Abstract

Many velocity surveys have been shot in which the actual depth of the well phone was in question at one or more of the levels shot in the borehole. The computed time to the questioned level would not fit the other data obtained from the velocity survey, i.e., the data from the questioned level would not fit the time-depth curve within reason or, more recently, it could not properly be fitted to the corrected continuous velocity log data. If the “first break” of the questioned level could not be repicked to conform to the other data, a notation was made in the velocity survey report that the depth of the well phone was probably in error. Although this assumption was correct in many cases, there are various other reasons why data from one check level should not fit the rest of the data.

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