Wireline Temperature Data Processing


ODP logging contractor: LDEO-BRG
Hole: 803D
Leg: 130
Location: Ontong-Java Plateau (NW Pacific Ocean)
Latitude: 2° 25.98' N
Longitude: 160° 32.46' E
Logging date: February, 1990
Bottom felt: 3424 mbrf
Total penetration: 656 mbsf
Total core recovered: 494.9 m (75.5 %)


Water Depth: 3412.2 mbsl
Temperature Tool Used: LDEO-TLT
Depth versus time recording available: NO



Logging Runs


Logging string 1: DIT/HLDT/SDT/NGT
Logging string 2: FMS/GPIT/NGT
No information available from the logging report or log header about use of the wireline heave compensator to counter ship heave.




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


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 = BD *(Pressure-MudlineP)/(Pmax- MudlineP)




Depth = mbsf

BD = bottom depth (mbsf)

Pressure = bars

Mudline P = bars

Pmax = pressure at bottom depth (bars)


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 794D:


Mudline P=341 bars
Pmax=414 bars at 650 mbsf
Depth  = 650*(Pressure - 341)/(414 - 341)
Depth calculated from pressure at mudline and maximum depth logged

Logging Run: FMS/GPIT/NGT
Mudline P=347.5 bars
Pmax=416 bars at 610 mbsf
Depth  = 610*(Pressure – 347.5)/(416 – 347.5)
Depth calculated from pressure at mudline and maximum depth logged

Information about the temperature logging operations can be found in the Site Chapter (Operations, Downhole Measurements, and Heat Flow sections), ODP IR volume 130.



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