92 Seismic Imaging 3D surveys has become a fundamental step to ensure that the 3D data quality meets structural, stratigraphical and lithological requirements. Pre-planning includes the evaluation of both geophysical and non-geophysical parameters such as environmental considerations, health and safety requirements, etc. Specific pre-planning tools (Cordsen A., Galbraith M., Peirce J., 2000) have been developed to estimate all acquisition characteristics such as offset, fold and azimuth distributions, effects of surface obstacles, etc. Pre-planning steps aim to define the geological targets of the 3D survey, with the associated geophysical parameters, design and costs. Figure 4.1 2D and 3D seismic imaging (after J. Meunier, 2004, IFP School course). In 2D acquisition, the image obtained after processing is a vertical seismic section. The horizontal axis of the section represents the geographical abscissa of subsurface points along the acquisition profile, and the vertical axis represents the record time. The seismic events that appear on the records correspond to the arrivals of waves reflected at normal incidence on the seismic horizons. The seismic horizons correspond to discontinuities of acoustic impedance; their picks provide a structural image of the subsurface. 3D seismic acquisition provides full volume interpretation, consisting of a collection of sections parallel to each other. Surface seismic has vertical and horizontal resolutions measured in tens of meters with lateral investigation distances only limited by the size of the area investigated by the seismic surveys. This chapter is neither a basic introduction nor a theoretical study of seismic acquisition and processing; its goal is to show, through the use of field examples, the contribution of seismic reflection to near-surface imaging, and to hydrogeological
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