SU913300A1 - Source of excitation of seismic waves in water reservoirs - Google Patents

Description

The invention relates to the exploration technique, and more specifically to a device for the excitation of seismic waves in the aquatic environment.

Sources of seismic waves are known for offshore exploration in which the energy of compressed gas is used to excite elastic vibrations in the medium under study. The working cycle of these sources usually involves the accumulation of compressed gas in a certain volume, followed by its release into the environment (water).

A pneumatic sound source with a valve controlled by an electromagnetic method includes a chamber into which compressed air is supplied and an electromagnetic valve. The valve closes and opens a hole in the chamber to release compressed air into the test medium. Before filling the chamber with compressed air, the valve is pneumatically pressed against the wall of the chamber, having

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the outlet, and is held in the pressed state by an electromagnet. To create a pulse in a liquid medium, the electric current supplying the electromagnet is interrupted and the valve opens the outlet in the chamber. There is a quick exhaust of compressed gas into the surrounding water and an acoustic wave pz is formed in it due to this.

The disadvantage of this pneumatic source is the presence of significant pulsations of the gas bubble, which distort the seismic records. The implementation of measures aimed at suppressing repeated shocks leads to a cumbersome design of pneumatic sources. In this case, repeated blows are not excluded completely, but only partially weakened.

Known underwater pneumatic

source of seismic pulses, which has a device for reducing the repeated shocks. Main

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elements of the source are a chamber with an outlet, a valve device, a compressed gas supply system and a cam control mechanism. A device for attenuating repeated shocks consists of several vertical pipes with an internal diameter of approximately 10 cm surrounding the source and attached to its casing. The upper ends of the pipes come to the surface of the water, and the lower ones are at the level of the exhaust port of the chamber. Special valves close the lower ends of the pipes, preventing water from entering them. A seismic impulse is created when a compressed gas is rapidly released from the chamber into the surrounding water, while the lower ends of the pipes are inside the expanding gas bubble (2).

However, when the gas pressure inside the bubble becomes less than atmospheric, the valves open, the atmospheric air rushes through the pipes into the bubble, reducing the difference between the hydrostatic pressure and the minimum internal pressure of the bubble, which leads to the weakening of repeated shocks and reduces the frequency of pulsations of the bubble, Hydraulic seismic sources waves make it possible to receive probing bursts | - Nala, uncomplicated pulsations,

In these sources, liquid, usually water, is used as the working medium. Increasing the pressure in the fluid is carried out using the energy of the ship-towing movement, pumping unit for gravitational forces.

The closest to the proposed is a marine seismic source, which uses the effect of a hydraulic hammer. In this source, the impact of water filling an artificial volume created artificially in its thickness is used to excite seismic pulses. The source includes a perforated rigid pipe, over which a sheath of elastic material is hermetically fixed. One end of the pipe is plugged, and the other is connected to a large-diameter pipe with the help of a ventilla, the internal volume of which is 4 times the volume of the perforated pipe. In preparation for the launch of a source in a perforated pipe

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air is slowly pumped under pressure exceeding the hydrostatic pressure at the source’s immersion depth. At the same time elastic

. shell expands. To excite a seismic pulse, a valve opens, controlled electrically from the ship’s side, and the air from the elastic reservoir quickly exits

About in a vacuum tank larger pipe. The hydrostatic pressure of the elastic shell is quickly returned to its original position adjacent to the walls ₅ lerfo ingly pipe and the surrounding water fills the space formed by creating a wavelet in water [3].

The presence of the source tank

₀ large volume and the creation of a vacuum in it significantly complicates and weights its design. Acceleration of the fluid here to get a water hammer is carried out under the action

₅ pressure difference between the hydrostatic pressure of the environment and the pressure in the elastic reservoir. This pressure difference depends on the depth of the source and the magnitude of the vacuum in the tank. For example, with a source’s immersion depth of 10 m and a so-called zero vacuum (with an absolutely empty tank), the pressure difference is only 2 kgf / cm \ Small pressure drops

^15, respectively, lead to low radiation energies per unit working surface of the source.

The purpose of the invention is to increase energy

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Seismic source radiation.

