Instrumented pressure testing chamber for characterizing sediment cores recovered at in situ hydrostatic pressure

Abstract

Marine sediments retrieved with pressure coring systems such as those used by the Integrated Ocean Drilling Program maintain samples at in situ hydrostatic pressure throughout recovery. Such pressure cores are particularly important for the study of gas hydrate-bearing sediments, which must be maintained within the gas hydrate stability field during shipboard core characterization. Until now, there has been no device capable of directly measuring a suite of physical properties on sediments contained in pressure cores without first depressurizing them. This study describes the design, construction, and deployment of the Instrumented Pressure Testing Chamber (IPTC), which was first used to measure the physical properties of pressure cores recovered ∼1530 m below the sea surface during 2005 drilling in the Gulf of Mexico. The IPTC permits drilling through the plastic liner while the core is under pressure and the sequential measurement of P- and S-wave velocities, undrained strength, and electrical conductivity. Preliminary results indicate that the seismic velocities measured on a pressure core with the IPTC are more representative of in situ seismic velocities at comparable depths than are velocities measured on conventional cores from these same depths. The flexibility of the IPTC design allows future modifications to account for restoration of effective, not just hydrostatic, stress; the addition of new types of measurements; sampling of pore fluids and sediments under pressure; and use of the device as a laboratory reactor for gas hydrates studies.