Wednesday, February 11, 2015

Instantaneous Velocity

Instantaneous velocity is the speed at a given moment of a wavefront in the direction of energy propagation (Sherrif, 1984) . It is also used to refer to velocities that are derived from sonic or acoustic logs obtained in a borehole, since these are typically taken every few centimeters in the borehole.
In its simplest form, a sonic tool consists of a tranmsitter that emits a sound pulse and at least two receivers at some distance from the transmitter.
The sound propagates from the transmitter through the mud , the formation and through the mud again to the receivers where it is detected as a pressure pulse.
Sonic tools are designed such that sound travels slower through them than through most formations.

The difference in arrival times at two receivers , divided by the distance separating these receivers , provides a measurement of the interval transit time, delta t , or slowness . The velocity of the formation is the inverse of the slowness.

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