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doi:10.2204/iodp.proc.336.106.2012 APCT-3 temperature measurementsDownhole temperature measurements were attempted with the APCT-3 in Hole U1382B on Cores 336-U1382B-3H through 5H at 24.5, 34, and 43.5 mbsf, respectively. The measurements were suspended for deeper cores because of poor recovery, which we suspected was caused by the extra time the core was left in the formation in order to provide sufficient data to extrapolate to in situ temperatures. However, the cores contained coarse sand–sized to pebble-sized rock fragments, which might also have caused the poor core recovery. Unfortunately, the temperature data quality for the three attempts was poor, owing to motion of the coring shoe in weak, shallow sediments that apparently also contributed to poor recovery. The raw temperature-time records for the three attempts (Fig. F28) show evidence of motion of the corer during the measurement period, with indications for multiple disturbances involving mixing of fluids from above or multiple penetrations of the probe in the formation beneath the bit. As a result, none of the data fit well to the numerical model (TP-Fit) that represents the ideal decay of the frictional heating pulse on penetration of the coring shoe, and large errors are associated with all attempts to use this model to extrapolate to apparent in situ temperatures. The results seem to be consistent with in situ temperatures of 3°–3.6°C at all three measurement points, but the large error ranges in the fits provide no confidence that the measurements actually resolve an in situ temperature gradient with any accuracy. |
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