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Section 1: Fluid Flow in Compacting Basins |
Faculty of Earth Sciences, King Abdulaziz University, Jeddah, Saudi Arabia
Fluid pressure in excess of hydrostatic pressure can be generated during sediment loading. The rate of increase in the excess fluid pressure (psi Ma–1) can be calculated from the sedimentation rate (ft Ma–1) of a formation and its average bulk density. Further, the inferred directions of horizontal migration of the compaction fluid can be shown by means of a contour map based on the rate of increase in the excess fluid pressure, the first derivative of which gives the intensity of the horizontal motion of the compaction fluid (psi Ma–1 mile–1). The horizontal fluid movement may be essential for driving hydrocarbons towards a trapping position during the primary stages of migration.
Application of this technique using the regional isopach maps of the Jurassic, Cretaceous and Tertiary formations in the Arabian Gulf region suggests that the major oil fields are concentrated in areas of relatively strong horizontal fluid movement. The area N of the Qatar Peninsula, where horizontal migration of fluid was relatively weak during the Cretaceous period when both the Jurassic and Cretaceous source rocks reached their early stages of oil generation, seems to have relatively low concentrations of oil. At present there are relatively few oil fields in this part of the region.
