TEMPERATURE DATA PROCESSING
ODP logging
contractor: LDEO-BRG
Hole: 904A
Leg: 150
Location: New Jersey Offshore (NW Atlantic Ocean)
Latitude: 38° 61.806' N
Longitude: 72° 46.084' W
Logging date: July, 1993
Bottom felt: 134 mbrf (used for depth shift to sea floor)
Total penetration: 567.7 mbsf
Total core recovered: 557.5 m (96.7 %)
Water Depth: 1123 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
Logging string 2: FMS/GPIT/NGT
The wireline heave compensator was used during the second and third run. Seas were calm.
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 100-point running average prior to the depth calculation. Depth was calculated by two methods: For downhole data 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 = 578 * (Pressure - 97)/(158 - 97)
where
Depth = mbsf
Pressure = bars
158 bars = maximum pressure recorded
97 bars = pressure at mudline
578 mbsf = maximum logged depth
For uphole data, the depth has been calculated from the uniform logging speed (235 m/hr = 0.0653 m/s) that was maintained during the entire pass.
Depth = 578 - 0.0653 * (Time - 4630)
Where
Time = sec
578 mbsf = maximum logged depth
Uplog and downlog temperature data was smoothed with a 20-sample running average.
HLDT/CNTG/NGT Run. Both the fast thermistor and the pressure transducer did not function during this run. A calculation of a temperature profile versus depth has been attempted for the uplog only. Depth has been calculated by linear fit of the depth recorded with the Schlumberger tool string.
From 3683 to 10170 sec: Depth = -0.0714367 * (time - 4400) + 560.288
From 10170 to 10531 sec: Depth = 148.01+(204-148.01)*(time - 10170)/(10531 - 10170)
From 10531 to 12230 sec: Depth = -0.071437 * (time - 10531) + 204
After 12230 sec: Depth = 82.7*(12550 - time)/(12550 - 12230)
FMS/GPIT/NGT Run. The pressure data has been initially smoothed using a 300-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 = 565 * (Pressure - 98)/(159.7 - 98)
where
Depth = mbsf
Pressure = bars
159.7 bars = maximum pressure recorded
98 bars = pressure at mudline
565 mbsf = maximum logged depth
The procedure described for the DIT and FMS runs 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.
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