acquisition system that can effectively realize three-dimensional detection of strata, structures and targets within about 100m of the shallow seabed.

Description

Technical Field

[0001] The present invention relates to the technical field of ocean exploration, and is a marine seismic acquisition system, in particular to a dual-source alternately excited marine three-dimensional seismic acquisition system. Background Art

[0002] Shallow water development and utilization are an essential component of marine resource development. With the increasing frequency of offshore oil and gas development, the increasing focus on engineering geology for coastal nuclear power plant sites, and the development of offshore wind power, the need for a deeper understanding of the geological environment in the shallow ocean (within 100 meters of the seafloor) is growing. Accurately understanding the structural characteristics of shallow seabed strata and potential hazardous geological types, such as active faults, buried river valleys / channels, shallow gas formations, and bedrock fluctuations, is crucial to these offshore economic activities.

[0003] Marine resource surveys typically rely on marine seismic acquisition systems. Existing ultra-high-resolution shallow 2D seismic acquisition systems can only obtain clear images along a set survey line, but are unable to understand the 3D structural characteristics of shallow targets.

[0004] In addition, most deep-sea marine seismic survey systems in existing technologies are large-scale survey systems with survey cables up to several kilometers long, high excitation energy, and low vertical resolution, making it impossible to achieve high-frequency alternating excitation. Taking the three-dimensional seismic detection system for oil and gas exploration as an example, it mainly targets target layers or structures with a burial depth of more than 1000m. The main frequency of the source is only a few hertz to tens of hertz, the vertical resolution is usually less than 10m, and the receiving surface element is usually 12.5m×25m, which cannot achieve detailed detection and imaging of shallow strata and targets under the seabed. Existing small-scale three-dimensional seismic detection systems use a single small air gun (array) source or a high-energy electric spark source, but seismic imaging still cannot meet the requirements of engineering geological environment cognition, the detection efficiency is not high, and professional geophysical exploration vessels are required as support.

[0005] Therefore, the large-scale deep-sea seismic acquisition system in the existing technology is not suitable for the three-dimensional seismic acquisition system for shallow-sea exploration. Summary of the Invention

[0006] The purpose of the present invention is to address the problems that existing two-dimensional and three-dimensional seismic detection systems are either unsuitable for three-dimensional fine detection of shallow seabed targets or have low detection efficiency, and to propose a three-dimensional seismic acquisition system for shallow sea exploration.

[0007] In order to achieve the above purpose, the technical solutions adopted are:

[0008] A dual-source alternating excitation marine 3D seismic acquisition system includes: a central control unit and an alternating blasting control module disposed on an exploration vessel, wherein the central control unit communicates with the alternating blasting control module to send an excitation control signal to the alternating blasting control module;

[0009] The first side electric spark source and the second side electric spark source are symmetrically arranged on the first side and the second side of the stern of the exploration vessel;

[0010] Data acquisition streamers: arranged at equal intervals between the first-side spark source and the second-side spark source, connected to the central control unit to feed back the collected data to the central control unit;

[0011] The alternate blasting control module sends trigger control signals to the first-side spark source and the second-side spark source alternately to control the first-side spark source and the second-side spark source to blast alternately.

[0012] In some embodiments of the present invention, the first-side spark source comprises a first-side spark emitting array towed at a first side of the stern, and the second-side spark source comprises a second-side spark emitting array towed at a second side of the stern;

[0013] The distance between the first side spark emission array and the nearest data acquisition streamer in the transverse direction is 1 / 2 cable spacing, and the distance between the second side spark emission array and the nearest data acquisition streamer in the transverse direction is 1 / 2 cable spacing.

