Abstract
If fluid in mudstone is easily expelled, compaction occurs normally, and a normal or hydrostatic pressure environment exists. The “normal (compaction) trend” appears on the Induction or Sonic log as a continuously decreasing mudstone porosity with depth.
On the other hand, if escape of fluid is inhibited, compaction may not occur sufficiently and a high porosity- high fluid pressure situation will result. The abnormal pressures appear in the plot of a mudstone conductivity or transit time vs depth as possitive deviations from the “normal trend”, or as increases in mudstone porosity. Consequently, detecting of abnormal high porosity in mudstones by such logs as the Induction and Sonic can aid to find high pressure zones in the subsurface.