This goal is achieved - the fact that the working chamber is divided by a partition into two parts. Top part

^{45 of the} housing of the working chamber is partially enveloped by a glass-shaped piston, and there are grooves on the housing, and on the piston there are bores that together form a sealed control chamber

⁵⁰ lyeniya and hydraulic damper. Through the hole in the partition of the working chamber passes a rod connecting the upper stakanoobrazny piston, a piston located in the bottom

⁵⁵ parts of the working chamber, and locking

organ. Lower part of the body

the camera is covered by a part of the body of the pickup chamber, which is equipped with

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pneumatic damper and a working agent release unit to the environment, and its bottom is a check valve.

At the same time, the working agent's ejection assembly is a hole in the bottom of the pickup chamber, covered from the outside with a spring-loaded valve that opens after stopping the pickup chamber.

The pneumatic damper is made in the form of a hermetic chamber formed by the housings of the working and expansion chambers, the upper and lower bearings, the chamber cavity communicating with the control chamber.

The lower bearing is elongated, and the seal assembly is placed closer to the end in contact with the cavity of the expansion chamber.

In the initial state, the distance from the hole communicating the cavity of the air damper with the control chamber to the lower bearing seal assembly is greater than the distance from the inner ends of the upper and lower bearings.

In order to increase the contact area. the working chamber with the environment the body of the working chamber and the bottom of the acceleration chamber are provided with support-resistant rings.

The upper part of the working chamber is communicated through the check valve with the environment.

Thanks to this design of the strapping system and source control, the energy intensity is significantly increased, the bubble pulsation is eliminated, and the specific energy intensity is increased.

The drawing shows one of the variants of the concept of the source of excitation of seismic waves in water bodies.

The source consists of · a housing 1 of the working chamber, divided into two parts by a rigid partition 2 with a hole in the center and a shikler 3. On the outer side of the housing 1 there are stepped annular grooves 4 and 5 and annular grooves of sealing elements 6 and 7 on the top. 1, a thread is made to fit the plain bearing 8 with its sealing elements 9 and 10. In the inner cavity of the housing 1 a rod 11 is placed, passing ^!

cheoz central opening of the partition 2, rigidly connected to the piston 12 and the locking body 13. End

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the rod 11 is rigidly connected to the cup-bottom of the piston 14, the inner surface of which is formed with stepped bores, forming conductive ₅ together with respective annular recesses 4 and 5 are driven hermetic chamber 15 and the hydraulic damper 16 (at the lower position of the piston). The tightness of the working chamber 17 is ensured by the sealing elements 18 and 19.

On the housing 1 is movably mounted part of the housing 20 of the acceleration chamber 21,

15 in the upper part of which there is a sliding bearing 22, and in the bottom there is a rigid bottom 23. There are through-holes 24 in the bottom, which are one-sidedly covered with a ₂₀ non-return valve 25. If necessary, to increase the area of contact with the environment, housings 1 and 20 contact disks 26 and 27 can be hung larger than 2 ₅ squares than the bottom 23. The inner surface of the housing 20 and the outer surface of the housing 1 form a closed pneumatic cavity 28 that performs the function of a pneumodempfer,

₃₀ connected by pipeline 29 with

control chamber 15. In addition, the pipe 29 through the remotely controlled valve 30 is connected to the blasting chamber 31. In turn, the blasting chamber 31 through the nozzle 3 communicates with the chamber 32, which communicates with the environment Through a check valve 33. To control the flow of gas fluid ₄₀ uses valves 34-36. There are limiters on the body of the acceleration chamber 37 · In preparing the source for operation, it is necessary to connect the main hoses for liquid and • gas, as well as the electrical cable to power the valve 30. Then the source is placed at a predetermined depth and is considered ready for action.

The source works as follows.

⁵⁰ The valve 34 opens the compressed air supply line from the ship to the control chamber 1 5 and to the gas cavity of the pneumatic cylinder 28. Under the action of this gas

' ⁵ moves the rod with the piston and the locking body relative to the housing 1 so that the cavity 17 is sealed by the locking body 13,

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and the housing 20 moves up to the stop of the stops 37 into the bearing 8. Then the valve 36 is opened and the metered volume of liquid (water) is fed into the chamber 17, then the valve 35 is opened and compressed gas is fed into the chamber 17. The pressure in the chamber 17 rises to a predetermined value (usually in the range of 50-150 atm) and the fluid concentrating in the lower part of the chamber is compressed by gas.

When voltage is applied to the electropneumatic valve 30, chambers 15 and 28 are quickly connected to chamber 31. The pressure in these chambers is leveled, which leads to imbalance of forces on the moving system, and the rod 11 with the piston 12 and the locking member 13 move downwards, sharply opening the working chamber 17. The compressed liquid is ejected from chamber 17 into the cavity of the acceleration chamber 21, where it accelerates and hits the bottom 23. The body of the acceleration chamber 20 together with the bottom 23 moves, forming a shock wave in the environment.

