Lateral transfer: a source of additional overpressure?

Overpressure generated by disequilibrium compaction can be enhanced at structural crests by the lateral transfer of fluids from deep, overpressured parts of a basin along laterally extensive inclined aquifers. Fluid flow modelling shows that the effect of an inclined aquifer ranges from being minimal to being a significant contributor (>10 MPa) to crestal pore pressures depending on the style of structural evolution, the burial rate and the aquifer relief. Dynamic fluid flow models show that the Centroid Concept, a method for estimating crestal pressures based on a static view of subsurface fluid pressures, does not in general predict the pressure distribution associated with a dipping aquifer. A case study is presented from the Central North Sea where the Pre-Cretaceous reservoir forms part of an aquifer with 2.5 km of relief from the structural crest to the low point. The inclined aquifer is covered by a ubiquitous low permeability layer and has undergone extremely rapid recent burial (> 500 m/ Ma). As expected from the generic modelling analysis, this combination of factors means that lateral transfer has a minor effect on the pressure development in the case study. (C) 2000 Elsevier Science Ltd. All right's reserved.