OTC 21569--'CPT Stinger' - An Innovative Method to Obtain CPT Data for Integrated Geoscience Studies

摘要

A new deepwater static cone penetrometer system, “CPT Stinger”, was used to investigate subsurface conditions at a number of production sites in the deepwater Gulf of Mexico. Same site high-resolution geophysical data and long cores obtained with a Jumbo Piston Core (JPC) system illustrate the excellent correlation obtained with continuous geotechnical and geophysical data for defining the spatial variation in soil properties. The high cost of drilling deepwater borings and sampling at widely spaced intervals imposes a significant constraint on obtaining a sufficient quantity of high quality soils data. Thus, improved methods are desirable for more quickly assessing requisite soil properties without sacrificing accuracy. The “CPT Stinger” system is a new tool that can fill this role. This new system allows the same general suite of JPC coring equipment to be modified for CPT testing and can be deployed from an oilfield supply vessel. By simply replacing the standard piston core liner with a CPT system containing thrusting rods, a power/control module, and CPT data logging system, the field operation can quickly be converted from sampling to in situ testing mode. The results show that the new system provides continuous soundings with centimeter-depth accuracy and stratigraphic consistency. In addition to the acquisition of high-quality static CPT data, the sampling rate of the CPT logger allows the acquisition of dynamic CPT data during free fall that can be adjusted for velocity differences to emulate static data A particularly effective way to use the system is in conjunction with nearby, continuous sampling with JPC cores and subbottom seismic profiles. This allows the correlation of the CPT results with strengths from continuous samples over a significant depth of overlap and with the geophysical cross sections. Correlations are presented in the paper for undrained shear strength data from long cores with insitu CPT data. Following the premise that more information acquired for a given budget tends to reduce the risks associated with foundation design and installation planning, the economic benefits of rapidly acquiring the geotechnical data from a lower cost vessel are also discussed.