[0014] In some embodiments of the present invention, the first-side spark source further comprises: a first pulse source and a first-side transmitting cable; the first pulse source is connected to the first-side spark emitting array via the first-side transmitting cable to control the first-side spark emitting array to generate an acoustic wave signal;

[0015] The second-side electric spark source further includes: a second pulse source and a second-side transmitting cable; the second pulse source is connected to the second-side electric spark emission array through the second-side transmitting cable to control the second-side electric spark emission array to generate an acoustic wave signal;

[0016] The first pulse source and the second pulse source are both arranged on the exploration vessel, and both communicate with the alternating blasting control module to receive the pulse trigger signal sent by the alternating blasting control module. Each pulse source has an acoustic signal excitation capability of not less than 2 times per second.

[0017] In some embodiments of the present invention, the collection system further includes a first side traction float and a second side traction float: respectively arranged at the water entry ends of the first side transmitting cable and the second side transmitting cable; the first side electric spark emitting array is arranged on the first side traction float, and the second side electric spark emitting array is arranged on the second side traction float.

[0018] In some embodiments of the present invention, the seismic acquisition system further comprises:

[0019] The first expansion float and the second expansion float are connected to the first side traction float and the second side traction float respectively.

[0020] In some embodiments of the present invention, the data acquisition streamer includes:

[0021] A leader section: communicates with the central control unit and is used for the central control unit to send commands to the acquisition streamer and transmit the acquisition data of the acquisition streamer to the central control unit; the leader section is towed and arranged at the stern of the ship, between the first side launch cable and the second side launch cable;

[0022] Several acquisition cables: each acquisition cable includes a front section, a working section, and a tail section in sequence, wherein the working section is provided with a digital package; the front section of each streamer is connected to a cross station; the front section of each streamer is provided on a connecting cable;

[0023] The cross station of each acquisition cable includes two data cross station interfaces. The cross station interfaces of adjacent acquisition cables are connected in sequence through connecting cables. Moreover, a data cross station interface at the outermost end of the first side is idle, and a data cross station interface of the acquisition cable at the outermost end of the second side is connected to the leading segment.

[0024] In some embodiments of the present invention, the number of acquisition cables located on the first side of the leading section is equal to the number of acquisition cables located on the second side of the leading section.

[0025] In some embodiments of the present invention, the three-dimensional seismic acquisition system further includes a terminal;

[0026] Gigabit Ethernet is used for communication between the terminal and the central control unit;

[0027] The central control unit and the data cross station use LVDS network cable for transmission;

[0028] The data cross station and the digital package communicate with each other using the RS485 bus.

[0029] In some embodiments of the present invention, the cable spacing is 6 meters, the number of acquisition cables is 6, and when lateral coverage is not required, the survey line spacing is 36 meters. When lateral coverage is required, the survey line spacing is calculated according to the following formula:

[0030] D=36 / n

[0031] Where D is the survey line spacing in meters; n is the required number of lateral coverages.

[0032] In some embodiments of the present invention, the shot line distance is preferably 36m or 18m.

[0033] Compared with the prior art, the advantages and positive effects of the present invention are:

[0034] In response to the increasing demand for understanding shallow marine geological conditions and the challenges of existing technologies, this invention provides an ultra-high-resolution shallow 3D seismic acquisition system that can effectively perform 3D detection of strata, structures, and targets within 100 meters below the seafloor. The imaging bin size can reach 1m x 3m, and the vertical resolution can reach sub-meter levels. This system enables ultra-high-resolution 3D seismic detection of shallow seabed layers, thereby obtaining the fine structure of shallow seabed strata and structures.

[0035] (1) The system uses a low-energy dual electric spark source with a main frequency of no less than 700 Hz. Compared with the existing three-dimensional seismic system, the vertical resolution has been greatly improved and can reach the sub-meter level.

[0036] (2) The system adopts a dual-source intra-channel alternating excitation mode with a shot spacing of 1 / 2 the track spacing. The lateral coverage of two adjacent shot receiving points can reach 33m. Combined with the shot point-receiver point plane configuration in which the transmitting array is placed outside the acquisition array, the coverage range of the receiving points can be effectively improved. Compared with the single source (air gun, BOOMER or spark source) used in existing small-scale 3D seismic systems in China and abroad, the exploration efficiency is greatly improved.

