The Determination of Sound Velocity in Core Samples

Citation

Urick, Robert Joseph (1939) The Determination of Sound Velocity in Core Samples. Master's thesis, California Institute of Technology. doi:10.7907/CYS4-WB36. https://resolver.caltech.edu/CaltechTHESIS:02262010-114009583

Abstract

In an area that is being explored for the first time with the reflection seismograph, the manner in which the longitudinal wave velocity varies with depth---the so-called "velocity distribution"---is unknown. Structural features can be located without a knowledge of this function, but they cannot be measured. In the present advanced state of reflection seismology more than mere detection of structural detail is necessary. And in order to compute dips and depths from the reflections and thereby obtain a quantitative structural picture, the velocity distribution has to be known with a tolerably decent degree of accuracy.

There are in common use at present two methods of velocity distribution determination. The more direct of these consists simply of lowering a seismometer to successively different depths down a well already drilled, shooting at the surface near the casing head, and observing the travel times of the first impeti from the records. This method is simple, direct, and without doubt gives the best possible determination of velocity distribution. It necessitates, however, a well that is available for use in this way, as well as the expense of running a seismograph crew for a day or two. The second method of velocity measurement involves only surface shooting and recording. Travel time differences for different shooting distances are carefully measured from surface records of several hundred reflections, plotted, and an average velocity computed. This method involves a great amount of computing and inconveniences resulting from the fact that considerable shooting has to be done in an area before the velocity distribution becomes to be known.

Some sort of inexpensive laboratory measurement of velocity would apparently, therefore, be of value. Important wildcat wells of major companies are now being more or less continuously cored. If the sound velocity in representative samples of the corings at different depths could be measured some idea of the velocity-depth function might be obtained. It is the purpose of this thesis to examine the correlation, if any, between the velocity distribution as obtained in the customary manner as described above, and that obtained from laboratory measurement of velocity in core samples from a well in the same area.

Thesis Files