Wireline Temperature Data Processing


ODP logging contractor: LDEO-BRG

Well name: 765D

Leg: 123

Location: Argo Abyssal Plain (SE Indian Ocean)

Latitude: 15° 58.54' N

Longitude: 117° 34.49' E

Logging date: October, 1988

Bottom felt: 5724.3 mbrf

Total penetration: 1194.9 mbsf

Total core recovered: 78.7 m ( %)


Water Depth: 5717.7 mbsl

Temperature Tool Used: LDEO-TLT

Depth versus time recording available: NO


Logging Runs


Logging string 1: DIT/SDT/NGT

Logging string 3: LDT/CNTG/GPIT/NGT

Logging string 2: BHTV

No information could be found about use of wireline heave compensator.


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 = Pressure * x - WD




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 765D:


Logging Run: DIT/SDT/NGT

Mudline (?) P=581 bars at 17695 sec

Pmax=705 bars at 4580 sec



Mudline (?) P=582 bars at 13052 sec

Pmax = 704 bars at 3247 sec


Logging Run: BHTV

No mudline P

Pmax = 703 bars at 5682 sec (begins up-going)


Mudline P averaged from DIT and LDT runs: 581.5 bars


Pmax from LDT run


Pressure conversion factor calculated from average of pressure at mudline (DIT and LDT runs) and bottom of hole (LDT run)

Depth=Pressure * 9.795 - 5713.8


Information about the temperature logging operations can be found in the Site Chapter (Operations, Downhole Measurements, and Heat Flow sections), ODP IR volume 123.


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