Fluid flow in sedimentary basins: a geologist’s perspective

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Abstract
Summary: Water begins to flow from higher-energy to lower-energy positions as soon as sediment begins to accumulate in a new sedimentary basin, and flow continues during the sedimentary development of the basin. Water expelled by compaction from the compactible less-permeable beds displaces water in the less-compactible more-permeable beds. Compaction flow also causes subsidence that contributes to the sedimentary development of a basin.The pattern of flow is determined by the stratigraphy. In transgressive sequences, it is downwards in mudstone to the basal permeable unit and then lateral towards the land of the time. In regressive sequences, it is upwards and downwards in mudstones towards the intercalated sandstones and then lateral in these towards the land. In compacting sequences of alternating sandstones and mudstones, the sandstones drain distinct isolated hydraulic units that are related to the stratigraphy.When a sedimentary basin ceases to accumulate sediment and compaction has reached equilibrium, the flow patterns change and the main energy comes from elevation of the intake areas.In rift basins the main source of compaction water is the thick mudstone in the post-unconformity-disconformity sequence. Abnormal pressures in the pre-unconformity-disconformity sequence indicate lack of flow in this part of the basin.