[0037] (3) By making full use of the characteristics of different transmission technologies and adopting a three-level cascade data transmission system consisting of Gigabit Ethernet, LVDS and standard RS485, it can effectively ensure the high-data transmission of seismic data, ensure high-density excitation of the earthquake source, and achieve 1m shot spacing, thereby realizing more precise seismic detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a schematic diagram of the structure of the marine 3D seismic acquisition system of the present invention;

[0039] Figure 2a This is the circuit diagram of the source control module;

[0040] Figure 2b This is the circuit and trigger logic diagram of the source control module

[0041] Figure 3 It is a three-level cascade topology structure for the data transmission system;

[0042] Figure 4 This is the logical structure diagram of the central control unit;

[0043] Figure 5 This is a diagram showing the connection between the acquisition cable, the traction float, and the expansion float;

[0044] Figure 6a The coverage of receiving surface elements when the shot line distance is 36m and the channel is alternately excited;

[0045] Figure 6bThe coverage of receiving surface elements when the shot line distance is 18m and the channel is alternately excited;

[0046] Figure 7a Schematic diagram of the coverage range when the seismic source is set at the receiving point outside the acquisition array during dual-source excitation;

[0047] Figure 7b Schematic diagram of the coverage range when the source is set at the middle receiving point of the acquisition array during dual-source excitation;

[0048] Figure 7c Schematic diagram of the coverage range of receiving points when a single source is excited.

[0049] 1- Exploration vessel;

[0050] 201- Central Control Unit, 202- Alternate Firing Control Module;

[0051] 301-first side launch cable, 302-second side launch cable;

[0052] 401 - first side electric spark emission array, 402 - second side electric spark emission array;

[0053] 501-first side traction float, 502-second side traction float;

[0054] 601-first expansion float, 602-second expansion float;

[0055] 701-leading section, 702-first side connecting cable, 703-second side connecting cable, 704-front bullet section, 705-working section, 706-tail bullet section, 707-digital package;

[0056] 8-Data cross station;

[0057] 901-first pulse source, 902-second pulse source;

[0058] 10-Terminal. DETAILED DESCRIPTION

[0059] The present invention is described in detail below by way of exemplary embodiments, but it should be understood that elements, structures, and features of one embodiment may be beneficially combined in other embodiments without further description.

[0060] It should be noted that the terms "first" and "second" are used for descriptive purposes only and are not used to imply relative importance.

[0061] The present invention provides a dual-source alternately excited marine three-dimensional seismic acquisition system, which is mainly used for fine detection of shallow seabed targets.

[0062] The dual-source alternating excitation marine 3D seismic acquisition system includes an exploration vessel 1, a central control unit 201, and an alternating shot control module 202, disposed on the exploration vessel 1. The central control unit 201 communicates with the alternating shot control module 202 to send excitation control signals to the alternating shot control module 202. The system further includes the following structure.

[0063] The first side electric spark source and the second side electric spark source are symmetrically arranged on the first side and the second side of the stern of the exploration vessel;

[0064] Data acquisition streamers: arranged at equal intervals between the first-side spark source and the second-side spark source, connected to the central control unit to feed back the collected data to the central control unit;

[0065] The alternate blasting control module sends trigger control signals to the first-side spark source and the second-side spark source alternately to control the first-side spark source and the second-side spark source to blast alternately.

[0066] As a specific implementation, the implementation structures of the first-side spark source and the second-side spark source are as follows.

[0067] The first-side spark source includes a first pulse source 801, a first-side transmitting cable 301, and a first-side spark array 401. The second-side spark source includes a second pulse source 802, a second-side transmitting cable 302, and a second-side spark array 402. The first-side spark array 401 is towed and arranged on the first side of the hull, while the second-side spark array 402 is towed and arranged on the second side of the hull.

[0068] The first pulse source 901 and the second pulse source 902 are arranged on the exploration vessel, both communicate with the source control module, receive pulse control signals, are connected to the first side transmitting cable 301 and the second side transmitting cable 302, and send pulse drive signals. The pulse drive signal sent by each pulse source has an acoustic signal excitation capability of not less than 2 times / second; the alternating blasting control module 202 starts triggering control of the first pulse source 901 or the second pulse source 902 when receiving the excitation control signal from the central control unit 201.

