Temperature Data Processing
ODP logging
contractor: LDEO-BRG
Hole: 905A
Leg: 150
Location: New Jersey Offshore (NW Atlantic)
Latitude: 38° 36.828' N
Longitude: 72° 17.024' W
Logging date: July, 1993
Bottom felt: 2709 mbrf (used for depth shift to sea floor)
Total penetration: 740.1 mbsf
Total core recovered: 834.8 m (93.7%)
Water Depth: 2698 mbsl
Temperature
Tool Used: LDEO-TLT
Depth versus time recording available: NO
Logging
Runs
Logging string 1: DIT/DSI/NGT
Logging string 2: HLDT/CNTG/NGT
The wireline heave compensator was used during both runs.
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).
DIT/DSI/NGT Run. The pressure data has been initially smoothed using a 300-point running average prior to the depth calculation. Depth was calculated by a linear relationship defined 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 = 650 * (Pressure - 255)/(338.4 - 255)
where
Depth = mbsf
Pressure = bars
338.4 bars = maximum pressure recorded
255 bars = pressure at mudline
650 mbsf = maximum logged depth
Temperature data was smoothed using a 20-point running average. Despite the smoothing, the procedure described above does not fully account for the vagaries of the pressure readings that may 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.
HLDT/CNTG/NGT Run. The pressure data has been initially smoothed using a 50-point running average prior to the depth calculation. Depth was calculated by a linear relationship defined 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 = 583 * (Pressure - 278)/(354 - 278)
where
Depth = mbsf
Pressure = bars
354 bars = maximum pressure recorded
278 bars = pressure at mudline
583 mbsf = maximum logged depth
Information about the temperature logging operations can be found in the Site Chapter (Operations, Downhole Measurements, and Heat Flow sections), ODP IR volume 150.
For further information about the processing, please contact:
Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia