Seismic applications

Today, most surveys are three-dimensional (3-D) designs where source and receiver points are distributed on a region of the earth's surface. This distribution typically forms a grid pattern, composed of source lines and receiver lines. When source and receiver lines are orthogonal, the 3-D survey design is called an orthogonal design. Design considerations for an orthogonal design include the spacing of the source and receiver lines, and the spacing of the source and receiver locations along the lines. The signal sent from any given source point is monitored by multiple receivers on different lines. The set of receivers that monitor a single source signal are often referred to as the template or active spread.
The classical approach to seismic processing can be summarized in two main steps. The first step includes pre-processing of the data and the application of static corrections. The purpose of pre-processing is to extract reflected waves from individual shots, by filtering out the parasitic events created by direct and refracted arrivals, surface waves, converted waves, multiples and noise. It is intended to improve resolution, compensate for amplitude losses related to propagation, and harmonize records by taking into account source efficiency variations and eventual disparities between receivers. Static corrections, that are specific to land seismic acquisition, are intended to compensate for the effects of the weathering zone (Wz) and topography. Records are then sorted in common mid-point gathers or constant offset sections.
If the data are sorted in common mid-point gathers, the second processing step is the conversion of the seismic data into a migrated seismic section after stack. This second step includes the determination of the velocity model, with the use of velocity analyses, the application of normal move-out (NMO) corrections, stacking and migration. If dip values are sufficiently large, velocity analyses provide time-depth relationships that are affected by dips. To overcome this inconvenience, a correction for dip effects or dip move-out (DMO) correction prior to determining velocity relationships must be applied to the data. If the data are sorted in constant offset sections, a pre-stack time (PSTM) or depth (PSDM) migration procedure which simultaneously performs dip correction, NMO correction, common mid-point stack and migration after stack, is applied. It is indispensable to have a good velocity model to carry out the migration process. The role of migration is to place events in their proper location and increase lateral resolution, in particular by collapsing diffraction hyperbolas at their apex.

We present applications of the signal processing tools in seismic processing:

Processing of a shot point.
Dispersion analysis of Rayleigh waves.
Love Waves.
Refraction-Reflection seismic survey.
Seismic processing with an industrial software.
3D seismic example.
VSP processing.
Marine vibrator.

Recordings of land seismic data obtained during acquisitions are composed of body waves (refracted, reflected, diffracted, converted) and surface waves. Surface waves, which amplitude decreases rapidly with depth, are confined near the surface. These surface waves, made up of pseudo-Raleigh waves and Love waves, are harmful to the quality of seismic reflection ; but in certain specific studies, the analysis of their dispersion allows evaluating the evolution of shear waves' velocity according to depth and determining the shear modulus in the first meters of the substratum. In marine environment, in a configuration low bottom (less than 200 meters), for a range of low frequencies (between 2 and 200 Hz) and on large distances, the propagation of sismo-acoustic waves is done on several wave guides. These guided waves are dispersive waves. The analysis of their dispersion allows establishing a model of the propagation environment. The analysis and filtering of dispersive waves can be achieved on one-component or multi-components devices. We present some tools used in signal processing for the analysis and filtering of dispersive waves. We illustrate the application of these processing methods on several examples of guided waves observed during acquisitions of seismic data onshore or offshore. For each example, we describe the processing methods which have been applied and geophysical information which could be extracted.

We present 6 field examples:

Multi component OBS
Dispersion analysis with OBS data
Rayleigh waves: f-k filtering
Rayleigh waves: dispersion analysis
Rayleigh waves: SVD filtering
Rayleigh waves: SMF filtering