Geology _ Geophysics in Oil Exploration

The stacking velocity is used to correct the arrival

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Unformatted text preview: e samples back again to its original place, we use Demultiplex technique. Gain Recovery: It is a step in seismic processing to compensate for attenuation of the amplitude of data. As shot fired, Waves spread as a cone in 3 dimensions. This spreading of energy is called Spherical divergence. This spreading of energy from source point causes the energy to decrease with increasing depth. High frequencies are more rapidly to absorb than low frequencies by the rock. So, seismic energy reflect from deep geological event will be received at geophone as weak signal, & near surface will be received as strong signal. We use the Gain Recovery to enhance these weak signals True amplitude: means the real amplitude on seismic trace without any gain applied. Equalization Scaling (Trace scaling): It is known also as Normalization. It is used because after all seismic traces is stacked, strong amplitude will carry more weight than weak ones, So we run this step to scale up weak traces & scale down strong traces (normalize the trace with itself). Automatic Gain Control & Balance: AGC & Balance are used to build up weak signals (differ from Trace scaling that they are based on smaller time analysis window where Trace scaling applies gain at large time window). Balance divides trace into several windows which may overlap & AGC uses a sliding window instead of set of windows 38 Geology & Geophysics in Oil Exploration Mahmoud Sroor Geology & Geophysics in Oil Exploration Editing: Step is used to remove bad traces, noisy channels or open channels. Muting: Zero out arrivals that are not primary P-wave reflections. Deconvolution: A step in seismic signal processing to recover high frequencies, attenuate multiples, equalize amplitudes, produce a zero-phase wavelet or for other purposes that generally affect the wave shape. Let’s consider a simple case as shown in figure. In ideal case, Geophone still stationary until the first reflection arrived, then it makes one movement & return to its stationary position again so the ideal seismogram reflections shows a series of spikes. In real case, Seismogram for these layers would be pre...
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