Core Total Gamma-Ray Logger
Model 510
Total
Gamma-Ray Logger
The
natural gamma-ray radiation emitted from rocks varies with the lithology. The radiation comes from the radioactive
decay of Uranium, Thorium, and Potassium, present as trace elements. Shale is composed of more of these elements
than a clean sandstone or limestone.
Generally, the greater the shale content, the greater is the quantity of
radiation.
A
gamma-ray well log is a recording of the natural gamma radiation of the
formation around the well bore and is almost always run in conjunction with
other well logs. Because the gamma-ray
log does not change with well treatment or production, it can be used to
correlate the depths of the other well logs and the core gamma-ray log
from the same hole.
The
Model 510 Total Gamma-Ray Logger measures and records the sum
total of the natural radiation emitted from the test core, whereas the Model 560 Spectral Gamma-Ray Logger
measures the radiation and determines the relative quantities of potassium,
uranium, and thorium, and additionally, the total of the radiation.
The
core gamma-ray log is recorded on the same vertical (depth) scale as the well
log so that the well log and the core gamma-ray log can be overlain. The quantity of gamma radiation from the
core is proportional to that measured in the well, although not the same
because of the difference in the masses of the core and that of the earth
surrounding the well bore.
The
Core Gamma-Ray Logger is built around a six-inch wide by 7.5-foot long
(15cm X 2.3M) conveyor. The belt speed
is variable from about .25 to 6 feet/minute (.08 to 2 meters/min). The slower the travel, the greater is the
definition of the core gamma-ray log of a small diameter core. Belt travel and radiation data are collected
by the PC compatible computer. The belt
is synchronized to the gamma-ray readings with a shaft encoder interfaced to
the computer. The gamma-ray detector is
a 3 inch x 3 inch NaI crystal mounted
under the conveyor belt so that the distance between the core and detector will
not vary with the core size.
Approximately 450 lbs (204 kg) of low activity lead protect the detector
from ambient radiation. The detection
electronics include preamplifier, amplifier, discriminator, and high voltage
bias supply.
The
core gamma-ray log data and data identifying the core are recorded on a
3.5-inch floppy disk. Input of the core
identity and collection of the data is controlled from the menu driven
program. The data are displayed on the
monitor in the well log format continuously as they are taken. The core gamma-ray log may be printed on a
dot matrix printer included in the system.
Available
options are: 50Hz-230 volt operation at no added cost, and 8-inch wide
conveyor, or added length at additional cost.
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