Methods and devices are disclosed for generating acoustic pulses in a water or land medium, e.g., for use in seismic investigations. The pulse amplitudes, waveshapes, and frequencies can be controlled by signals that may originate at a remote location. Compressed gas is confined at high pressure in a valve chamber (12, 194). An initiating signal causes the opening of a passage (54, 56, 192) from the chamber into the medium to initiate the rise of a pressure pulse therein. A second signal causes the closing of the passage in a manner such that the initial rise of the pressure pulse is limited by the closure of the passage. In one device, the passage is opened by one sleeve valve member (60) and closed by another sleeve valve member (58). In another device the passage is opened by a sleeve valve member (196) whose motion to open the passage is arrested substantially instantaneously by transferring its momentum to a momentum exchange sleeve (246) that is then gradually decelerated. The passage may be closed by the same sleeve valve member (196) whose motion to close the passage is arrested substantially instantaneously by transferring its momentum to a second momentum exchange sleeve (220) that is then gradually decelerated.
A dual shuttle air gun for generating maximum acoustic output for seismic testing having a housing with an air chamber formed therein and a chamber opening that opens 360 degrees around the periphery of the body is disclosed. The two shuttles are positioned around the housing axially displaced from each other, but close enough to allow the end faces of each shuttle to come into close proximity with each other. When the air gun is fired by the activation of a solenoid, compressed air flows into a firing chamber formed between the first shuttle and the housing causing the first shuttle to begin opening. When the first shuttle moves, the end faces of the two shuttles are exposed to the compressed air from the primary chamber. This causes the two shuttles to rapidly move away from each other providing for very quick release of the stored compressed air. When the solenoid is deactivated, the two shuttles are forced back into a prefire condition over the 360 degree opening.
A large-diameter, cylinder-shuttle airgun for seismic uses has a cylinder shuttle configured as a hollow, elongated cylinder body of revolution with an inwardly-facing cylinder guide surface and having two outwardly-extending, axially-spaced annular flanges. These two annular flanges are an operating flange at an upper end of the body of revolution and a firing flange at an intermediate region thereof. A cylinder skirt extends down below the firing flange, and the cylinder shuttle has an overall axial length L. The firing flange has a perimeter of outside diameter OD, and the ratio of L to OD is at least about 1 to 1. A cylinder housing of the airgun has a main inner cylinder structure encircled by the cylinder shuttle. This main inner cylinder structure may have an axial passageway of sufficient diameter for passing at least one compressed air hose and at least one multi-conductor electric cable axially therethrough. The housing provides an annular operating chamber for receiving the operating flange therein and has an annular firing chamber with removable interchangeable annular chamber walls for changing volume of the annular firing chamber. The skirt on the cylinder shuttle extends down into the firing chamber. The housing defines an annular discharge port positioned intermediate the operating and firing chambers and extending 360.degree. around the axis of the housing. By employing a firing flange of large OD, a Torus bubble is produced of large "C" radius in relation to its axis of revolution which provides enhanced peak pressure output and improved PBR compared with a standard airgun.
The liquid slug projector apparatus is entirely pneumatically operated. It comprises a generator having a main housing whose main port fluidly communicates with a liquid body. A first shuttle and a second shuttle are slidably mounted inside the main housing. The first shuttle forms with the main housing a slug chamber for confining therein a liquid slug. A pneumatic source together with a pneumatically-operated valve cyclically cause the shuttles to move relative to or in locked condition with each other, thereby applying during each cycle of operation an abrupt propulsion force to the confined liquid slug which becomes expelled as a very high-velocity liquid jet through the main port.
A dual chamber seismic air gun which discharges both chambers simultaneously to counterbalance the reactive forces generated by the discharges. The chambers are symmetrical within the housing of the gun so that the movement of the internal parts during operation also counterbalance each other. The gun is mounted coaxially on the air supply of a seismic array to provide a good profile for towing.
A seismic energy source air gun has a body with an air chamber formed therein that opens 360 degrees around the periphery of the body. A sleeve-type shuttle covers the opening in a pre-fire condition. When the air gun is fired, the shuttle moves rapidly away from the opening providing a large area for compressed air held in the chamber to escape. This very quick release maximizes the acoustic output. The movement of the shuttle is ultimately controlled by a solenoid which, when activated, causes the shuttle to move away from the 360 degree opening and when deactivated permits the shuttle to move back into the pre-fire position over the 360 degree opening.
