TABLE OF CONTENTS Logs have been an integral part of the formation evaluation effort of fractured media since 1951 when Mardock and Myers, and Lyttle and Ricke published techniques for evaluating the fractured Spraberry trend of Texas using radioactive and induction logs. These pioneering efforts provided reasonable results for distinguishing lithologies. However, quantitative analysis was not possible. Since then, many interpretation techniques have been developed. For completeness, this chapter discusses modern tools and interpretation techniques, but also old logs that are the only ones available in wells drilled more than 15 years ago.
These logs are frequently used in attempts to detect fractures. Pickett indicated in 1963, and it is still recognized today, that the recordings of acoustic velocity generated by a logging tool identify four wave types:
The first type is a compressional wave, which travels from transmitter to formation as a fluid pressure wave, is refracted at the well bore, travels through at the compressional wave velocity of the formation, and arrives at the receiver as a fluid pressure wave.
The second type, a shear wave, travels from transmitter to formation as a fluid pressure wave, goes through the formation at the shear wave velocity of the formation, and comes back to the receiver as a fluid pressure wave. Particle motion of a shear wave is perpendicular to the borehole axis.
A fluid or water wave, the third type, travels from transmitter to receiver at the compressional-wave velocity in the borehole fluid.
The final type is a low...
