Temperature Data Processing

 

ODP logging contractor: LDEO-BRG

Hole: 1201D

Leg: 195

Location: Philippine Abyssal Plain (Philippine Sea)

Latitude: 19° 17.8165' N

Longitude: 135° 5.9519' E

Logging date: April 12, 2001

Bottom felt: 5720 mbrf

Total penetration:  800 mbsf

Total core recovered:  406.8 m (67.8 %)

Water Depth: 5725 mbrf

Temperature Tool Used: LDEO-TAP

Depth versus time recording available: No depth data was recorded due to frequent crashes of the acquisition PC.

Logging Runs

Logging string 1: DLL/APS/HLDT/HNGS

The wireline heave compensator was used to counter minor ship heave.

Tool Information

The TAP tool acquires borehole temperature, tool acceleration, and hydrostatic pressure. It may be run in either memory mode, where the tool is fastened to the bottom of logging string and data is stored in the on-board memory, or in telemetry mode, where the tool is run alone and data is recorded in real-time by the third-party data acquisition system. When the tool is run in memory mode, the stored data is dumped to the third party data acquisition system upon the tool's return to the rig floor.

Borehole fluid temperature is recorded with one thermistor located at the bottom of the tool. The internal temperature of the tool is recorded as well. A pressure transducer is included to turn the tool on and off at specified depths when used in memory mode. Typically, data acquisition is programmed to begin 100 m above the seafloor. A 3-axis accelerometer is also included to measure tool movement down hole. These data are expected to be instrumental in analyzing the effects of heave on a deployed tool string which will lead to the fine tuning of the WHC (wireline heave compensator).

Limitations

Drilling and circulation operations considerably disturb the temperature distribution inside the borehole, thus preventing equilibrated temperature conditions. The amount of time elapsed between the end of drilling fluid circulation and the beginning of logging operations is not long enough to allow the borehole to recover thermally.

Data Processing

During this leg no depth versus time data was recorded, due to frequent crashes of the acquisition PC. Therefore, 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 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)

where

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.

The following processing has been performed at Hole 1201D:

Logging Run: DIT/APS/HLDT/NGT

Mudline P=580.5 bars

Pmax= 658.3 bars at 840 mbsf

Depth = 575*(Pressure - 580.5)/(658.3 - 580.5)

Information about the temperature logging operations can be found in the Operations, and Downhole Measurements chapters, ODP IR volume 195.

For any question about the data or about the LogDB database, please contact LogDB support: logdb@ldeo.columbia.edu.