Frequency conversion marine high pressure air gun seismic source

Abstract

The present invention discloses a variable frequency marine high pressure air gun seismic source. It includes components such as an air gun controller, an air storage chamber, a fixed rod, a sleeve, an initial limit mechanism and a cover, and an adjustable limit block is arranged on the fixed rod. During the excitation process, the length of the air outlet of the air storage chamber is controlled by limiting the limit between the limit block and the limit end of the sleeve. By adjusting the opening length, the air outlet speed can be adjusted to achieve control of the frequency of the excited sub-wave.

Description

Technical Field

[0001] The invention belongs to the field of marine seismic exploration, and in particular relates to a variable frequency marine high-pressure air gun seismic source. Background Art

[0002] Airgun seismic sources are currently the most widely used seismic sources in marine seismic exploration. They are the main seismic sources in marine oil exploration and natural gas hydrate exploration, and they also play an important role in seabed structure and evolution, continental shelf delineation, etc. Airgun seismic sources mainly generate instantaneous pulses and form source sub-waves by injecting high-pressure gas into seawater. The frequency characteristics of this sub-wave are closely related to the speed (gas outlet diameter) of high-pressure gas injected into the water. Figure 1 The source wavelet and its spectrum curve under different outlet aperture conditions are simulated. By comparison, it can be seen that the larger the outlet aperture, the faster the gas release rate, thus producing a higher pulse peak value ( Figure 1 a), correspondingly, more mid- and high-frequency signals will be obtained in the frequency domain, but the aperture size has little effect on the low frequency, such as Figure 1 As shown in b, in the 0-100Hz frequency band that is of most concern to oil and gas exploration, the difference caused by different air outlet diameters is very small. This seismic source with suppressed high-frequency energy is more able to meet the green seismic source design concept for the purpose of marine life protection. On the other hand, in some shallow seabed structure detection, high-frequency energy is needed to improve the resolution of seismic data, such as seafloor massive sulfide deposits SMS (Seafloor Massive Sulfide). SMS is mostly developed in the shallow seabed and is mainly blocky, so a higher resolution is required to effectively identify it. In this case, it is necessary to increase the high-frequency energy as much as possible to improve the resolution.

[0003] Based on the simulation results, in order to ensure that as much high-frequency energy as possible is excited, it is necessary to release the high-pressure gas into the water as quickly as possible, and at this time a sufficiently large outlet aperture is required. There is a contradiction between high resolution (high-frequency energy) and the protection of marine life. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a variable frequency marine high pressure air gun seismic source.

[0005] The technical solution of the present invention is as follows:

[0006] A variable frequency marine high pressure air gun seismic source, comprising an air gun controller, an air storage chamber, a fixing rod, a sleeve, an initial limiting mechanism and a cover;

[0007] The fixing rod is fixedly arranged inside the air storage chamber, and a position-adjustable limit block is arranged on the fixing rod; the sleeve is sleeved on the fixing rod and can move along the fixing rod, and its initial position is limited by the initial limit mechanism;

[0008] The air storage chamber is provided with an air outlet, one end of the sleeve is fixedly connected to the cover, and the other end is a limiting end that cooperates with the limiting block to limit the opening length. After the sleeve is completely retracted to the initial state, the cover can completely cover the air outlet;

[0009] The air gun controller is connected to the limit mechanism through a signal line to realize control; the air storage chamber is connected to an external air compressor through a gas delivery pipeline.

[0010] Preferably, the position of the limit block on the fixed rod is adjusted in advance, such as moving the limit block to a suitable position in advance, and then locking the position of the limit block so that it cannot move relative to the fixed rod.

[0011] Alternatively, the limit block is connected to a set of adjusting rods arranged inside the fixed rod, the position of the limit block relative to the fixed rod is driven by the movement of the adjusting rod, and the position of the limit block is fixed by locking the adjusting rod.

[0012] Alternatively, the air gun controller controls the position of the limit block on the fixed rod through a signal line. For example, the limit block is driven by a motor so that it can move up and down along the fixed rod and can be locked in the fixed rod position.

[0013] Furthermore, an elastic shock-absorbing material, such as a rubber material, is provided at the place where the limiting member contacts the limiting end of the sleeve or at the place where the limiting end of the sleeve contacts the limiting member to reduce the impact.

[0014] Preferably, the initial limiting mechanism is a retractable protrusion arranged on the fixed rod, and the extension and retraction of the protrusion is controlled by the air gun controller.

[0015] Preferably, the gas storage chamber is cylindrical, and the fixing rod is located at its axis. Furthermore, the gas outlet is located at one end surface of the cylinder and is circular; and the gas delivery pipeline is located at the other end surface of the gas storage chamber.

