in]) to more than 42 cm at 135 mbsf, where the caliper arm was fully extended
(Fig. F50). The
tool was then lowered again but still could not go below 165 mbsf.Only one logging run was attempted in Hole 1108B. The pipe was raised to 100 mbsf and a triple combo string with the dual induction tool (DIT) (Table T7, Fig. F15, both in the "Explanatory Notes" chapter) was lowered downhole. The mudline depth determined by the drill pipe (drill-pipe depth) was at 3188.3 mbrf (3177 mbsl).
The count recorded downward from 2979 mbrf identified the mudline wireline depth at 3188 mbrf, and this value was used to convert mbrf to mbsf (Fig. F49). The logging string was stopped for 3 min at mudline to provide a depth reference for the TLT log. Upon reaching open hole at 115 mbsf, the tool string encountered some resistance causing cable tension to drop by ~5 kN (1000 lb). This was finally overcome after working the tool string up and down. The tool string then reached 165 mbsf, where the same problem arose again. Despite numerous attempts, the tool string did not go deeper.
The log was then run from
165 to 125 mbsf at 550 m/hr mainly to acquire caliper data and investigate
borehole size. The accelerator porosity sonde (APS) minitron source was not
activated so that subsequent passes could record NGR. This first pass revealed a
very rough hole with diameters varying from drill-bit size (25.1 cm [9
in]) to more than 42 cm at 135 mbsf, where the caliper arm was fully extended
(Fig. F50). The
tool was then lowered again but still could not go below 165 mbsf.
A second logging pass was then recorded up from 163 mbsf at 525 m/hr with the APS source activated. This pass was stopped at 120 mbsf, which is below the upper level of downgoing resistance, and the tool brought down again to record a slower, third upgoing pass.
The third pass was run from 163 mbsf at 225 m/hr to record high-resolution (5-cm vertical sampling) APS data up to the base of the pipe. This pass continued to acquire NGR inside the pipe up to the mudline where the tool string was again stopped for 2 min, 45 s to provide a second TLT depth reference. The tool was then brought up to 3150 mbrf, where it was stopped again for calibration before being pulled out of the hole.
The caliper data from the three passes are consistent (Fig. F50) and suggest that the downward progression of the tool may have been hampered by the difficulty of finding a normal-size hole when passing through the bottom of a large washout area.
The NGR readings from the third pass are distorted between 160 and 110 mbsf by the formation activation by the APS during the second pass (Fig. F50). As a result, there is a gap in the usable NGR between 110 and 120 mbsf, because this interval was logged only during pass 3 where the formation was still strongly influenced by the former pass APS activation (Fig. F51).
The APS data (Fig. F51) show very high porosities, which are above the highest values of comparable physical properties measurements from core. This is typical in clayey formations but may also be caused by hole size and roughness.
The low resistivity values seem consistent with the inferred high porosity.
The TLT was set to start recording temperature at 200 m above the seafloor and kept on recording until the return to the drill floor (Fig. F52). The depth shift applied to its data to obtain mbsf is 3186.7 m. The highest recorded temperature was 16°C, which corresponds to the deepest point of the log at 165 mbsf (Fig. F53). Circulation is typically maintained as the hole is being prepared for logging. It is then stopped when the logging strings are rigged up. This helps explain the warming observed in the borehole during logging. Further time-dependent analysis is included in the temperature measurements section. The warmer water temperature encountered while running in pipe when coming out the hole (Fig. F52) may be related to water upwelling caused by the tool movement.
