Publication Name: The North West Shelf Australia
Authors: E.L. Horstman
Date Published: July 1988
Number of Pages: 20
Reference Type: Book Section
Abstract:
Empirically, oil and gas production on the North West Shelf of Australia is related to the presence ofoverpressured section. In turn overpressure can be related to hydrocarbon generation.
Comparison of the depth of the oil window and the top of the overpressured section and total organic carbon establishes (1) wells in which no overpressures are present because of a lack of a good pressure seal, (2) wells in which the first occurrence of overpressures is below the top of the oil window and is coincident with the top of source rock, (3) wells in which the first occurrence of overpressure is coincident with the top of the oil window and ( 4) wells in which the first occurrence of overpressure is above the oil window in a thermally immature section.
Overpressures in cases (2) and (3) are caused by hydrocarbon generation. Pressures in case ( 4) are more likely related to undercompaction of the shales, caused by inability of contained water to escape because shale
permeability seals formed early.
Hydrocarbons have been generated in the deeper overpressured areas and exploration in and adjacent to
the overpressured areas carries a lower risk than exploration in normally pressured areas.