BAKER HUGHES - Drilling Fluids Reference Manual

PRESSURE PREDICTION AND CONTROL
porosity decreases because a denser material transmits sound waves at a higher velocity than a
less dense material. Porosity generally decreases at a near linear rate as a function of depth in
normally near a straight line with gradual reduction in travel time as a function of depth.
Increased shale porosity (which usually indicates a change in compaction and abnormal
pressures) would produce an increase in shale travel time. Figure 12-6 is a plot of shale transit
time versus depth. Note the normal compaction trend indicating normal formation pressures
down to approximately 11,000 feet. Below this depth, shale travel time values begin to increase
in relation to extrapolated normal compaction line, indicating abnormal formation pressures.
Figure 12 - 6 Shale Transit Time vs. Depth
BAKER HUGHES DRILLING FLUIDS
REFERENCE MANUAL
REVISION 2006 12-8