A statistical study of the geological limits to Advanced Piston Coring: ODP Legs 101-149

Abstract

The Advanced Piston Corer (APC), a soft sediment coring system developed from the hydraulic piston corer (HPC), allows recovery of ocean sediments with minimal coring disturbance. As a coring too[, the APC system is subject to limitations imposed by the effect of geology, for example the physical properties and sediment type. Critical questions to be addressed here are the inability to thrust the core barrel into a stiff sediment formation and the need to extract it without suffering mechanical failure. These two problems, penetration and overpull refusal, are the major reasons for stopping APC coring. Measurements of physical properties have been made on more than 400 APC holes cored from beneath the ocean floor. These samples represent several sediment types deposited in various environmental settings, as well they consist of different physical properties (bulk density, etc.). The properties measured at the limits of APC coring (deepest APC core) are used to understand how APC coring works as a function of sediment type and of the physical properties of the sediment. This understanding may allow the APC to be used more efficiently in the future and improve the quality of science obtained from APC cores. Based on the data from the Ocean Drilling Program (158 APC holes), this study indicates trends in the physical properties of sediment recovered from deepest APC core with the depth of maximum APC penetration from each hole. The performance of the APC varies with lithology. The occurrence of APC refusal (overpull and penetration refusal) depends on different physical properties and sediment types. In general, overpull refusal occurred mostly in biogenic sediments, while non-biogenic sediments with higher wet-bulk density and lower water content or porosity are more likely to lead to penetration refusal than others. The introduction of APC-129 (the upgrade of the APC), which was first used during ODP Leg 130 in 1990, improved the performance of APC coring in calcareous sediments. A pullout force is needed to withdraw the core barrel from the sediment by raising the drill string. The results of APC coring accord with the theoretical relationship between pullout forces and shear strength. Pullout force correlated with shear strength of the sediment and the depth below seafloor.