[0069] The first side spark emitting array and the second side spark emitting array are symmetrically arranged on the first side and the second side of the stern, respectively communicating with the first pulse source 901 and the second pulse source 902, receiving the excitation signals of the pulse sources on the corresponding sides to generate acoustic wave signals.

[0070] In some embodiments of the present invention, the first-side spark emitting array and the second-side spark emitting array are specifically implemented through the following structure.

[0071] The first side electric spark emission array includes: a first side emission cable 301 and a first side electric spark emission array 401;

[0072] The second side spark emitting array includes: a second side emission cable 302 and a first side spark emitting array 402;

[0073] The first side transmitting cable 301 and the second side transmitting cable 302 are symmetrically dragged and arranged on the first and second sides of the stern, responsible for energy transmission. The first side of the stern corresponds to the starboard side of the ship, and the second side corresponds to the port side of the ship.

[0074] The first side electric spark emitting array 401 and the second side electric spark emitting array 402 are respectively connected to the first side transmitting cable 301 and the second side transmitting cable 302 to generate respective pulse driving signals;

[0075] Data acquisition streamers: arranged at equal intervals between the first spark source array 401 and the second spark source array 402, connected to the central control unit 201, which collects data from the data acquisition streamers;

[0076] The source control module sends pulse control signals alternately to the first pulse source 901 and the second pulse source 902 to control the first electric spark source array 401 and the second electric spark source array 402 to fire alternately. Since the excitation frequency is fast, which can reach 2 times / second, it is possible to achieve excitation with a shot spacing of 1 / 2 track spacing.

[0077] The first-side spark array 401 and the second-side spark array 402 are placed outside the data acquisition streamer array, and the lateral distance between the first-side spark array 401 and the nearest data acquisition streamer in the acquisition array is 1 / 2 cable pitch: the lateral distance between the first-side spark array 401 and the nearest data acquisition streamer is 1 / 2 cable pitch, and the lateral distance between the second-side spark array 402 and the nearest data acquisition streamer is 1 / 2 cable pitch. This shot point-receiver point planar configuration can effectively improve exploration efficiency and expand detection range in the 1 / 2 channel spacing shot mode. Figure 7a 、 Figure 7b and Figure 7c When the cable spacing and the number of streamers are the same, setting two seismic sources can improve the coverage of the receiving point compared to setting one seismic source; setting the seismic source on the outside of the streamer can improve the coverage of the receiving point compared to setting it in the middle of multiple streamers.

[0078] After the pulse source sends a pulse signal, the signal is transmitted to the spark source arrays on both sides via the transmitting cables on both sides. Since the alternating blasting control module 202 alternately sends pulse trigger signals to the first pulse source 901 and the second pulse source 902, the first side spark emission array 401 and the second side spark emission array 402 are alternately excited to generate seismic wave signals. To meet the needs of rapid blasting (source excitation interval less than 1 second) during seismic acquisition, the pulse source has an excitation capacity of no less than 2 times / second. To achieve ultra-high-resolution shallow-layer detection, the main frequency of the spark source wavelet should be no less than 700Hz. The source system can achieve intra-channel excitation (1 / 2 channel spacing) at a ship speed of 4 knots, while the shot spacing in existing three-dimensional seismic detection is an integer multiple of the channel spacing (1, 2, ...).

