TEMPERATURE DATA PROCESSING
Hole: 831B
Leg: 134
Water Depth: 1066.4 mbsl
Temperature
Tool Used: LDEO-TLT
Depth versus time recording available: NO
Logging
Runs
Logging string 1: DIT/SDT/HLDT/NGT
Logging string 2: FMS/GPIT/NGT
Logging string 3: ACT/GST/NGT
Logging string 4: NMRT/SUMT
No information available from logging reports 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 831B:
Logging Run: DIT/SDT/HLDT/NGT
Mudline P=104 bars at 682 sec and
104 at 10,933 sec
x=WD/104=10.253
Pmax=191-192 bars at 3896 sec
x=(WD+820)/192= 9.825
Pressure conversion factor
calculated from pressure at bottom of logged interval, DIT and FMS runs.
Quality of downlog better than
uplog.
Logging Run: FMS/GPIT/NGT
Mudline P=106 bars at 511 sec
x=WD/106=10.060
Pmax = 192 bars at 2,288 sec
x=(WD+820)/192=9.825
Pressure conversion factor calculated from pressure at bottom of logged interval, DIT and FMS runs.
Logging Run: ACT/GST/NGT
Mudline P=103 bars at 560 sec
x=WD/103=10.3535
Pmax = 183 bars at 1,948 sec
x=(WD+745)/183=9.898
Pressure conversion factor
calculated from pressure at bottom of logged interval, DIT and FMS runs.
Quality of downlog better than
uplog.
Logging Run: NMRT/SUMT
Mudline P=107 bars at 750 sec
x=WD/107=9.966
Pmax = 186 bars at 2,215 sec
x=(WD+745)/186=9.739
Pressure conversion factor calculated from pressure at bottom of logged interval, DIT and FMS runs.
Despite the four runs, there is not a big change in temperature from run to run. The pressure conversion factor was calculated from pressure at the bottom of the hole in runs 1 and 2.
Depth=Pressure * 9.825 - 1066.4
Information about the temperature logging operations can be found in the Site Chapter (Operations, Downhole Measurements, and Heat Flow sections), ODP IR volume 134.
Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia
Trevor
Williams
Phone: 845-365-8626
Fax: 845-365-3182
E-mail: Trevor Williams