Temperature Data Processing


ODP logging contractor: LDEO-BRG

Hole: 927C

Leg: 154

Location: Ceara Rise (tropical NW Atlantic)

Latitude: 27.781.' N

Latitude: 44° 28.837' W

Logging date: March, 1994

Bottom felt: 3328 mbrf

Total penetration:  358 mbsf

Total core recovered: 262.85 m (98.6 %)


Water Depth: 3319 mbrf

Temperature Tool Used: LDEO-TLT

Depth versus time recording available: NO


Logging Runs


Logging string 1: DIT/SDT/HLDT/NGT

The wireline heave compensator was used to counter the mild ship heave. The WHC was turned off at 105 mbsf during the DIT/SDT/HLDT/NGT run.



Tool Information


The LDEO-TLT tool is a self-contained, high precision, low-temperature logging tool that is attached to the bottom of the Schlumberger tool strings. The tool provides two temperature measurements (in degree Celsius, recorded by a fast-response and a slow-response thermistor.  The fast-response thermistor, though low in accuracy, is able to detect sudden, small temperature excursions caused by fluid flow between the formation and the borehole. The highly accurate, slow-response thermistor can be used to estimate heat flow. Pressure and the two temperature measurements are recorded as a function of time: conversion to depth can be based on the pressure reading (Legs 123-157) or, preferably, on simultaneous recording (by Schlumberger) of depth and time (Legs 159-181).


Data Processing


The pressure data has been initially smoothed using a 50-point running average prior to the depth calculation. A linear relationship of pressure versus depth has been calculated from the pressure reading at the mudline and the maximum logged depth. The pressure at the mudline corresponds to the pressure recorded by the tool during the calibration stop (about 5 minutes), which takes place at the mudline on each logging run.


Depth = 355 * (Pressure - 343)/(386 - 343)




Depth = mbsf

Pressure = bars

386 bars = maximum pressure recorded

343 bars = pressure at mudline

355 mbsf = maximum logged depth


The temperature data has been smoothed with a 10-point running average.

This procedure does not fully account for the vagaries of the pressure readings that result in lots of ups and downs in the generated depth channel. Further problems arise because of pumping during logging operations, which affects the pressure, especially when the Side Entry Sub is used. Also, whenever heavy pills of mud are used, the pressure-depth calculation is affected, resulting in a non-linear effect that is difficult to account for. If the pressure conversion coefficient is recalculated for the mudline, the resultant total depth is often wrong.



Information about the temperature logging operations can be found in the Site Chapter (Operations, Downhole Measurements, and Heat Flow sections), ODP IR volume 154.

For further information about the processing, please contact:


Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia