A comprehensive geotechnical site investigation program comprising in situ piezocone penetration tests (PCPT) and extensive onshore static and dynamic laboratory testing scope were performed for integrated soil characterization of the first offshore methane hydrate (MH) production test area off the coasts of Atsumi and Shima Peninsulas, offshore Japan.
The in-situ and laboratory geotechnical test results along with a suite of geophysical data (subbottom profiler data (SBP), 3D seismic and Logging-while-Drilling (LWD) data) have been utilized to assess soil condition and develop pertinent design parameters for offshore foundation design at the production test sites under static and dynamic loading conditions.
Results of the integration and interpretation of geotechnical and geophysical data are presented and discussed here. Soil characteristics and geotechnical parameters developed for the soils encountered at the production test sites, including soil index properties, vertical stress histories, static and dynamic shear strength properties, strain rate effect, small-strain shear modulus Gmax, thermal conductivity, hydraulic conductivity and coefficient of consolidation and permeability are provided in detail.
Relevant geotechnical properties for soils at typical Gulf of Mexico (GOM) deepwater sites are also presented in the paper for reference purpose. It is noted that the deepwater cohesive sediments in offshore Japan are relatively stiffer, experiencing greater undisturbed undrained shear strength values and higher over consolidation ratio (OCR) than those encountered in Gulf of Mexico (GOM) sites at similar depths.
