Calculating Porosity
Many relationships between travel time and porosity have been proposed, the most commonly accepted is the Wyllie time-average equation. The equation basically holds that the total travel time recorded on the log is the sum of the time the sonic wave spends travelling the solid part of the rock, called the rock matrix and the time spent travelling through the fluids in the pores. This equation is empirical and makes no allowance for the structure of the rock matrix or the connectivity of the pore spaces so extra corrections can often be added to it. The Wyllie time-average equation is:
where = seismic velocity of the formation; = seismic velocity of the pore fluid; = seismic velocity of the rock matrix; = porosity.
Read more about this topic: Sonic Logging
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