After reaching the coring depth of 607 mbsf, Hole 1146A was filled with viscous mud, reamed, and flushed of debris. We first ran one full pass and a shorter repeat pass with the triple combo tool string, including the hostile environment natural gamma-ray sonde (HNGS), accelerator porosity sonde, hostile environment lithodensity sonde (HLDS), and dual-induction tool (DIT; resistivity) (Fig. F28). (See the "Related Leg Data" contents list.) The Lamont-Doherty temperature/acceleration/pressure tool was not run because it failed during Hole 1143A operation, and attempts to fix it were unsuccessful.
Next, we ran two full passes with the FMS, long-spaced sonic (LSS), and natural gamma-ray spectrometry tool (NGT) string (Fig. F28). Before this descent, the pipe was lowered to 242 mbsf, below an interval of swollen clays where the triple combo tool string had slight difficulty passing through. Finally, we ran three full passes with the GHMT string including the nuclear magnetic remanence sonde, susceptibility measurement sonde, and NGT (Fig. F28). The magnetic intensity recording failed in a prior run but was fixed before the two successful passes. The wireline heave compensator (WHC) performed well. Sea heave was between 0.5 and 1.5 m for the duration of the logging. Logging operations started at 1600 hr on 24 March and finished at 1235 hr on 25 March (Table T17).
All three tool strings reached within several meters of the bottom, indicating that little debris fell from the borehole wall. The two passes for the three tool string runs showed generally excellent repeatability for all the log parameters. The interval from 124 to 188 mbsf featured alternating large washouts and swollen clays. Above this depth and all the way up to 87 mbsf, the caliper saturated or nearly saturated. Below 250 mbsf, the hole was in good condition other than some fine rugosity (Fig. F29).
The HNGS data were poor in the upper interval, where caliper saturation resulted in a poor hole-size correction. The values of standard (total) gamma ray (HSGR) were consequently too low; elsewhere, the data were of good quality. The DIT was effective in the lower interval. However, in the poor-contact section of the hole, both the spherically focused log (SFL) and the medium induction phasor-processed resistivity (IMPH) read somewhat lower than the values from deep induction phasor-processed resistivity (IDPH), reflecting borehole influences (Fig. F29).
The FMS tool performed well. The first pass showed regular 0.25-m tool heave, as usual. Apparently the WHC did a better job compensating for sea heave during the second pass. The observed stick-slip of the tool string was on the order of 0.25 m. This effect on the data was corrected during the processing of the FMS images with the Geoframe software. The LSS log is of good quality for the entire hole. The two P-wave velocity measurements are almost completely superimposed (Fig. F29).
The magnetic intensity data recorded during the GHMT runs displayed the typical random spikes that were expected from this tool. Most of these spikes were on the order of 20 nT, but a few were hundreds of nT. In general, the spikes do not repeat between the two passes, so a good splice should be possible. These spikes were edited out in the data presented in this report.
In general, HSGR and computed gamma ray (HCGR) from the HNGS tool in the triple combo run read 10% to 25% higher than spectroscopy gamma ray or computed gamma ray from the NGT in the FMS-LSS run, a difference easily accounted for by eccentricity and hole-size correction. Contrary to the NGT, the HNGS corrects for borehole diameter and potassium in the borehole fluid, although the corrections near individual large washouts were apparently inadequate. The HNGS is more sensitive than the NGT; hence, its results are presented in Fig. F30 (column 1).
The downhole logging and core-sample data together suggest that below the logging depth of 87 mbsf, Hole 1146A could be divided into four main intervals of distinct physical properties. The general dividing lines seem to be at ~250, ~420, and ~520 mbsf (Fig. F29).
Above 250 mbsf the caliper frequently saturated, indicating severe hole washouts. Correspondingly, neutron porosity and bulk density values from downhole logging are spiky, and the shallow resistivity (SFL) is less than the medium (IMPH) and deep (IDPH) resistivity (Fig. F29). Gamma ray (reflecting the combined effects of potassium, thorium, and uranium) and density values from both downhole and core logging all increase from 100 to 170 mbsf and then decrease from 170 to 250 mbsf (Figs. F30, F31). The porosity profiles either remain constant or increase slightly with depth from 170 to 240 mbsf, in contrast to the typical, compaction-related decrease with depth found in sections both above and below this interval (Fig. F32).
Caliper measurements show that the hole condition in interval 2 is not only significantly better than that of interval 1 above but is also better than that of interval 3 below (Fig. F29). In this interval, several physical properties indicators increase with depth, including bulk density, electric resistivity, P-wave velocity, and gamma ray (Figs. F29, F30, F31, F32). Neutron porosity and magnetic susceptibility decrease with depth in this interval, although a change in the trend of magnetic susceptibility was observed at 385 mbsf (Fig. F29). The decrease in magnetic field with depth in this interval is likely to be caused by the influence of the drill pipe on the upper ~80 m of the log (Fig. F32).
Caliper data show slight rugosity in interval 3 (Fig. F29). Apparently the rugosity was sufficient to cause moderate spikes in bulk density, P-wave velocity, and photoelectric effect (PEF) data from downhole logging (Figs. F29, F31, F32). Relatively low values of these parameters, as well as of magnetic susceptibility, were observed at 407, 426, and 499 mbsf, where the caliper reached local maxima. Within interval 4, bulk density, resistivity, P-wave velocity, and gamma ray all increase with depth, whereas porosity decreases slightly with depth (Figs. F29, F30, F31, F32). Magnetic susceptibility remains constant for most of interval 3 but decreases from 510 to 520 mbsf.
This interval has an excellent hole condition as revealed by a smooth caliper curve (Fig. F29). Within this interval, several parameters increase with depth, including bulk density, P-wave velocity, and gamma ray (Figs. F29, F30, F31, F32). Magnetic susceptibility, PEF, and magnetic field remain nearly constant for the interval, whereas porosity decreases slightly with depth.
The trends in gamma ray from the NGT and HNGS tool strings agree well despite some constant offsets (Fig. F30). The trend in magnetic susceptibility from downhole logging is also in good agreement with that from MST measurements (Fig. F31). The trends of thorium and PEF agree above 200 and below 50 mbsf but are opposite between 200 and 520 mbsf (Fig. F31). CaCO3 measurements of core samples and PEF from downhole logging show similar trends, especially above 200 mbsf and between 280 and 460 mbsf (Fig. F31). Natural gamma rays from downhole logging and MST measurements agree in their general trends as well (Fig. F32).
Bulk density from downhole logging agrees with that from both MAD measurements of core samples and core logging, although the downhole logging data show considerably greater spikes above 220 mbsf and between 440 and 500 mbsf (most likely because of poor hole contact where washouts are severe [Fig. F31]). Porosity calculated from downhole bulk density is ~10%-15% less than that calculated from the moisture content of core samples in intervals 2 and 4. The logging porosity is very spiky in intervals 1 and 3, presumably also a result of poor hole condition (Fig. F32). Finally, P-wave velocity from core-sample measurements is ~0.3 km/s smaller than that from downhole logging at 280-420 mbsf. The discrepancy between these two types of measurement decreases gradually to 0.1 km/s at 580 mbsf (Fig. F32). The FMS data showed alternating layers of relatively high and low conductive layers (Fig. F33).