Temperature Data Processing
IODP-USIO logging contractor: LDEO-BRG
Location: Cascadia Margin (NE Pacific)
Latitude: 48° 38.7006' N
Longitude: 126° 59.0069' W
Logging date: October 22-23, 2005
Sea floor depth (drillers'): 2206.2 mbrf
Sea floor depth (loggers'): 2205 mbrf
Total penetration: 304.3 mbsf
Total core recovered: 62.49 m (54.1 % of cored section)
Oldest sediment cored: Presumably Pleistocene – no diatoms found in the lower part of the hole
Lithologies: Clay and silty clay, with some sandy intervals
Temperature Tool Used: LDEO-TAP
Depth versus time recording available: YES
Logging string 1: DSI/SGT/TAP
The TAP tool acquires borehole temperature, tool acceleration, and hydrostatic pressure. It may be run in either memory mode, where the tool is fastened to the bottom of logging string and data is stored in the on-board memory, or in telemetry mode, where the tool is run alone and data is recorded in real-time by the third-party data acquisition system. When the tool is run in memory mode, the stored data is dumped to the third party data acquisition system upon the tool's return to the rig floor.
Borehole fluid temperature is recorded with one thermistor located at the bottom of the tool. The internal temperature of the tool is recorded as well. A pressure transducer is included to turn the tool on and off at specified depths when used in memory mode. Typically, data acquisition is programmed to begin 100 m above the seafloor. A 3-axis accelerometer is also included to measure tool movement down hole. These data are expected to be instrumental in analyzing the effects of heave on a deployed tool string which will lead to the fine tuning of the WHC (wireline heave compensator).
Drilling and circulation operations considerably disturb the temperature distribution inside the borehole, thus preventing equilibrated temperature conditions. The amount of time elapsed between the end of drilling fluid circulation and the beginning of logging operations is not long enough to allow the borehole to recover thermally.
During this leg depth versus time data was recorded on a personal computer (part of the LDEO digital logging data acquisition system in the ODP Downhole Measurements Laboratory aboard the JOIDES Resolution), with input from the Schlumberger MAXIS computer. The depths recorded through this system correspond to the wireline cable length measured by Schlumberger during the recording of the logging data. These depth data were merged with the data recorded in memory by the Temperature-Acceleration-Pressure Tool (TAP) by matching absolute time in the two data sets. The depths in the processed files are reported in meters below sea floor (mbsf). At each hole, the constant depth shift applied to the original temperature logs was the same as that applied to all of the other logs; it is given in meters below rig floor in the header of the processed file.
Information about the temperature logging operations can be found in the Site Chapter, ODP Initial Reports Expedition 311.
For further information about the processing, please contact:
E-mail: Cristina Broglia
E-mail: Gilles Guerin