Measuring Pore Pressure in Marine Sediments with Penetrometers: Comparison of the Piezoprobe and DVTP-P Tools in ODP Leg 204

Fugro-McClelland Marine Geosciences Inc.’s piezoprobe, a penetrationbased tool used to determine pore pressure and hydrologic properties within a borehole, was deployed for the first time in the Ocean Drilling Program (ODP) on ODP Leg 204 in July 2002. Analysis of the piezoprobe data suggests that in situ pore pressure is 9.5 MPa, which is approximately the hydrostatic pressure (9.53 MPa). The piezoprobe deployment and modeling of the results provides one of the first measurements of in situ permeability made within the borehole. From the piezoprobe dissipation data, we estimate in situ permeability of approximately 1.5 10 m for the hemipelagic clay. This is consistent with laboratory-measured permeability (~1x10 m) on hemipelagic clay samples from nearby ODP Site 892. The piezoprobe results were compared to a Davis-Villinger Temperature/Pressure Probe (DVTP-P) measurement made at the same depth, and in the same lithology, but in an adjacent borehole. The DVTPP is also a penetration-based tool, however it has a much wider probe diameter. The DVTP-P generated a higher peak pressure that did not dissipate as much as the piezoprobe pressure, which resulted in a DVTP-P estimate of in situ pressure that nearly equals the overburden stress. The results suggest that a narrow diameter probe like the piezoprobe can be used to rapidly determine in situ pressure and hydrologic properties in sites investigated by the Ocean Drilling Program. Measuring Pore Pressure in Marine Sediments with Penetrometers 181