Temperature Data
Processing
IODP logging
contractor: USIO/LDEO
Hole: 1256D, re-entry
Expedition:
Location: Guatemala Basin (NE equatorial Pacific)
Latitude: 6° 44.1631' N
Longitude: 91° 56.6012' W
Logging date:
Sea floor
depth (driller's):
3645 m DRF
Sea floor
depth (logger's):
3643.5 m WRF (from previous expeditions)
Total
penetration: 5165 m DRF (1520 m DSF)
Total core
recovered: not applicable (mostly cored during previous expeditions))
Oldest sediment recovered: Calcareous nannofossil ooze (Middle Miocene) at Hole 1256B during ODP Leg 206
Lithologies: Clay-rich sediments and nannofossil ooze (sediments). Basalt and gabbro (basement).
In 2005 the Borehole Research Group of the Lamont Doherty Earth Observatory designed a temperature tool that could acquire data in combination with a Schlumberger tool string or as a stand-alone tool in memory mode. Schlumberger designed and provided the telemetry interface hardware. The tool measures borehole temperature and axial acceleration of the tool string, as well as power supply and reference voltages and internal temperature.
The MTT succeesfully recoded data during a downlog and uplog run. For most measurements (resistivity, GR, sonic etc.) the uplog is the reference log, because we have a much better control over speed, depth and motion while pulling the tool up.
Temperature is the one measurement where the downlog is more accurate, because the temperature sensor is at the bottom of the tool string and the temperature in the water column is less disturbed by the tool motion than on the way up (when you pull the tool, the temperature sensor comes after the ~30m-long tool string, which has stirred the water column in the borehole). However, these considerations are mostly relevant when you try to get an equilibrium temperature profile, which you can get only when reentering a hole that has been left undisturbed for months or years. During IODP Expedition 335, the temperature log occurred after extensive cleaning operations at the bottom of the hole, and both temperature measurements recorded downhole and uphole are far from the formation temperature. On the way down, the recording stopped when the bottom of the tool string was at 5100 mWRF (~1457 mWSF) to calibrate the resistivity tool while going down to the bottom of the hole. Because of the way data are written and of the tool string configuration, the last data recorded by the MTT were at ~1429 mWSF. This has to do with the lengths of the various tools and the way the data are transmitted between tools. This, however, was not a big concern because the borehole temperatures were far from the equilibrium temperature and at the very bottom of the hole the difference between the uplog and downlog is generally minor. In short, the uplog could provide the missing data.
The temperature data acquired with the MTT have been depth-shifted and depth-matched during the processing of the standard log data. For a complete account, refer to the Standard Data Processing Notes.
Additional information about the drilling and logging operations can be found in the Operations and Downhole Measurements sections of the expedition report, Proceedings of the Integrated Drilling Program, Expedition 335. For further questions about the logs, please contact:
Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia
Tanzhuo Liu
Phone: 845-365-8630
Fax: 845-365-3182
E-mail: Tanzhuo Liu