BAKER HUGHES - Drilling Fluids Reference Manual

PRESSURE PREDICTION AND CONTROL
Pressure
Gradient
in Equivalent
Fluid Weight
(lb m /gal)
10.0
10.5
11.0
11.5
12.0
12.5
13.0
13.5
14.0
14.5
15.0
15.5
16.0
17.0
17.5
MIOCENE-
OLIGOCENE
South Louisiana
1.09
1.15
1.20
1.28
1.34
1.43
1.53
1.65
1.78
1.93
2.10
2.33
2.60
3.58
5.00
Ratio: Observed Conductivity / Normal Conductivity
Or: Normal Resistivity / Observed Resistivity
FRIO
FORMATION
S. Texas Gulf Coast
1.34
1.55
1.78
1.97
2.18
2.43
2.68
2.96
3.33
3.60
3.95
4.31
4.67
5.72
WIL COX
FORMATION
S. Texas Gulf Coast NORTH SEA
.08
.13
1.22
1.28
1.39
1.50
1.64
1.80
2.00
2.21
2.44
2.71
3.03
4.0
1.50
1.76
1.95
2.30
2.60
2.90
3.25
3.60
3.85
4.2
SOUTH
CHINA SEA
1.32
1.50
1.65
1.80
2.00
2.20
2.45
2.65
2.85
3.1
4.5 3.30
3.54
3.70
NOTE: Plot conductivity values for shale on 3-cycle semi-log paper.
Table 12 - 1 Predicted Pressure Gradients vs. Conductivity or Resistivity Ratios
Example
Figure 12-4 shows an example of an IES log. From the plot in Figure 12-5, it can be easily seen
that a marked trend of normal pressure zone is obtained until a depth of approximately 11,000
feet. At this point, the sharp change indicates that an abnormal pressure zone has been
encountered. Figure 12-5 shows the conductivity plot versus depth for the log in Figure 12-4.
Sample calculations from Figure 12-5:
• For abnormal pressure zone at 13,000 feet,
• Shale conductivity observed = 1670
• Shale conductivity normal = 630
Calculate the ratio of observed conductivity to normal conductivity:
If the formation were of Miocene-Oligocene geologic age, Table 12-1 indicates a formation
pressure equivalent to approximately 16.1 lb m /gal drilling fluid density.
Sonic Logs
Sonic log data is used in a manner similar to the conductivity method of pressure prediction.
Sonic logs measure transit time of sound for fixed distance through formations (the same as the
seismic information). Interval transit time (microseconds per foot) decreases as formation
BAKER HUGHES DRILLING FLUIDS
REFERENCE MANUAL
REVISION 2006 12-7