Downhole logging was conducted in Hole 1172D after it had been drilled to a depth of 766.5 mbsf with a 9.785-in drill bit. The hole had been cored between 343.6-372.4 mbsf and 497.4-766.5 mbsf. The remaining sections of the hole had been drilled ahead with a center bit (see "Operations"). After a wiper trip (see "Downhole Measurements" in the "Site 1168" chapter) and displacing the hole with sepiolite mud, the RCB bit was released and the pipe was set at 160 mbsf in preparation for logging. The pipe was raised by 10 m during the first tool-string run only (Fig. F37). Three tool-string runs were planned; the triple combo, the GHMT-sonic, and the FMS. However, operational difficulties resulted in measurements only being taken with the first two tool strings. Details of the logging operations are shown in Figure F37.
The heave was heavy throughout logging operations, routinely exceeding 6 m and reaching a maximum of 10 m. The wireline heave compensator (WHC) stroked out on six occasions during the main run of the triple combo, resulting in ~40% of the data being collected without heave compensation. After returning the triple combo to the rig floor, it was discovered that the caliper on the hostile-environment lithodensity sonde had sustained minor damage to the caliper wear plate.
While logging with the GHMT-sonic, the WHC stroked out continually, resulting in all of the data being collected without heave compensation. A decision was made to rig up and run in with the FMS and assess heave conditions again before opening the pads on this tool. The WHC was turned on when the tool was going down through the open formation, but it stroked out almost immediately. When attempting to restart the WHC, a serious oil leak from the cylinder end assembly was discovered and, bearing in mind the time constraints and the weather conditions, a decision was made to cancel any further logging.
The principal results are shown in Figures F38, F39, F40. The hole conditions were variable, with a particularly rugose borehole between ~165 and 200 mbsf, ~415 and 500 mbsf, and ~685 and 695 mbsf. The main cause of error in the data, however, will be the lack of heave compensation, which will make it very difficult to determine accurate depths for each set of measurements. This will be a particular problem for core/log integration and cyclostratigraphic analysis.
There is generally good agreement between log density and core density values, with both data sets showing stepwise variations downhole (Fig. F41). Core porosities are similar to the log values down to ~400 mbsf (Fig. F42), but below this there is a relatively large disparity in the two data sets until the very bottom of the hole (>700 mbsf). Core P-wave velocity measurements are considerably lower and more variable than the log values between 150 and 300 mbsf (Fig. F43), but below this depth there is relatively good agreement between the data.
Preliminary comparisons between the log data and the core lithology (see "Lithostratigraphy") show that major fluctuations in the logs are often correlative with distinct changes in the sediments. Some examples are given below: