Inversion of up and down going signal for ocean bottom data

Seismic Acquisition of Ocean Bottom Data

Although conventional streamers acquisition is well developed in terms of technology and processing techniques, it has significant limitations. For example, in obstructed oil fields, working with streamers could be difficult. In addition, streamers are more prone to drift and to be affected by weather conditon, which may compromise repeatability in time-lapse reservoir monitoring (4D). These limitations bring out a growing demand for ocean bottom seismometers (OBS). OBS data acquisition is an alternate approach in which seismometers are placed at the ocean bottom and shots are fired at the ocean surface.

OBS data acquisition can be done with either ocean bottom cables (OBC) or with nodes (OBN). Because the OBS method uses geophones and hydrophones, it can measure both compressional and shear waves. This capability permits separating up- and down-going waves at the seabed and therefore provides good opportunities for imaging with multiples.

Multi-component streamers (Pharez et al., 2008) also permit separation of up-going and down-going waves, but because the data are recorded near the sea surface, imaging with multiples is much more limited than with OBS in deep water.

To understand the events represented by the up-going an down-going signals, consider Figure 2. For ocean bottom data acquisition, down-going events include direct arrival, receiver ghosts, and higher-order pegleg multiples. On the other hand, up-going events include primaries, and pegleg multiples. Since the kinematics of these events are quite distinct for up-going and down-going signals, an inverse problem can be formulated to fit the up and down signals jointly. Before formulating the inverse problem, we will dicuss methods for separating receiver signals into their up- and down-going parts.

Fig2
Figure 2. Left: The down-going signal consists of events such as direct arrival, receiver ghosts, and higher-order pegleg multiples. Right: The up-going signal consists of events such as primaries and other pegleg multiples. [NR]

Inversion of up and down going signal for ocean bottom data