Seismic velocity converter
Convert seismic velocity between m/s, ft/s and the slowness a sonic log records.
That's about the same as sandstone. A reflector one kilometer down would return in about 666.7 ms.
What it means
How fast does sound travel?
Rock velocity rises with depth, compaction and cementation, so a single figure describes one interval rather than a whole well.
Every unit
Your velocity in every unit
Learn
Three things worth knowing
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µs/ft = 304,800 ÷ velocity
A 3,000 m/s sandstone logs at 102 µs/ft. Slower rock means a bigger slowness, which is why the log curve runs backwards from the velocity.
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Time, then depth
Seismic sections are drawn in two-way travel time, not depth, because the velocity is not yet known. Converting them is a whole discipline of its own.
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Interval is not average
The velocity of one layer is not the average down to it. Using the wrong one puts a reflector hundreds of meters from where it really is.
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Popular velocity conversions
Background
About seismic velocity
A seismic survey measures time; turning that into depth needs velocity. Sound crosses water at 1,500 m/s, sandstone at about 3,000 and granite at 6,000.
Sonic logs record the reciprocal — slowness, in microseconds per foot — because the tool measures a delay over a fixed spacing.