[0079] The source control module is the core unit that controls the alternating discharge of two pulse sources. Its control circuit and timing are as follows: Figure 2a and Figure 2b As shown. The digital integrated circuit 74HC74 is a rising edge triggered D-type flip-flop. When the trigger signal detects a jump from low level to high level at the input terminal (point A) of the D-type flip-flop, the output terminal (point B) of the D-type flip-flop flips over. The digital integrated circuit 74HC211 is a dual monostable multivibrator (Schmitt trigger). The output terminal (point B) of the D-type flip-flop is connected to the two input terminals (points 1 and 2) of the 74HC211. and 2B) are connected as the input terminals of two Schmitt triggers, where 2B is the falling-edge trigger input of Schmitt trigger #1, and 2B is the rising-edge trigger input of Schmitt trigger #2. Connect the outputs of the two Schmitt triggers (points C and D) to two optocouplers. On the rising edge of point B, a pulse is generated at point C, which outputs a trigger signal through the optocoupler. On the falling edge of point B, a pulse is generated at point D, which outputs a trigger signal through the optocoupler. This way, the input pulse at point A is evenly distributed to the two outputs, achieving alternating excitation of the source.

[0080] The data acquisition streamer is located laterally between the first side spark emitting array 401 and the second side spark emitting array 402, and is located behind the first side spark emitting array 401 and the second side spark emitting array 402 in the direction of travel of the survey vessel. It is responsible for receiving, collecting and transmitting seismic signals to analyze the characteristics of shallow seabed targets.

[0081] In some embodiments of the present invention, the acquisition system further includes a first side traction float 501 and a second side traction float 502: which are respectively arranged at the water-entering ends of the first side transmitting cable 301 and the second side transmitting cable 302; the first side electric spark emission array 401 is arranged on the first side traction float 501, and the second side electric spark emission array 402 is arranged on the second side traction float 502.

[0082] In some embodiments of the present invention, the seismic acquisition system further comprises:

[0083] The first expansion buoy 601 and the second expansion buoy 602 are connected to the first side traction buoy 501 and the second side traction buoy 502 respectively.

[0084] In this invention, an expansion system is constructed using a towing buoy and an expansion buoy. The towing buoy and expansion buoy on each side together form an expander. The expander generates tension when pulled by the current and the hull. This tension forces the towing appendage and the collection array to reach a predetermined position and stabilize. The transmitting array is positioned behind the towing buoy, ensuring proper spacing between the collection arrays and addressing the required distance between the collection tow cable and the transmitting array.

[0085] The expansion float has an 850 kg force and a 4.5 knot expansion capability, allowing the entire acquisition array to be deployed. The combined weight of the expansion float and towing float in air does not exceed 400 kg, making it suitable for operation on non-specialized geophysical survey vessels. When the expansion system is deployed, the collection streamers are spaced 6 meters apart, the transmitting array is located 4 meters behind the towing float, and the horizontal distance (perpendicular to the direction of travel) between the expansion float and the nearest streamer on the adjacent side is 3 meters.

[0086] In some embodiments of the present invention, the data acquisition streamer includes:

[0087] A leading section 701: 100m in length, communicating with the central control unit, towed at the stern, located between the first side launch cable 301 and the second side launch cable 302;

[0088] Taking the connecting cable as an example for easy understanding, in the present invention, the connecting cable is defined as the first side connecting cable 702 and the second side connecting cable 703 according to the position of the connecting cable: they are respectively arranged between the leading section 701 and the first side traction float 501, and between the leading section 701 and the second side traction float 502; the first side connecting cable 702 and the second side connecting cable 703 play the role of connection and support, and are used to connect the adjacent collection cables on each side.

[0089] Several acquisition cables: Each acquisition cable includes a front section, a working section and a tail section in sequence. The front section of each tow cable is connected to the cross station. The front section of each tow cable is set on the connecting cable for collecting and transmitting acquisition data. The working section 705 is provided with a digital package.

[0090] In some embodiments of the present invention, the number of acquisition cables located on the first side of the leading section 701 is equal to the number of acquisition cables located on the second side of the leading section. The acquisition cables located on the first side of the leading section 701 are connected via a first-side connecting cable 702, while the acquisition cables located on the second side of the leading section 702 are connected via a second-side connecting cable 703. In this configuration, the leading section 701 is centrally located, reducing signal interference. In practical applications, the leading section 701 can also be positioned closer to the port or starboard side of the ship.

