Temperature (HTGC) Data Processing
ODP logging
contractor: LDEO-BRG
Hole: 1188F
Leg: 193
Location: Manus Basin
Latitude: 3°43.686'S
Longitude: 151°40.188'E
Logging date: 21 December 2000
Bottom felt: 1653 mbrf
Total penetration: 386.7 mbsf
Total core recovered: 30.9m (18.3%)
Temperature Tool Used: HTGC
Water
Depth: 1652 mbrf
Logging Runs
Logging string 1: DIT/HTGC (main and repeat passes)
Logging string 2: HLDS/APS/HNGS/HTGC (main and repeat passes)
Logging string 3: FMS/GPIT/NGT/DSI/HTGC (2 passes)
The wireline heave compensator (WHC) was
not used on the first logging run because the system would not power up. A
problem was found with the limit switch as the piston extended to a maximum
position sending a current imbalance (current flowing on the ground line) to
the ground fault interrupt (GFI) and causing the GFI to shut the system down.
An external power supply was used to manually move the piston to a middle
position where the limit switch would not affect the system. The WHC was then
used during the second and third tool string deployments.
All logging strings: Bottom-hole assembly at 183 mbsf; casing at 190.5 mbsf
The HTGC (High-pressure, High-temperature Telemetry Gamma-Ray Cartridge) consists of a gamma-ray detector made of a NaI crystal, a photo multiplier tube, a high-voltage generation circuit, and a preamplifier of the gamma-ray pulse all built in one package. The number of the output pulses from the detector is counted at a rate of 8 Hz, and the count is sent up-hole. Housed in a heatsink and dewar flask that allow operations in high-temperature environments (260ÁC), this tool also has a 31-pin upper and lower head asset and is combinable with any standard 3.375-in tool without additional adaptors. The data acquisition software cannot distinguish between the tools, but the HTGC has the correct length and measure point and gamma-ray response for the flasked tool.
The gamma-ray values are measured in
American Petroleum Institute (API) units. These units are derived from the
primary Schlumberger calibration test facility in Houston, Texas, where a
calibration standard is used to normalize each tool. Because the natural
gamma-ray response is sensitive to borehole diameter and the weight and concentration
of bentonite or potassium chloride present in the drilling mud, corrections are
routinely made for these effects during data processing at LDEO-BRG. The HTGC
also has an external sensor that allows for real time temperature measurements
of the borehole fluids. This sensor was located on the cable head that was used
on top of each tool string. Two thermocouples were used to calibrate the cable
head temperature measurements. At 0ÁC there is a -1.1ÁC difference between the
calibration standard and the cable head measurements. At 106ÁC there is a 1.7ÁC
difference.
No processing of the HTGC temperature data was performed. The temperature measurements made on the cable head are ñroughî indicators of borehole conditions because there are post-drilling disturbances and some fluid displacement effects from the entire tool string that can affect the temperature measurements especially in the down logs. The temperature data have been depth shifted to match the other logs by using the gamma ray measurement recorded with temperature.
For additional information contact:
Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia