抄録
Overburden pressure is supported by both fluid pressure and mechanical stress at grain contacts. If the fluids in mudstones are easily expelled, compaction occurs normally, and a normal or hydrostatic pressure environment exists. The "normal compaction trend" appears on a log as a continuously decreasing mudstone porosity with depth.
Abnormally high pressure is caused during compaction by the reduction in the ability of formation fluids to flow out. This can be seen as a retardation of the formation compaction process. The abnormal pressures appear in the plot of a mudstone parameter vs. depth as positive deviations from the "normal compaction trend", or as increases in porosity. Consequently, detecting of abnormally high porosity in mudstones can aid to find high pressure zones in the subsurface.
The subsurface fluid pressure profiles in this paper are determined by using the Sonic logs which were run in Nagaoka Plain, Japan. This study can help us to understand the directions of fluid movement or hydrocarbon migration in this plain.