[0091] Each cross station 8 includes two data interfaces 801, and adjacent cross station interfaces are connected in sequence, and one data cross station interface of the acquisition cable at the outermost end of the second side is connected to the leading segment, and one data cross station interface at the outermost end of the first side is idle. Figure 3 Each acquisition cable includes multiple data packets, which are connected in series to aggregate and transmit the collected seismic data. The first data interface 801 at the crossover station at the front end of the acquisition cable on the first side is idle. The second data interface 801 is connected to the first interface 801 at the crossover station at the front end of the second acquisition cable. The second interface 801 is connected to the first interface 801 at the crossover station at the front end of the third acquisition cable. The other acquisition cables are connected in sequence. The second crossover station interface 801 of the acquisition cable at the outermost end of the second side is connected back to the leader section 701 and fed back to the central control unit 201 via the leader section 701.

[0092] Specifically, in this embodiment of the present invention, three acquisition cables are installed on the first-side connecting cable 702, and three acquisition cables are installed on the second-side connecting cable 703, for a total of six acquisition cables. Each cable has a front section 704 of 10 meters, a working section 705 of 30 meters, and a tail section 706 of 10 meters. Each acquisition cable contains 16 channels, each composed of three hydrophones, with 2 meters of channel spacing. A digital packet is created for every four channels. The digital packet converts the analog seismic signals received by the hydrophones into digital signals according to the acquisition command and transmits the data upstream. To capture weak seismic signals, a 32-bit digital-to-analog conversion module is used in the digital packet.

[0093] In some embodiments of the present invention, the 3D seismic acquisition system further includes a terminal;

[0094] The terminal 10 communicates with the central control unit 201 using Gigabit Ethernet, and can call data from the central control unit 201;

[0095] The central control unit 201 and the data cross station use LVDS network cable for transmission;

[0096] RS485 bus communication is used between the data cross station 8 and the digital package 707.

[0097] Specifically, ultra-high resolution shallow 3D data acquisition has the characteristics of small shot interval and small sampling interval. To adapt to the above characteristics, the data transmission system adopts a three-level cascade topology ( Figure 3 The terminals can be located on the coast. The first layer of communication is between the terminal 10 and the central control unit 201, using Gigabit Ethernet. The second layer of communication is between the central control unit 201 and the data cross station, and between the cross stations, using standard Category 6 LVDS transmission with a custom transmission protocol. The third layer of communication is between the data cross station and the digital packets, using standard RS485 transmission with a custom transmission protocol. Physically, the data transmission system primarily consists of a 100m-long preamble, a cross station, connecting cables, and corresponding communication modules.

[0098] In addition to the source control module and data module described above, the central control unit 201 also includes a system control module, a communication module, and a power supply module. The data module receives data from the six streamers and stores it on the hard drive. It also issues acquisition instructions, sends downlink clock commands, and powers the acquisition streamers. The system control module primarily comprises a master-slave controller module, a trigger controller module, a GPS resolver module, an LVDS transmitter module, an LVDS receiver module, a Gigabit Ethernet controller module, and a data checker module.

[0099] In some embodiments of the present invention, the cable spacing is 6 meters, the number of acquisition cables is 6, and when lateral coverage is not required, the survey line spacing is 36 meters. When lateral coverage is required, the survey line spacing is calculated according to the following formula:

[0100] D=36 / n

[0101] Where D is the survey line spacing in meters, and n is the required number of lateral coverages. Lateral coverage here means that a given area can be covered by surveys while the survey vessel is operating on different lines.

[0102] In some embodiments of the present invention, the shot line distance is 36m or 18m.

[0103] The shot line distance refers to the distance between two adjacent shot lines during seismic work. The preferred shot line distance for data acquisition is 36m or 18m. When the shot line distance is 36m and the shot is fired at 1 / 2 intervals, the receiving point has 8 coverages in the vertical direction and no coverage in the horizontal direction; when the shot line distance is 18m and the shot is fired at 1 / 2 intervals, the receiving point has 8 coverages in the vertical direction and 2 coverages in the horizontal direction, which can achieve a total of 16 coverages. The bin coverage is as follows: Figure 6a and Figure 6b ,in Figure 6b The area framed in the middle is the range of the surface element with a horizontal coverage of 2.

