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Geology _ Geophysics in Oil Exploration

We repeat these steps with all wells to get the true

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Unformatted text preview: rth. • Pseudo Average Velocity: when we have time from seismic & depth from well • True Average Velocity: when we measure velocity by VSP, Sonic, or Coring • Interval Velocity: The velocity, typically P-wave velocity, of a specific layer or layers of rock, • Pseudo Interval Velocity: when we have time from seismic & depth from well • True Average Velocity: when we measure velocity by VSP, Cheak shot • Stacking Velocity: The distance-time relationship determined from analysis of normal moveout (NMO) measurements from common depth point gathers of seismic data. The stacking velocity is used to correct the arrival times of events in the traces for their varying offsets prior to summing, or stacking, the traces to improve the signal-tonoise ratio of the data. • RMS Velocity: is root mean square velocity & equivalent to stacking velocity but increased by 10% • Instantaneous Velocity: Most accurate velocity (comes from sonic tools) & can be measured at every feet • Migration Velocity: used to migrate certain point to another (usually > or < of stacking velocity by 5-15%) 42 Geology & Geophysics in Oil Exploration Mahmoud Sroor Geology & Geophysics in Oil Exploration Migration: A step in seismic processing in which reflections in seismic data are moved to their correct locations in the x-y-time space of seismic data, including two-way travel time and position relative to shot points. Migration improves seismic interpretation and mapping because the locations of geological structures, especially faults, are more accurate in migrated seismic data. It attends to deal with diffractions & dipping interfaces. Types of Migration: • Time Migration: A migration technique for processing seismic data in areas where lateral velocity changes are not too severe, but structures are complex. Time migration has the effect of moving dipping events on a surface seismic line from apparent locations to their true locations in time. • Depth Migration: A step in s...
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