| Fluid flow in a compacting/aggrading sedimentary basin can be considered as occurring in three separate but interacting hydrogeologic regimes: meteoric, compactional, and thermobaric/metamorphic. In the meteoric regime, water moves away from recharge areas in response to the force of gravity. In the compactional flow regime, fluids move in response to excess fluid pressures created primarily by compaction disequilibrium. The thermobaric/metamorphic regime occurs in that portion of the basin where pressures and temperatures are sufficient for metamorphic reactions to release fluids, the importance of this regime to the hydrodynamics of the overlying sediments is not known.;Large scale mass and energy transfer are apparently required for diagenesis, petroleum migration, and ore formation. Forced convection (advection) in either the meteoric or compactional regimes has generally been considered to be the dominant process of enhanced energy and mass transfer. Analyses indicate that free convection may be important on a local scale in thick sands or on a regional scale in sand-shale sequences.;A two-dimensional cross-section finite-element model has been developed to simulate the evolution of the compactional and meteoric flow sytems as a sedimentary basin undergoes the processes of sedimentation, sediment compaction, and basinal subsidence. The model is applied to the northwestern Gulf of Mexico sedimentary basin.;The results of the model demonstrate that the evolution of the meteoric and compactional flow systems is extremely dependent on the permeability and especially on the lateral permeability and continuity of highly permeable units. Changing the permeability in a relatively small area on the marginward edge of the basin can have a great impact on the overpressures in the entire basin. Penetration of meteoric fluids is dependent on the permeability of the basin and may be influenced by the presence of growth fault zones in the compactional regime. Permeable units within the compactional regime are not overpressured until the next major loading event, may repressurize with new loading events, and drain adjoining lower permeability units. A lag time occurs between loading events and maximum flux rates due to the presence of low hydraulic conductivity materials. Compactional fluxes are probably insufficient to account for diagenesis, unless considerable focusing of flow occurs. |
