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.