Temperature Logging - Cased-Hole Log Analysis and Reservoir Performance Monitoring - page 106

Bottomhole Temperature Extrapolation

If t k is the circulation time and ∆ t is the time since circulation stopped, then a plot
of the observed temperature at time ∆ t against ( t k + ∆ t )/∆ t on a log scale should give
a straight line with an intercept at ( t k + ∆ t )/∆ t = 1 which will indicate the undisturbed
formation temperature, T i . Figure 8.4 illustrates the method. A worked example is
shown below. Table 8.1 lists time and temperature data recoded on sequential log-
ging runs in the same hole. The well was drilled to a depth of 7,646 ft and drilling
stopped at 22:00 on the 2nd. Circulation stopped at 02:30 on the 3rd giving a circu-
lation time of 4½ h. Analysis of this data is shown on the plot in Fig. 8.4 that indi-
cates an undisturbed formation temperature close to 116 °F.

Table 8.1 Time and temperature data

Thermometer
depth (ft)

Time off
bottom

Time since circulation
stopped (h) Logging run Temperature °F

1 7,608 07:36/3rd 5:06 99

2 7,608 12:48/3rd 10:18 106

3 7,620 14:29/3rd 14:29 107

4 7,620 20:37/3rd 18:07 110

Question # 8.1
Depth: 16,200 ft.
Drilling stopped: 00:30 h.
Circulation stopped: 04:00 h.
Circulation time: 3.5 h.

Three log runs were made, the corresponding times and temperatures were:

Tool Time off bottom Time since circulation stopped Temp. (°F)

Induction 12:15 8:15 241

Density 15:00 11:00 257

Dipmeter 17:30 13:30 262

Plot temperature vs. ( t k + ∆ t )/∆ t and deduced static formation temperature.