At the initial moment, nothing prevents the movement of the acceleration chamber body except the environment, i.e. All energy resulting from the movement of fluid in the acceleration chamber 21 is transferred to the environment to form a shock wave. Before the start of the movement of the housing 20 in the cavity 28 (in which there was increased pressure holding the housing on the limiters), due to its connection with the chamber 31, the pressure drops sharply. Since the cavity 28 in the initial period of movement remains connected to the chamber 31, and the volume of the latter increases sharply during movement, there is no resistance when the cavity 28 decreases. But as soon as the hole connecting the cavity 28 with the chamber 15 coincides with the body of the sliding bearing 8, the outflow of air from the cavity 28 stops and the deceleration of the movement of the body of the acceleration chamber 20 begins, i.e. pneumodempfer action. The position of the hole connecting the cavity 28 and 15, is determined so that the hole did not reach the seal 10 (in order to prevent seal failure). This condition is satisfied if, in the initial state, the distance from the opening is 913300 8

The distance to the seal assembly 10 is greater than the distance from the inner end of the lower bearing to the inner end of the upper bearing. Removal of waste liquid and gas from the acceleration cylinder is carried out into the environment automatically by means of valve 25. At the same time, the removal rate is selected using the diameter and number of holes 24 such that repeated pulsations are avoided. 3 moment of movement of the housing 20 by the environment valve 25 is pressed to the bottom 23 and the holes 24 55 are closed. As soon as braking begins with the help of the pneumatic cylinder 28, the surrounding water is separated from the bottom 23, forming a cavity with reduced pressure, and since the overpressure in the chamber 21 ₂₀ , the valve 25 opens, the water and gas in the cavity of the chamber 21 go through the holes 24 into the cavity. Thus, ₂₅ release of the cavity of chamber 21 from the working agent occurs and the agent behind the source is filled with this agent, excluding repeated impacts. After release, chamber 21 is closed pneumatically ₍₀ muklapan 30. valves 35 and 36, and the valve 34 is opened - the system returns to its original position and is ready for re-pulse. The energy level of the seismic signal and its spectral composition can be easily adjusted by changing the gas pressure in the working chamber 17 or the ratio in it of the volume occupied by the liquid and gas before the shot.

In a constructive sense, the source is simple and its technical implementation is straightforward. It has a relatively low weight and size, which facilitates and simplifies operation in water areas.

Claims (7)

Claim 1. Source of excitation of seismic waves in reservoirs, containing an overpressure air block, a working and auxiliary chamber, a control and supply system for a worker ⁵⁵ agent, a shut-off member of the working chamber, distinguishing from the fact that, in order to increase energy and radiation, the upper body part 9 913300 10 The working chamber is enclosed by a glass-like piston, and there are stepped grooves on the case, and in the piston there are corresponding bores, which together form a sealed control chamber and a hydraulic damper, the bottom of the piston is connected to a rod passing through the opening of the partition dividing the working chamber cavity into two parts, the piston and the locking member are also rigidly connected to the rod, and the lower part of the working chamber body is movably enveloped by a spraying chamber equipped with a pneumodempfer and an ejection unit of the working agent 15 conductive medium. 2. Source according to claim 1, characterized in that the working agent ejection unit is a hole 20 in the bottom of the pickup chamber, covered from the outside with a spring-loaded valve that opens after the pickup chamber stops. 3. Source according to clause 1, distinguished by 25 th and the second with the fact that the pneumatic damper is made in the form of a hermetic chamber formed by the cases of the working and accelerating chambers and the upper and lower bearings, with the chamber cavity communicating with the control chamber. 4. The source according to the item 3, that is, that the lower bearing is elongated, and the seal assembly is placed closer to the end face in contact with the cavity of the expansion chamber. 5. Source popp. Z 4, characterized in that in the initial state, the distance from the hole that communicates the cavity of the pneumatic damping device with the control chamber to the lower bearing seal assembly is greater than the distance from the inner ends of the upper and lower bearings. 6. The source according to claim 1, characterized in that, in order to increase the contact area of the working chamber with the environment, the housing of the working chamber and the bottom of the distillation chamber are provided with support-stop rings. 7. Source according to claim 1, characterized in that the upper part of the working chamber communicated through a non-return valve with the environment.