A compaction trend for Cretaceous and Tertiary shales on the Norwegian shelf based on sonic transit times

Grain densities measured on 74 samples from three wells and the corresponding bulk densities from the density log allowed the porosities of the samples to be determined. These values were used to establish a new relationship between transit time and porosity for Cretaceous and Tertiary shales on the Norwegian Shelf. Normally pressured and compacted Cretaceous and Tertiary shale intervals in 29 carefully selected wells were then identified and shale porosities calculated using the established shale transit time-porosity relationship. Based on these calculated shale porosities, exponential and linear depth-porosity trends are possible.