[0104] The process of collecting offshore 3D seismic data using the seismic acquisition system provided by the present invention is as follows.

[0105] The 3D seismic data acquisition process mainly includes: ① all wet-end equipment is put into water; ② all interfaces are connected and the system is powered on and self-tested; ③ the terminal acquisition software is configured with acquisition and recording parameters, and after success, the command is issued to start acquisition; ④ seismic data is collected along the set survey line; ⑤ after completing the designed survey line and stopping acquisition, the wet-end equipment is recovered.

[0106] The wet end equipment primarily consists of six collection streamers, a leader, an EDM array, an expander, and a towing float. The launch and recovery of the wet end equipment requires the coordinated operation of the survey vessel's A-frame and the expander system's winch. The process is as follows:

[0107] (1) First, place the expansion float and the traction float on one side (either the port or starboard side) into the water, and at the same time as the traction float, the electric spark emission array is also placed into the water.

[0108] (2) After the expansion float enters the normal working state, fix the middle towing rope, put the outermost collection towline on the same side of the expansion float into the water, and connect it to the predetermined shackle of the transverse cable.

[0109] (3) Then, a second collection towline on the same side, from outside to inside, is lowered into the water and connected to the transverse cable in the same manner as the first towline.

[0110] (4) After releasing the expansion float, traction float and spark launch array on the other side into the water, release two collection tow cables in sequence according to the previous method.

[0111] (5) After the above four tow cables enter the water, the expander is slowly released backwards by the towing winch, and the two middle tow cables are put into the water at the same time, and finally to the predetermined position. After the expansion system is deployed, the positional relationship between the acquisition array and the transmission array is as follows: Figure 5 The two telephone transmitter arrays towed behind the towing buoy are located outside the collection array composed of 6 collection streamers, with a distance of 36m between them.

[0112] (6) The wet end equipment recovery process is the opposite of the water entry process.

[0113] During seismic data acquisition, the OCC trigger module calculates the next shot firing time based on GPS data and the set shot spacing. Based on this calculation, it then synchronously sends a TTL signal to the digital package and source control module. The source control module automatically sends these TTL signals alternately to the two pulse sources, stimulating the acoustic source signals through the port and starboard transmitting arrays. During in-channel firing, the shot spacing is set to half the towline spacing, or 1 meter. At a ship speed of 4 knots, the time between shots is approximately 0.5 seconds.

[0114] The energy of the electric spark source can be selected as needed, but the energy settings of the left and right sources need to be kept consistent.

[0115] During seismic acquisition, the offset distance varies from 6m to 36m in the longitudinal direction (along the direction of the survey line), and from 3m to 30m in the transverse direction (perpendicular to the direction of the survey line).

[0116] In the acquisition parameter setting, the sampling frequency is not less than 4kHz and the record length is not more than 300 milliseconds.

[0117] During seismic data acquisition, the sea condition should be less than level 3, and the ship speed should be maintained at 2-4 knots, adjusted according to the status of the expander and the tide; the ship speed should be appropriately reduced when turning, and the turning radius should be no less than 500m; the RGPS can be fixed on the towing float to locate the shot point.

