Seismic pulse generator

Details Seismic pulse generator Seismic pulse generator

1997-09-17

2001-07-17

Dang, Khanh (Department: 2837)

Acoustics

Geophysical or subsurface exploration

Seismic wave generation

C181S117000, C181S118000

Reexamination Certificate

active

06260657

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to seismic pulse generation and, more particularly, to seismic pulse generators for use, for example, in both on-shore and off-shore exploration.
2. Description of the Related Art
One kind of seismic pulse generator with which the invention is concerned, although not exclusively, is that which basically includes a two-chamber device in which a “driver” gas at relatively high pressure in one chamber is employed to generate a shock wave in the other, adjoining, chamber which contains a different gas which is at relatively low pressure. The chambers are not allowed to communicate with each other until the generator is operated. Communication between the two chambers may be prevented for example by means of a releasable shuttle valve member which in the closed position closes an opening between the chambers. When the shuttle valve member is abruptly released from this closed position, to allow communication, a shock wave is generated and propagates in the low pressure chamber as a result of the impact of the high pressure gas onto the low pressure gas. This kind of generator is also referred to as a seismic shock gun. In prior art devices the release of the shuttle valve member from the closed position mentioned above may be initiated by releasing a pressure release member to allow the release of a small portion of the high pressure gas rearwardly from the generator. The pressure release member may be, for example, a poppet-valve or a flap valve as described in Applicant's earlier GB patent specifications nos. 2165945B and 2230860B, respectively.
An object of the invention is to provide a construction of seismic pulse generator which facilitates repeatable firing.
BRIEF SUMMARY OF THE INVENTION
The present invention consists in a seismic pulse generator comprising a body having an internal gas-pressurisable charging chamber, an outlet, and a gas-operated piston valve which is slidably movable within an associated guide to a position to close the outlet when the charging chamber is pressurised with gas to attain a primed ready to fire state for the generator, the piston moving away from the closed position to permit an abrupt release of pressurised gas from the charging chamber through the outlet upon firing of the generator by release of a small portion of gas from a gas pressurised control chamber to atmosphere by means of a solenoid valve assembly mounted on the body, the solenoid valve assembly comprising an annular plunger valve slidably mounted on a valve stem so as to be movable within an annular channel defined between the valve stem and an annular wall, the valve stem having a generally longitudinal gas exhaust passage extending therethrough and terminating at a first opening at the end of the stem remote from the piston, via which first opening the passage communicates with atmosphere, and at least one second lateral opening in the side or peripheral wall of the stem for communicating with the interior of the control chamber, wherein the valve plunger is normally biased to a position on the valve stem whereat the valve plunger closes off the at least one second opening and wherein on actuation of the solenoid valve the plunger slides on the valve stem away from the closed position to allow the at least one second opening to be in communication with the control chamber, whereby the release of the small portion of the pressurised gas from the control chamber to atmosphere can occur.
Conveniently, the passage, via the first opening, opens into a buffer chamber of relatively large volume and having an outlet which vents to atmosphere. This buffer chamber would act to disperse or buffer the effect of the sudden or violent release of the small portion of pressurised gas via the valve stem passage. The advantage of this is that there is a reduction in the pressure and the noise level of the suddenly or violently released gas.
The buffer chamber may in part be defined by a plug or the like fitting in the body of the generator. Conveniently, the plug is adapted to be a removable f it on the body. For example, the plug may be a screw threaded fit in the body. In one embodiment the solenoid valve assembly may be removably secured to the plug, such that when the plug is a removable fit on the body the solenoid assembly can be removed from the body with the plug.
Conveniently, the longitudinal part of the passage in the valve stem and the buffer chamber are substantially in alignment. Such alignment reduces the restriction to, or drag on, the flow of the small portion of gas exhausted from the control chamber to the outlet and thus facilitates the rapid release of the gas from body.
The buffer chamber may serve as a conduit for a portion of an electrical power supply line for the solenoid valve and/or for a portion of a pressuring gas inlet line for the pressurisable control chamber.
Advantageously, a silencer is mounted on the body so that gas released from the pressurisable control chamber via the passage passes through the silencer to atmosphere. The silencer may be of known or traditional design. The provision of the silencer reduces the likelihood of the sound of the firing generator disturbing operators or other people nearby. Preferably, the silencer is in general alignment with the longitudinal part of the passage in the valve stem, and the buffer chamber if present, to further facilitate rapid release of gas from the control chamber.
The solenoid valve assembly may include a gas inlet for communicating with the annular channel with the valve plunger at least in part defining passages which communicate with the control chamber. In one embodiment the annular valve plunger may comprise in its outer peripheral surface channels or grooves which extend generally longitudinally of the plunger and define with the annular wall the passages providing communication between the gas inlet and the control chamber. In an alternative arrangement the valve plunger may have through holes for providing communication between the gas inlet and the control chamber.
The piston guide may be in the form of a cylinder located in the pressurisable chamber and aligned with the outlet associated with the piston valve. An end of the cylinder remote from the outlet may accommodate at least part of the solenoid valve assembly. The control chamber is defined by the cylinder and the opposing solenoid valve assembly and the piston valve when the latter is in its closed position closing off the outlet. The control chamber may communicate with the charging chamber via a bleed hole or resistance-to-flow through hole for example in the wall of the cylinder. Consequently, the supply of pressurised gas to the control chamber can be used to pressurise the charging chamber by virtue of the bleed hole.
In the case where the plug defining a buffer chamber is provided, the cylinder may be secured to the plug. Thus, if the plug is removable from the body, the cylinder as well as the solenoid valve assembly may be removed with the plug when the latter is removed from the body. This facilitates access to the interior of the body and to the solenoid valve assembly, piston valve and cylinder.
The solenoid valve assembly may comprise one or more body parts defining at least one passage which provides communication with the annular channel and with the passage in the valve stem when the solenoid valve is actuated and the at least one lateral opening in the valve stem is uncovered as the valve plunger moves from its closed position.
In one embodiment of the generator, the pressurisable charging chamber adjoins a second chamber with the outlet which is closable by the piston valve opening into the second chamber such that when the generator is “fired” the piston valve moves away from the closed position to uncover the outlet to cause communication between the adjoining chambers and generation of a shock wave in the second chamber in response to the abrupt release of gas from the pressurised charging chamber, the second chamber having means t

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