Petrophysical investigations on sediment core CRP-2A from the Ross Sea, Antarctica

A suite of petropysical measurements - velocity versus pressure, bulk density, porosity, matrix density, and magnetic susceptibility -was undertaken on 63 core plugs from CRP-2A. These data are used to calibrate neutron, resistivity, and magnetic susceptibility well logs. Agreement between core-plug magnetic susceptibility measurements and both well-log and whole-core data is excellent. Comparison of core-plug bulk densities with continious well-log density records shows very good agreement. Core-plug measurements of matrix density permit conversion of the well-log and whole-core density records to porosity. Sands and muds exhibit similar downhole compaction patterns, and both patterns are consistent with 250 ± 150 m of exhumation. Pervasive cementation, particularly in the lower half of the core, has affected many CRP-2A petrophysical parameters:
(1) fractional porosities are reduced by about 0.05 - 0.10 in the lower part of the hole;
(2) velocity and porosity rebound are much smaller than is usually observed for unconsolidated sediments with burial depths similar to CRP-2A;
(3) velocities are unusually insensitive to pressure, suggesting that any exhumation-induced microcracks have been scaled subsequently;
(4) the velocity/porosity relationship lacks the characteristic signature of exhumation-induced microcracks;
(5) the velocity/porosity relationship changes with depth, indicating downhole increase in consolidation;
(6) Vp/Vs ratios of the highest-porosity sediments are unusually low, implying enhancement of framework stiffness.