Cement Bond Logging - Cased-Hole Log Analysis and Reservoir Performance Monitoring - page 195

Tools Available

In general conventional CBL, tools are available as either through-tubing versions
(for workover jobs) which have a 1-11/16

″ or 2-1/8 ″ diameter or as full-diameter

tools for primary completions with a 3-5/8 OD. Apart from these classifi cations,

based on the physical dimensions, CBL tools are also available as the more modern
ultrasonic scanning type. Both will be discussed.
Figure 12.6 illustrates a conventional CBL tool. It consists of an acoustic trans-
mitter and two receivers. In actual practice, the tool may be identical with an open-
hole sonic tool but with only one transmitter and two receivers being used. The near
receiver is placed 3 ft from the transmitter and is used for amplitude measurements.
The far receiver is placed 5 ft from the transmitter and is used for wave-train
recordings.

″

Fig. 12.6 Conventional CBL
tool. After Schlumberger

Operating Principles

Three paths are available for a compressional wave emanating from the transmitter:

1. Through the casing
2. Through the formation
3. Through the borehole fl uid

Typical travel times for these three media are 56 ʼ s/ft for casing, 60-100 ʼ s/ft for

the formation, and 170-200 s/ft for the borehole fl uid. The shortest time path for

the acoustic energy to travel is through the casing and the longest is through the

ʼ