YU, Z., University of South Carolina, Columbia, SC; * J. J. O'BRIEN, South Dakota State University, Brookings, SD; and IAN LERCHE, University of South Carolina, Columbia, SC

ABSTRACT: Overpressure Build-Up in Formations Underlying Salt Sheets in the Gulf of Mexico

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

Investigations of horizontal and tilted salt sheets, together with sheets having a sub-salt thief sand, are presented to provide estimates of (a) thermal focusing; (b) timing and magnitude of pressure build-up and bleed off; (c) porosity retention.

The results suggest the likelihood of high potential for hydrocarbon trapping below salt sheets, but high drilling risk due to the expected overpressure.

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 Mexico.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.