Abstract
Fluid pressure gradients in shales can be determined by the porosity distributios of the incompletly compacted shales. It is possibel, therefore, to estimate permeability changes in shales by using the fluid pressure gradient (derived from the shale porosity distribution) and Darcy's law. The integration of these permeability changes with porosity values in shales can be used to establish a relation between shale porosity and permeability in the subsurface.
This method of analysis applied to Cretaceous shales in Alberta and Saskatchewan, Canada, revealed that the decrase of shale permeability with decrease in porosity is less than that given by the Archie's relation, which is based on sandstone and carbonate rocks. This new knowledge ofthe porosity-permeability relation in shales promotes a better understanding og fluid movements in the shales during compaction, which will influence the migration and accumulation of hydrocarbons.
