Temperature Logging - Cased-Hole Log Analysis and Reservoir Performance Monitoring - page 115

the temperature taken at one point and comparing it to the temperature taken at
some other point, such as 1 ft deeper, or shallower, depending on the direction of
logging. Differentiation can be on a depth or on a time basis. Provided that the log-
ging speed remains constant, both methods produce the same answer. Figure 8.13
shows a conventional temperature survey together with a differential-temperature
curve. Note that where even slight changes in temperature occur the differential
curve accentuates the occurrence. Where the temperature does not change with
depth, the differential curve is likewise unchanged.
Fig. 8.13 Differential-temperature log. Courtesy Baker Hughes