[0016] Furthermore, the gas delivery pipeline is provided with a valve, and the opening of the valve is controlled by an air gun controller.

[0017] When the present invention is working, in the initial state, the sleeve is limited to the initial position by the initial limiting mechanism, and the sealing cover covers the air outlet to be in a sealed state.

[0018] Adjust and lock the position of the limit block on the fixed rod. This position determines the final opening length L of the cover relative to the air outlet. The larger the opening length, the larger the air outlet diameter and the faster the gas release rate, which can produce a higher pulse peak value. Correspondingly, more medium and high frequency signals will be obtained in the frequency domain.

[0019] When the position of the limit block is adjusted, the gas enters the gas storage chamber through the gas delivery pipeline and reaches the required pressure.

[0020] When the seismic source is excited, the air gun controller controls the initial limiting mechanism to cancel the limit, and the sleeve can move along the fixed rod at this time; under the action of high-pressure gas, the sleeve moves relative to the fixed rod and opens the air outlet; when the limiting end of the sleeve moves to the limiting block, it can no longer move, so the opening length L of the cover relative to the air outlet can be controlled according to the position of the limiting block, and then the gas release rate can be controlled to obtain the corresponding frequency.

[0021] If the sleeve needs to be retracted to the initial position, the sleeve can be driven to retract by driving the limit block, and after reaching the set position, the sleeve is restricted by the initial limit mechanism.

[0022] In order to achieve the best balance, the present invention designs a variable frequency high-pressure air gun source. The biggest feature of this design is that it can realize the selection of different excitation modes. The command is transmitted to the aperture control system through the signal transmission system to realize the opening of different air outlet apertures, thereby controlling the air outlet speed and reducing / increasing high-frequency energy. For example, in the collection for the purpose of oil and gas exploration, it is set to a low air outlet speed to minimize the high-frequency energy that is harmful to marine life. In the collection for the purpose of SMS, it is set to a high air outlet speed to ensure the excitation of high-frequency energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Simulated source wavelet under different air outlet aperture conditions (a) and its spectrum curve (b);

[0024] Figure 2 It is a schematic diagram of the state of the variable frequency marine high pressure air gun seismic source waiting to be excited according to the present invention;

[0025] Figure 3 It is a schematic diagram of the source excitation state of the variable frequency marine high pressure air gun of the present invention;

[0026] Figure 4 Schematic diagram of the limit block and the initial limit mechanism in the embodiment. DETAILED DESCRIPTION

[0027] The present invention will be further described below in conjunction with the accompanying drawings.

[0028] like Figure 2 and4 As shown, it is a schematic diagram of the state to be excited of the present invention, a variable frequency marine high-pressure air gun seismic source, including an air gun controller 6, an air storage chamber 1, a fixed rod 2, a sleeve 3, an initial limiting mechanism 5 and a cover 4; the fixed rod 2 is fixedly arranged inside the air storage chamber 1, and a position-adjustable limiting block 7 is provided on the fixed rod 2; the sleeve 3 is sleeved on the fixed rod 2, can be moved along the fixed rod, and its initial position is limited by the initial limiting mechanism 5; the air storage chamber 1 is provided with an air outlet 8, one end of the sleeve 2 is fixedly connected to the cover 4, and the other end is a limiting end that cooperates with the limiting block 7 to realize the opening length limitation, and after the sleeve is fully retracted to the initial state, the cover 4 can completely cover the air outlet 8.

[0029] When in the ready-to-be-activated state, the gas storage chamber is in a sealed state.

[0030] like Figure 4 As shown, in this embodiment, the limit block 7 is connected to a set of adjustment rods 11 arranged inside the fixed rod. The adjustment rod 11 can move up and down, and is connected to the limit block 7 through a slot 12 on the fixed rod, so that the adjustment rod 11 can drive the limit block 7 to move up and down, and the position of the limit block 7 is fixed by locking the adjustment rod 11 through a locking piece 13.

[0031] In this embodiment, the initial limiting mechanism 5 is a retractable convex block arranged on the fixed rod, and the extension and retraction of the convex block is controlled by the air gun controller 6. A concave hole for cooperating with the convex block to limit the initial position is provided on the limiting end 10 of the sleeve 3.

[0032] like Figure 3 As shown, in the excited state, the initial limit mechanism 5 is retracted into the fixed rod; the cover 4 of the sleeve 3 is opened under the action of air pressure, and drives the sleeve 3 to move along the fixed rod, and stops when the limit end 10 reaches the position of the limit block 7. The opening length L at this time is the opening length of this excitation. By adjusting the opening length L, the air outlet speed can be adjusted to achieve control of high-frequency energy.

