Characterizing the Geomechanical Properties Beneath the Seafloor in the Terrebonne Basin, Gulf of Mexico Outer Continental Shelf

Abstract

This study characterizes the compressive behavior of sediment near the seafloor in the Terrebonne Basin, Gulf of Mexico, based on cores collected during the UT-GOM2-2 Expedition (Walker Ridge 313, Site H). The sampled section of the sediment consists of mud and carbonate ooze extending to a depth of 832 mbsf. The primary focus is on the upper 150 mbsf, a zone often overlooked during offshore drilling. Index testing included measurements of moisture content, bulk and grain density, Atterberg limits, and particle size distribution. The sediment is classed as a high plasticity silty clay. Samples from both lithologies were tested to assess compression and permeability with depth. Constant rate of strain tests were used to define primary compression and permeability behavior, while incremental oedometer tests were performed to evaluate secondary compression rates. Porosity measurements were compared to logging-while-drilling data, with significant offsets in the porosity profile with depth attributed to lithological differences. The ooze layers are found to be much more compressible than the mud layers. A unique aspect of this study is the comparison between intact and resedimented specimens during constant rate of strain testing.