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All Rights Reserved
NEW for 2011… WELLOG is
producing Scintillation Gamma logging tools!
Ask WELLOG about
pricing and availability.
APPLICATIONS:
A Scintillation gamma log is the best
method to provide a quick, low cost correlation of producing zones in a water well or oil well.
The same tool has applications in:
Mining; Uranium mining is gaining emphasis with increasing uranium
prices.
Coal
Bed methane drilling and exploration. Correlation logging on CBM wells is an important aspect of drilling.
Well logging in the environmental industry creates a need for scintillation gamma
ray logging.
Tracer logging in oil production wells which also
includes monitoring secondary fluids in secondary recovery projects.
Scintillation gamma is the most useful
log for providing formation depths, type, and thickness. It is used for
identification of sand, clay, shale formations in all types of wells.
WHERE IT WORKS:
Scintillation gamma works in both cased
and open holes. This method can be used to define lithology on wells that have NO
DRILLING LOG or other records.
THE SYSTEM:
A scintillation gamma tool is connected
to a wireline cable. The wireline cable is connected to a winch that is
used to lower the tool into the well. The tool is lowered to the bottom
of the well and then slowly raised to the surface. As the tool is raised,
it measures the natural gamma radiation in the different formations. Depth of
the measurement is also recorded. The result is recorded as a log of formation
type based on gamma ray count rate related to depth and stored on a computer.
A computer generated final print (well log) is given to the customer.
HOW IT WORKS:
The scintillation gamma tool measures
the natural gamma radiation emitted by the formations thru which it passes.
Clay and shale formations emit more radiation than clean sandstone or limestone
formations. A specialized crystal material referred to as a Sodium Iodide
scintillation crystal is used. The scintillation crystal emits photons of
light when gamma rays enter. The intensity of the light is proportional to the
energy of the gamma ray. Gamma rays have different energies depending on their
source. Pulses of light from the scintillation crystal are detected by a
photo-multiplier tube and are amplified many thousands of times. The result is
an electrical voltage pulse. Depending on the amount of gamma radiation, many
pulses are produced by the photo-multiplier tube. The photomultiplier tube has a certain amount
of low-level noise. A circuit called a discriminator is used to establish a
threshold above the noise voltage in order to not detect noise pulses and allow
only those pulses that exceed the discrimination level to pass. After pulses go
through pulse amplification and waveform shaping, they are counted by a count
rate meter. The output of a count rate meter is a DC voltage that is
proportional to the number of counts. The resulting output voltage is recorded
as a gamma ray counts. Scintillation detectors are considered the most
sensitive type of gamma ray detector.
WHAT IS MEASURED?
All materials are radioactive. Some are
more radioactive than others. Shales and clays are more radioactive than other
natural occurring materials within the earth with the exception of known
radioactive materials containing uranium, thorium, or potassium. Each of these
radioactive materials are found in other materials in
varying amounts. Gamma rays have a specific energy that is measured in
thousands of electron volts (Kev) or millions of electron volts (Mev).
WHY IS IT USEFUL?
A scintillation gamma log provides
useful information about what types of formations are located in a well. It
helps in the final design of a well to determine the proper location of the
perforated section of casing in the well. Since water is commonly produced from
formations that contain mostly sand (sandstone) or lime in the form of
limestone, it is very important to know where these formations are located and
how thick they are. Formations containing a high amount of clay are generally
considered poor formations to produce water. If a water
well is drilled into bedrock, it is possible that perforations may be
inadvertently placed at or below bedrock. If bedrock is not fractured or
otherwise able to produce water in the case of a water well, then the well will
be non productive.
The scintillation gamma tool has
applications in uranium mining.
Coal exploration wells can be logged to
determine the thickness of coal seams. In coal bed methane wells, (CBM
wells) correlation logging can establish accurate definition of coal seams and
their relation to casing joints after casing is installed.
Wells having radon or radium producing
formations can be logged to find potential problem areas.
Because uranium is an important mineral
– uranium exploration wells are often logged to find the formations that are
most favorable for production of uranium. Mineral exploration is an example of
an application where formation definition is important. Because mineral
deposition is frequently associated with formation contact zones, and veins
having high silica content are distinct from surrounding wall rock formations,
a scintillation gamma log may be used. See our webpage on spectral gamma
logging. WELLOG produces spectral gamma logging tools.
FOR MORE INFORMATION:
For more information contact WELLOG at info@wellog.com