Page 228 - Standard Handbook Petroleum Natural Gas Engineering VOLUME2

Formation Evaluation 197

1. Those from the casing which appear as straight, parallel light and dark
bonds intermittently broken by small V-shaped spikes which indicate the
position of casing collars.
2. Those from the formation which appear as wavy, irregular, and intermittent
light and dark bands which represent curve attenuation in the rock sur-
rounding the borehole.

Interpretation. Interpretation of CBGVDL logs involves recognition of basic
curve pattern for determining whether casing is properly bonded or not. These
curve patterns are presented in Figures 5-120 to 5-123. Four basic types of
patterns are apparent:

1. Those that show strong casing arrivals only.
2. Those that show strong casing and formation arrivals.
3. Those that show weak casing arrivals and strong formation arrivals.
4. Those that show both weak casing and weak formation arrivals.
Strong casing arrivals are shown in Figure 5-120 and are characterized by the
pronounced casing arrival pattern (straight, alternating light and dark bands).
No formation arrivals are present and cement-bond log-amplitude is moderate

Figure 5-120. CBL-VDL log run in free pipe [220].