Unformatted text preview: s don’t want to keep the amplitude of filter constant This type of filters is used for special processing. • Phase filter: In some cases, instead of filtering out frequencies, it may be necessary to adjust the phase of data. Ex: Survey in coastal area, the survey runs in land & marine together. On land, the field crew will use velocity geophones & in lagoon they will use a Pressure hydrophone. Where geophones & hydrophones are used together, the traces were recorded by geophones will be out of phase with those recorded by hydrophones. Its necessary to phase shift the traces of hydrophones before stacking We apply Phase filter to change the phase of all frequencies without altering amplitude. • Shaping filter: It is a filter by which the analysts can alter both the phase & frequency content of seismic trace. • Inverse filter: It is any type of filters which reverse the effects of filter has already been applied to data 40 Geology & Geophysics in Oil Exploration Mahmoud Sroor Geology & Geophysics in Oil Exploration Static correction: It is often called statics, a bulk shift of a seismic trace in time during seismic processing. A common static correction is the weathering correction, which compensates for a layer of low seismic velocity material near the surface of the Earth. Other corrections compensate for differences in topography and differences in the elevations of sources and receivers. 1-Elevation method For each station, there is an elevation is measured. This difference in elevation causes the horizontal reflector appears as curved. So this method is used to shift all of data up or down to datum level (Sea level for example). 2-Uphole method: This method is used to estimate the thickness & velocity of weathered layer. This method involves drilling a hole into the weathering layer (up to 300ft) An uphole geophone placed near the hole & a seismic source (usually charges of dynamite) are set in the hole The geophone records seismic waves at each depth. These depths &...
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- Spring '10
- Geology, Volcano, Tephra, Volcanic Ash, Geology & Geophysics, Mahmoud Ahmed Sroor