LOGGING PLAN
The logging program is designed to measure physical properties using a suite of standard geophysical logs and hole shape using the borehole televiewer (BHTV) log. In particular, the BHTV will be used to characterize the shape and volume of the borehole in the vicinity of the strainmeter and seismometers. This will significantly improve grouting procedures for the instruments. The Formation MicroScanner (FMS) will provide a detailed resistivity image of the borehole, including fractures and conductive zones. Temperature logs will be emphasized for identification of permeable zones and inflow/outflow from both drilling-induced and natural fractures in the holes. Spontaneous potential (SP) log will provide in situ measurement of the streaming potential. SP changes are of electrochemical and electrokinetic origins and related to the active flow in permeable formations.
The RCB-cored pilot hole at both sites will be logged with the standard triple-combo tool string and the FMS/sonic/temperature tool string. The triple combo tool string includes the Natural Gamma-ray Sonde (NGS) to measure radioactivity, the Accelerator Porosity Sonde (APS), which measures porosity, the Hostile Environment Lithodensity Sonde (HLDS) to measure denisty, and the Dual Induction tool (DIT-E), to measure resisitivity. The triple combo tool string also measures the spontaneous potential and makes a caliper measurement. The FMS/sonic/temperature tool string includes the Formation MicroScanner, the dipole shear sonic imager (DSI), and the Lamont temperature tool (TLT) combination, along with a natural gamma ray tool (NGT).
Following casing operations, the open part of the instrumented borehole at both sites, which includes that portion of the hole below the 10-3/4-in casing, will be logged with the BHTV at a logging speed of ~1 m/min.
We anticipate that ~1.5 days (1.2 days for the RCB hole and 0.3 days for the instrumented hole) will be required for logging operations at Site JT-1C and 1.2 days (1.0 days for the RCB hole and 0.2 days for the instrumented hole) at Site JT-2G (Table 1).
UNDERWAY GEOPHYSICS
Standard ODP practice is to collect 3.5- and 12-kHz echo-sounder data on the approach to each site. Assuming operations at the two primary sites goes as planned, no other surveys will be conducted during Leg 186.