Wireline Standard Data Processing
ODP logging
contractor: LDEO-BRG
Hole: 793B
Leg: 126
Location: Izu-Bonin Forearc (NW Pacific)
Latitude: 31° 6.33' N
Longitude: 140° 53.27' E
Logging date: June, 1989
Bottom felt: 2975.3 mbrf
Total penetration: 1682 mbsf
Total core recovered: 697.9 m (63.7 %)
Water Depth: 2964.8 mbsl
Temperature
Tool Used: LDEO-TLT
Depth versus time recording available: NO
Logging
Runs
Logging string 1: DIT/LSS/NGT (3 passes)
Logging string 2: FMS/GPIT/NGT (upper and lower sections)
Logging string 3: ACT/GST/NGT (upper and lower sections)
No information available about use of wireline heave compensator to counter ship heave.
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 793B:
Mudline (?) P=304 bars
x=WD/304=9.753
Pmax=374 bars
x=(WD+708.2)/374 = 9.821
Pressure conversion factor
calculated from pressure at bottom of interval logged, pass 1
Depth=Pressure * 9.821 - 2964.8
Logging Run: DIT/LSS/NGT (pass 2)
Mudline P=297 bars at 140 sec
x=WD/297=9.982
Pmax=396bars at 2840 secs
x=(WD+947.8)/396=9.880
Pressure conversion factor
calculated from average of pressure at mudline and bottom of interval logged
Depth=Pressure * 9.931 - 2964.8
Mudline P=303 bars
x=WD/303=9.785
Pmax=473 bars
x=(WD+1565.6)/473=9.578
Pressure conversion factor
calculated from average of pressure at mudline and bottom of interval logged
Depth=Pressure * 9.682 - 2964.8
Logging Run: FMS/GPIT/NGT (pass 1)
Mudline P=297 bars
x=WD/297=9.982
Pmax=466 bars
x=(WD+1539)/466=9.665
Pressure conversion factor
calculated from average of pressure at mudline and bottom of hole
Depth=Pressure * 9.824 - 2964.8
Mudline P=302 bars
x=WD/302=9.817
Pmax=467 bars
x=(WD+1531/467=9.627
Pressure conversion factor calculated
from average of pressure at mudline and bottom of interval logged
Depth=Pressure * 9.722 - 2964.8
Logging Run: FMS/GPIT/NGT (pass 2)
Mudline P=297 bars
x=Wd/297=9.982
Pmax=374 bars
x=(WD+764)/374=9.970
Pressure conversion factor
calculated from average of pressure at mudline and bottom of interval logged
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