[0118] The above description is merely a preferred embodiment of the present invention and does not constitute any other form of limitation to the present invention. Any person skilled in the art may utilize the technical contents disclosed above to change or modify them into equivalent embodiments with equivalent changes for application in other fields. However, any simple modification, equivalent change, and modification of the above embodiments made in accordance with the technical essence of the present invention without departing from the technical solution of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A dual-source alternating excitation marine 3D seismic acquisition system, characterized by: include: A central control unit and an alternating blasting control module are provided on the exploration vessel, wherein the central control unit communicates with the alternating blasting control module to send an excitation control signal to the alternating blasting control module; The first side electric spark source and the second side electric spark source are symmetrically arranged on the first side and the second side of the stern of the exploration vessel; Data acquisition streamers: arranged at equal intervals between the first-side spark source and the second-side spark source, connected to the central control unit to feed back the collected data to the central control unit; The alternate blasting control module sends a trigger control signal to the first-side spark source and the second-side spark source alternately to control the first-side spark source and the second-side spark source to alternately blast; The first-side spark source includes a first-side spark emitting array towed at a first side of the stern, and the second-side spark source includes a second-side spark emitting array towed at a second side of the stern; The distance between the first-side spark emitting array and the nearest data acquisition streamer in the transverse direction is 1 / 2 of the cable spacing, and the distance between the second-side spark emitting array and the nearest data acquisition streamer in the transverse direction is 1 / 2 of the cable spacing; The first side electric spark source further includes: a first pulse source and a first side transmitting cable; the first pulse source is connected to the first side electric spark transmitting array through the first side transmitting cable to control the first side electric spark transmitting array to generate an acoustic wave signal; The second-side electric spark source further includes: a second pulse source and a second-side transmitting cable; the second pulse source is connected to the second-side electric spark emission array through the second-side transmitting cable to control the second-side electric spark emission array to generate an acoustic wave signal; The first pulse source and the second pulse source are both arranged on the exploration vessel, and both communicate with the alternating blasting control module to receive the pulse trigger signal sent by the alternating blasting control module. Each pulse source has an acoustic signal excitation capability of not less than 2 times per second. The data acquisition streamer comprises: A leader section: communicates with the central control unit and is used for the central control unit to send commands to the acquisition streamer and transmit the acquisition data of the acquisition streamer to the central control unit; the leader section is towed and arranged at the stern of the ship, between the first side launch cable and the second side launch cable; Several acquisition cables: each acquisition cable includes a front section, a working section, and a tail section in sequence, wherein the working section is provided with a digital package; the front section of each streamer is connected to a cross station; the front section of each streamer is provided on a connecting cable; The cross station of each acquisition cable includes two data cross station interfaces. The cross station interfaces of adjacent acquisition cables are connected in sequence through connecting cables. Moreover, a data cross station interface at the outermost end of the first side is idle, and a data cross station interface of the acquisition cable at the outermost end of the second side is connected to the leading segment.

2. The dual-source alternating excitation marine 3D seismic acquisition system according to claim 1, characterized in that: The acquisition system further includes a first side traction float and a second side traction float: respectively arranged at the water-entering ends of the first side transmitting cable and the second side transmitting cable; the first side electric spark emitting array is arranged on the first side traction float, and the second side electric spark emitting array is arranged on the second side traction float.

3. The dual-source alternating excitation marine 3D seismic acquisition system according to claim 2, characterized in that: The number of acquisition cables located on the first side of the leading section is equal to the number of acquisition cables located on the second side of the leading section.

4. The dual-source alternating excitation marine 3D seismic acquisition system according to claim 1 or 3, characterized in that: The three-dimensional seismic acquisition system further includes a terminal; Gigabit Ethernet is used for communication between the terminal and the central control unit; The central control unit and the data cross station use LVDS network cable for transmission; The data cross station and the digital package communicate with each other using the RS485 bus.

5. The dual-source alternating excitation marine 3D seismic acquisition system according to claim 1, characterized in that: The seismic acquisition system further comprises: The first expansion float and the second expansion float are connected to the first side traction float and the second side traction float respectively.

6. The dual-source alternating excitation marine 3D seismic acquisition system according to claim 1, characterized in that: The cable spacing is 6 meters, and the number of acquisition cables is 6. When lateral coverage is not required, the survey line spacing is 36 meters. When lateral coverage is required, the survey line spacing is calculated according to the following formula: In the formula Survey line spacing, in meters; is the required number of horizontal coverages.

7. The dual-source alternating excitation marine 3D seismic acquisition system according to claim 6, characterized in that: The gun line distance is 36m or 18m.

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