Page 133 - Acquisition and Processing of Marine Seismic Data

124 2. MARINE SEISMIC DATA ACQUISITION

FIG. 2.77 Comparison of two 3D seismic datasets with (A) 13.3 m 26 m and (B) 12.5 m 12.5 m bin sizes. After Chopra, S.,
2004. Expert answers. Theatr. Rec. 29, 1–20.

source array, and processedat13.3 m 26 mbin For denser line spacing, crossline mapping of
size. The data in Fig. 2.77B, however, was col- the structures can be more reliably achieved.
lected with eight streamers of 100 m separation In 2D surveys, line ties with vintage data as well
and dual source arrays, and processed as a nearby well are also important.
at 12.5m 12.5 m bin size. Although some of In 3D acquisition, however, the study area is
the acquisition and processing parameters are fully covered with a line interval of one-half the
different, the resolution difference between the crossline width of the whole spread. For
sections due to the different bin sizes is instance, a 400-m sail line interval is required
significant. for 8 streamer acquisition with 100 m streamer
separation. It is critically important to cover
2.5.1.8 Line Interval and Infill the whole target zone within the survey area
Separation between the sail lines is com- by evenly distributed bin fold and source-
monly determined by considering the lateral receiver offset without any data gaps in 3D sur-
resolution required for mapping the subsurface veys. In some cases, high feathering angles of the
structures in a lateral direction in 2D surveys. streamers exceeding 10 degrees due to the
However, it is a function of the number of strong ocean currents and data gaps caused by
streamers and streamer separation in 3D case. bad weather conditions, marine traffic and tech-
In 2D surveys, seismic profiles are several kilo- nical down times induce local gaps or irregular
meters apart depending on the requirements fold distribution in the 3D seismic datasets.
and purpose of the survey. For a regional 2D Streamer feathering becomes a serious issue in
seismic acquisition for reconnaissance purposes, the case of the ocean currents that change direc-
the line interval is typically not less than 5 km. tion within the 3D survey area, which causes