Cement Bond Logging - Cased-Hole Log Analysis and Reservoir Performance Monitoring - page 193

Fig. 12.3 Compressive strength vs. attenuation rate for various cements. Reprinted with permis-
sion of the SPE from Pardue et al. © 1963
The data for Fig. 12.3 refers to steel pipes completely surrounded by cement. In
the case of partial cementation, it is of interest to note the data of Fig. 12.4 where
the percentage of the pipe's circumference is plotted against the attenuation rate.
This relationship is linear (i.e., the smaller the percentage of the circumference
cemented, the less the attenuation rate). It is also worth noting that at least a ¾-in.
thickness of cement is required in order for these relationships to hold. Figure 12.5
shows that after a thickness of ¾ in. is exceeded, attenuation rate is constant. Thus,
measurement of the attenuation rate of a compressional wave propagated along the
casing gives information regarding the bonding of the cement to the casing.
Information regarding the bonding of the cement to the formation has to come from
a separate source such as a wave-train recording which can be viewed as a variable-
density display (VDL). In order to understand this more fully the tools used must be
studied.