Wireline Temperature Data Processing
ODP logging
contractor: LDEO-BRG
Well name: 792E
Leg: 126
Location: Izu Bonin Forearc (NW Pacific)
Latitude: 32° 23.96' N
Longitude: 140° 22.79' E
Logging date: May, 1989
Bottom felt: 1798.2 mbrf (used for depth shift to sea floor)
Total penetration: 885.9 mbsf
Total core recovered: 361.9 m (48.2 %)
Water Depth: 1787.7 mbsl
Temperature
Tool Used: LDEO-TLT
Depth versus time recording available: NO
Logging
Runs
Logging string 1: DIT/LSS/NGT
Logging string 2: FMS/GPIT/NGT (Pass 2)
Logging string 3: ACT/GST/NGT
Logging string 4: HLDT/LSS/NGT
The wireline heave compensator was used to counter ship heave during the first two runs but failed at the beginning of the third and was discontinued.
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).
A linear relationship of pressure versus depth has been calculated from the pressure reading at the mudline and at the total logging depth for each logging run. 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. The pressure readings are then converted to depth using a pressure/depth conversion that is linearly interpolated between the values determined at the mudline and total logging depth.
Depth = Pressure * x - WD
where
Depth = mbsf
Pressure = bars
x = pressure conversion coefficient (m/bars)
WD = mbsl
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.
The following processing has been performed at Hole 792E:
Mudline (?) P=178 bars at 137-357 sec
x=WD/178=10.043
Pmax=269 bars at 5876 sec
x=(WD+877.1)/269=9.906
Pressure conversion factor
calculated from average of pressure at mudline and bottom of interval logged,
DIT and GLT runs
Depth=Pressure * 9.990-1787.7
Logging Run: FMS/GPIT/NGT (Pass 2)
Mudline (?) P=181 bars at 170-600
sec
x=WD/181=9.877
Pmax = 271 bars at 2272 sec (down
and up-going, both good)
x=(WD+878.6)/271=9.839
Pressure conversion factor
calculated from average of pressure at mudline and bottom of interval logged,
FMS and HLDT runs
Depth=Pressure * 9.867 - 1787.7
Mudline (?) P=177 bars at 15-389
sec
x=WD/177 =10.100
Pmax = 269 bars at 2597 sec
(begins up-going)
x=(Wd+878)/269=9.910
Pressure conversion factor
calculated from average of pressure at mudline and bottom of interval logged,
DIT and GLT runs
Depth=Pressure * 9.990-1787.7
Logging Run: HLDT/LSS/NGT
Mudline (?) P= 181 bars at 154-397
sec
x=WD/181=9.877
Mudline (?) P= 208 bars at
649-1071 sec
Pmax = 270 bars
(WD+878)/270=9.873
Pressure conversion factor
calculated from average of pressure at mudline and bottom of interval logged,
FMS and HLDT runs
Depth=Pressure * 9.86 -1787.7
Information about the temperature logging operations can be found in the Site Chapter (Operations, Downhole Measurements, and Heat Flow sections), ODP IR volume 126.
Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia