Page 63 - Acquisition and Processing of Marine Seismic Data

54 2. MARINE SEISMIC DATA ACQUISITION

FIG. 2.13 Common marine seismic energy sources. (A) GeoMarine 6000-J sparker array, (B) water gun (Sercel), (C) GI gun
(Sercel), (D) sleeve gun (Seamap), (E) G gun (Sercel), and (F) LL gun (Teledyne Bolt).

and gas industry. The volume of each air gun (Fig. 2.13B), and the seismic signal is generated
3
typically ranges from 10 to 250 in and total during the collapse of this bubble. Water gun
gun volume within an air gun array varies from source signatures need a signature deconvolu-
3
1000 to 8000 in for a modern 2D or 3D seismic tion process since it has pressure variations,
vessel. For most air gun types available in the termed precursors, due to the initial acceleration
market, it is also possible to create different size of the water from the gun chamber appearing
volume chambers during the operation using before the main pressure signal is formed, which
dedicated plastic volume reducers for a better makes the source signal of the water gun a
array tuning. A detailed explanation of the air mixed-phase wavelet (Lee et al., 2000). The main
gun source signals and signatures, gun arrays advantage of the water guns is that they do not
and their performance parameters, etc., is given have bubble oscillations since they do not dis-
in Section 2.2. charge air, and therefore, there is no need to per-
The basic operation of a water gun is similar form an array tuning to suppress the bubble
to that of the air gun, but a shuttle is used to dis- noise. They can generate relatively high frequen-
charge the water, instead of compressed air, into cies, and hence are suitable for high-resolution
the water column to produce a vacuum bubble surveys while their low-frequency components