Page 60 - Acquisition and Processing of Marine Seismic Data

2.1 COMPONENTS OF MARINE SEISMIC ACQUISITION 51

resolution, enhancing the amplitude spectrum. the pressure fields are used to decompose the
A much higher-resolution data termed broad- seismic wave field into the upgoing and down-
band seismic data can be obtained by assem- going pressure and velocity wave fields (Carlson
bling extra sensors into the towed streamers in et al., 2007). The ultimate goal is to eliminate the
addition to the conventional pressure hydro- effect of ghost reflections to obtain broadband
phones to cancel the ghost signal. In the last seismic data, and using multiple sensor mea-
decade, multisensor towing streamer technol- surements, the approach is quite simple: The
ogy has been under development. Currently, upgoing pressure and velocity wave fields are
there are three types of multisensor recording of the same polarity. Since the downgoing pres-
systems on the market: sure field, the ghost signal, is reflected from the
sea surface (Fig. 2.11A), its polarity is reversed in
• GeoStreamer (PGS)
the hydrophone output, whereas it has the same
• Sentinel MS (Sercel)
polarity as the upgoing velocity wave field in the
• IsoMetrix (Schlumberger)
particle velocity sensor (Fig. 2.11B). After a care-
These systems record pressure data using a ful processing, much higher resolution data con-
hydrophone and one or two additional acceler- sisted of only the upgoing pressure field with a
ation components for both crossline and vertical relatively wider spectrum is obtained if the mea-
wave fronts to obtain the measurement of full surements of pressure and velocity wave fields
upgoing and downgoing seismic wave field. are summed up (Fig. 2.11C). Fig. 2.12 shows data
The result with a 3D deghosting is an enhanced examples for pressure and velocity sensors and
broadband subsurface image used for high res- their amplitude spectra.
olution mapping and reservoir monitoring. This Following the success of the GeoStreamer,
technology was actually developed by PGS in similar multi component solid streamers have
2007 when they introduced their first multisen- been developed in recent years. Sentinel MS is
sor solid streamer with hydrophones and a radially symmetrical three-component (3C)
motion sensors, called GeoStreamer, which uses solid streamer with a strength member at the
a dual-component technology to measure both core. It contains a hydrophone to measure the
pressure and vertical component of the particle pressure field, and two orthogonally mounted
velocity simultaneously (Tenghamn et al., 2007). analog accelerometers to directionally measure
The particle velocity measurements along with the crossline and vertical wave fronts, as well

FIG. 2.11 (A) Up- and downgoing signal ray paths measured by the pressure (hydrophone) and velocity sensors, (B) cor-
responding schematic measurements for upgoing (U) and ghost (G) signals, and (C) comparison of amplitude spectra from
pressure and velocity fields as well as the final upgoing pressure field.