ABSTRACT

Four wells in the offshore Gulf of Mexico have penetrated through four different salt sheets and into underlying formations. Interpretations of sonic and density logs, together with mud weight variations, imply highly overpressured regimes below each of the four salt sheets. Models of the development with time of sediments and salt sheets are presented to show the estimates of timing and magnitude of this build-up of overpressure.

Investigations are given of both horizontal and tilted sand sheets, together with sheets having a sub-salt thief sand, to provide estimates of (a) thermal focusing by the highly conductive salt; (b) timing and magnitude of pressure build-up and bleed off in formations underlying the impermeable salt sheet; (c) porosity retention by formations below the salt.

Importance of salt sheets as an impermeable seal for hydrocarbon retention, and high porosity due to overpressure development, make the subject matter of significance to exploration assessments in the Gulf of Mexico³.