3-D Seismic Acquisition, Processing and Display
As mentioned at the beginning of the last chapter, the interpretation phase of a seismic project is considered by many to begin at the survey design phase. It is during this phase that the acquisition parameters are planned, and these can have a significant impact on what size of subsurface body can be imaged, how well they will be imaged and so on. These same considerations apply to the collection of 3-D seismic data as well.
To understand the need for 3-D seismic acquisition geometries, we need to go back to looking at how 2-D seismic data are acquired. It will be recalled (Chapter 3) that for most 2-D work the sources and receivers are spread out in a line. Reflections are assumed to come from the piane through the earth that corresponds to that line. In reality however, the acoustic energy from the shot expands out spherically (i.e., in 3 dimensions) from the source location. As such, reflected energy can be received from features (e.g., faults, reefs, channels) that are located outside of the piane of the section. These reflections, sometimes referred to as “sideswipe”, will be recorded and show up in the 2-D seismic data. Since the true subsurface stratigraphy and structure are generally unknown, the features can be mistakenly thought to He in the piane of the seismic section. In fact, the interpreter may have no way of telling where the reflections come from, even if he/she cari recognize the features as sideswipe. The result