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doi:10.2204/iodp.proc.347.108.2015 Downhole measurementsLogging operationsHole M0064A was drilled to 41.5 m drilling depth below seafloor (DSF). In preparation for logging, the hole was circulated with seawater and the drill string was pulled back in the hole to 2 m wireline log depth below seafloor (WSF). Logging operations started in Hole M0064A with rigging up of the Weatherford logging setup. Before the running in the hole of the first tool string could be started, a problem with the winch was noticed. After the problem was fixed, the gamma ray tool (MCG)/array induction tool (MAI) tool string, measuring total gamma ray and induction, could be run in the hole, and a downlog was started. The seafloor was picked up by the gamma ray, and the tool string came out of the pipe. Immediately, a sudden drop in tension indicated that the tool string set up at ~5 m WSF. Logging operations were abandoned in this hole after this unsuccessful attempt. During rig-up of the logging setup, the pipe was completely out of the hole, probably causing the top of the hole to collapse. Downhole logging measurements in Hole M0064D were performed after completion of coring to a total depth of 41.2 m DSF. In preparation for logging, the hole was circulated with seawater and the pipe was pulled back to ~7.6 m WSF. For downhole logging in Hole M0064D, two tool strings were deployed:
The MCG/MAI tool string was lowered and downlogged to 31 m WSF. The hole was then uplogged to the seafloor. The wireline depth to the seafloor was determined from the step increase in gamma ray values. After this, the MCG/SGS tool string was lowered and reached 26.4 m WSF while downlogging. The hole was then uplogged to the seafloor. The tools provided continuous and good quality log data. Logging unitsHole M0064D is divided into three units on the basis of the logs (Fig. F17). The uplog was used as the reference to establish the wireline log depth below seafloor depth scale. Logging Unit 1: base of drill pipe to14.7 m WSFNatural gamma ray in this logging unit generally increases with depth, with some fluctuations around 10 and 13 m WSF. The negative excursions that occur in this logging unit may correspond to the beds of silty sand described in lithostratigraphic Unit III (see “Lithostratigraphy”). At 14.7 m WSF is a sudden drop in NGR values. Resistivity slightly increases from 9 to 13 m WSF and then decreases to its lowest value at 15 m WSF. Logging Unit 2: 14.7–21 m WSFAfter the drop in NGR at 15 m WSF, natural gamma ray remains constant in logging Unit 2, with a slight increase at the bottom of the unit. Thorium values are higher in logging Unit 2 than in logging Unit 1, with large fluctuations around 20 m WSF. Resistivity increases with depth in logging Unit 2 because of compaction. Logging Unit 3: 21–31 m WSFDeeper than 21 m WSF, the resistivity log shows constant values. The natural gamma ray log shows a slight decrease but a different trend for the different tool strings used. Total gamma ray measured with the MCG/MAI tool string is ~20 gAPI lower than the one measured with the MCG/SGS tool string. This may be due to changing borehole conditions. |
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