Previous Talks

Wednesday, January 14th, 2009

Exploring shallow overpressure in the Ursa Basin, Gulf of Mexico, through in-situ measurements, lab experiments, and basin modeling

Peter B. Flemings, Jackson School of Geosciences, U.T. Austin

Abstract

In 2005, the Integrated Ocean Drilling Program (IODP) Expedition 308 drilled three research wells across the Ursa Basin, deep water Gulf of Mexico, to illuminate overpressure and fluid flow near the mudline. We measured pressure using a pore pressure penetrometer, took extensive core, and performed extensive logging. We find pore pressures reach 70 % of the hydrostatic effective stress (lambda* =0.7) in the first 200 meters below sea floor (mbsf). We conducted extensive uniaxial consolidation tests on core samples to obtain consolidation and flow properties. We find that the compression index linearly decreases with in situ void ratio and we use this relationship to successfully predict pore pressure from porosity. Finally we use laboratory measurements of compressibility and permeability to parameterize a two dimensional basin model. Our results show that the observed pressure field is accurately produced given the observed sedimentation rates of 3 to 12 mm/yr. In these models, flow is driven laterally along the Blue Unit from locations where overburden is thick toward locations where it is thin: submarine landslides and shallow water drilling problems are encountered where flow is focused toward these thin overburden locations.

Speaker Biography

Peter Flemings is a Professor with the Jackson School of Geosciences, U.T. Austin. He received his B.A. degree from Dartmouth College, and both an M.S. degree and Ph.D. in geology from Cornell University. He previously taught at Penn State, was an associate research scientist at Lamont-Doherty Earth Observatory of Columbia University and the Crosby Distinguished Lecturer at the Massachusetts Institute of Technology. He leads the U.T. GeoFluids Consortium and his research focuses on the study of pressure, stress, and fluid migration in sedimentary basins. (http://www.ig.utexas.edu/people/staff/flemings/)