[0033] remove Figure 4 In addition to the structure shown, the position of the stopper 7 on the fixed rod can also be adjusted in advance. For example, the stopper 7 is moved to a suitable position in advance, and then the position of the stopper 7 is locked so that it cannot move relative to the fixed rod.

[0034] Alternatively, the air gun controller 6 controls the position of the limit block 7 on the fixed rod through a signal line. For example, a rack is provided on the fixed rod, and a gear is provided on the limit block 7. The gear is driven by a motor to move along the rack, so that the limit block 7 can move up and down along the fixed rod 2 and can be locked in position on the fixed rod 2.

[0035] Preferably, an elastic shock-absorbing material, such as a rubber material, is provided at the place where the limiting member contacts the limiting end of the sleeve or at the place where the limiting end of the sleeve contacts the limiting member to reduce impact.

[0036] Preferably, the gas storage chamber is cylindrical, and the fixing rod is located at its axis. Furthermore, the gas outlet 8 is located at one end surface of the cylinder and is circular; and the gas delivery pipeline is located at the other end surface of the gas storage chamber.

[0037] More preferably, the gas delivery pipeline is provided with a valve, and the opening of the valve is controlled by an air gun controller.

Claims

1. A method for exciting a variable frequency marine high pressure air gun source, characterized in that: The variable frequency marine high-pressure air gun seismic source comprises an air gun controller (6), an air storage chamber (1), a fixing rod (2), a sleeve (3), an initial limiting mechanism (5) and a sealing cover (4); The fixing rod (2) is fixedly arranged inside the air storage chamber (1), and a position-adjustable limit block (7) is provided on the fixing rod (2); the sleeve (3) is sleeved on the fixing rod (2) and can move along the fixing rod, and its initial position is limited by an initial limit mechanism (5); The air storage chamber (1) is provided with an air outlet (8); one end of the sleeve (3) is fixedly connected to the cover (4), and the other end is a limit end that cooperates with the limit block (7) to adjust the opening length; after the sleeve is completely retracted to the initial state, the cover (4) can completely cover the air outlet (8); The air gun controller (6) is connected to the initial limit mechanism (5) via a signal line to realize control of the initial limit mechanism (5); the air storage chamber (1) is connected to an external air compressor via a gas delivery pipeline (9); The limit block (7) is connected to an adjusting rod arranged inside the fixing rod, and the position of the limit block (7) relative to the fixing rod is driven by the movement of the adjusting rod, and the position of the limit block (7) is fixed by locking the adjusting rod; The initial limiting mechanism (5) is a retractable convex block arranged on the fixed rod, and the retraction of the convex block is controlled by the air gun controller (6); The excitation method comprises: First, in the initial state, the sleeve is limited to the initial position by the initial limit mechanism, and the cover covers the air outlet to be in a closed state; Adjust and lock the position of the limit block on the fixed rod. This position determines the final opening length L of the cover relative to the air outlet. The larger the opening length, the larger the air outlet diameter and the faster the gas release rate, which can produce a higher pulse peak value. Correspondingly, more medium and high frequency signals will be obtained in the frequency domain. When the position of the limit block is adjusted, the gas enters the gas storage chamber through the gas delivery pipeline and reaches the required pressure; When the seismic source is excited, the air gun controller controls the initial limit mechanism to cancel the limit, and the sleeve can move along the fixed rod at this time; under the action of high-pressure gas, the sleeve moves relative to the fixed rod and opens the air outlet; when the limit end of the sleeve moves to the limit block, it can no longer move, so the opening length L of the cover relative to the air outlet can be controlled according to the position of the limit block, and then the gas release rate can be controlled to obtain the corresponding frequency; If the sleeve needs to be retracted to the initial position, the sleeve is driven to retract by the limit block, and after reaching the set position, the sleeve is restricted by the initial limit mechanism.

2. The excitation method according to claim 1, characterized in that The place where the limit block contacts the limit end of the sleeve or the place where the limit end of the sleeve contacts the limit block is provided with elastic shock-absorbing material.

3. The excitation method according to claim 1, characterized in that The air storage chamber is cylindrical, and the fixing rod is located at the axis thereof.

4. The excitation method according to claim 3, characterized in that The gas outlet (8) is located at one end surface of the cylinder and is circular; the gas delivery pipeline is located at the other end surface of the gas storage chamber.

5. The excitation method according to claim 1, characterized in that The gas delivery pipeline is provided with a valve, and the opening of the valve is controlled by an air gun controller.

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