Geco A.s.

Schlumberger Technology Corporation

Jan-Age Langeland

Einar Gjestrum

Simon Hastings Bittleston

Clive T Snook

Gunnar Parmann

Nils Lunde

Rolf Bjerkoy

Cato Bjelland

Julius Bendiksen

Rolf Bjerk Y

A seismic streamer comprises a substantially solid core having many of the main components of the streamer, namely hydrophones, electronics modules for digitising the outputs of the hydrophones, the main optical and electrical conductor bundles and Keviar strength members, embedded in it. The core also contains a large number of foam buoyancy elements. An outer skin surrounds the core, defining an annular gap around the core, and this annular gap is filled with open-celled polyurethane foam saturated with kerosene. The capsules containing the hydrophones communicate with the annular gap around the core, so that the kerosene can enter the capsules, each of which contains an open-celled polyurethane foam sheath to cushion the hydrophone. In an alternative construction, made possible by using the buoyancy elements in the core to render the core approximately neutrally buoyant in water, the outer skin and the polyurethane foam are omitted, and the core is used on its own as a solid streamer.

Method of making a marine seismic streamer

A method for calibration of hydrophone groups is based on the use of a Helmholtz resonator, which is arranged such that a seismic streamer (Il) or sections thereof can be placed in the resonator's cavity (1) and connected via a hydrophone group selector (9) to a signal analyzer (6). A sound source (3) provided in the Helmholtz resonator is driven by a white noise signal at a frequency close to the resonator's resonance frequency. The sensitivity of the hydrophones in the respective hydrophone group (10) which is to be calibrated is determined by passing the hydrophone signals to the signal analyzer (6) where they are compared with a reference signal from a reference transducer (5), e.g., a measuring microphone, provided in the resonator. The Helmholtz resonator is designed as a drum-shaped vessel (1) provided with a funnel-shaped neck which constitutes an acoustic horn (2) and creates an impedance matching between the vessel (1), which constitutes a resonant cavity, and an electrodynamic transducer, which constitutes the sound source (3), provided at the smaller end of the horn (2). For the measurements a measuring microphone (5) is provided inside the cavity together with, e.g., a reel (4) or drum on which are wound sections of a seismic streamer, or a seismic streamer (11), whose hydrophone groups (10) are to be calibrated.

Calibration of seismic streamers in a Helmholz resonator

An arrangement for deployment and towing of a plurality of seismic cables (2) in parallel and at a mutual distance behind a vessel whereby seismic cables (2) are wound on winch barrels (4), and are provided with an inner cable member (3) which forms a connection with the vessel (1) during a towing operations, and is, additionally, provided with a paravane/control (14, 15) to guide and maintain the cable (2) laterally in relation to the towing vessel (1). Reliable and simple depolyment and towing of the seismic cables (2) at a large distance laterally in relation to the center line of the vessel is achieved by running the inner cable member (3) through at least one guide pulley (5) suspended from a line (7) that is adjustable in length from the vessel, and is, preferably extended over a derrick device (9) projecting from the vessel. Guide pulley (5) can be hauled in and paid out from the vessel, at the same time as inner cable member (3) can be let out to a greater length from the vessel.

Arrangement for deployment of seismic cables

An angular member provided on seismic cables towed by a vessel and laterally displaced in parallel and in relation to the course of the vessel comprises a frame at least partly enclosing the cable in the area of angular deflection between an inner cable portion extending obliquely to the towing direction and the active main cable portion. The frame is formed of two frame plates secured in spaced relationship and having at the lead-in end for the cable a cable-fastening device and at the other end a pivotable ramp swingable in the plane of the frame plates. The ramp has a further fastening device for the cable. Another fastening device is pivotably connected to the frame plates for connecting thereto a wire to a paravane or the like. When towed in the water the angular member absorbs most of the forces normally exerted on the cable at the area of angular deflection.

Angular member for seismic cables towed by a vessel

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Garnes, Norway

Jan-Age Langeland