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In the past,
the process of monitoring
down hole well conditions
was unreliable and expensive.
The earliest types of down
hole sensors employed what
is referred to as “PHD
sensor technology". COSCO does
not produce or sell the older
technology, as more advanced
alternatives are now available.
Electronics can now perform
much better in extreme environments.
Today’s technology is
not only more accurate, but
more efficient and reliable
as well. The following discussion
compares the ELECTRONIC sensor
technology to the PHD sensor
technology:
PHD type sensors
have the following characteristics:
- A bourdon
tube is used to measure
pressure. This is a mechanical
device prone to failure
and particularly prone to
damage from impact that
is commonly experienced
while running in the hole.
- By varying
the resistance of the motor
star point to ground, down
hole parameter values can
be determined by calculations
based on resistance measurements
at the surface. A relay
is used to switch between
pressure and temperature
measurements. Being a mechanical
device, a relay is rated
for a limited number of
switching operations. The
most common failure occurs
when the relay eventually
seizes in one position and
only one of the parameters
can be measured.
- Latch and
de-latch features are required
so the insulation resistance
of the system can be measured
accurately with a meg-ohmmeter.
Electronic
sensors are significantly
different as follows:
- Mechanical
devices have been replaced
with more robust solid-state
electronics that do not
rely on moving parts. This
increases reliability and
accuracy and decreases the
chances of damage during
installation.
- Data is
transmitted to the surface
via the main ESP power cable
by means of a digital signal
that is superimposed on
the motor supply voltage.
A surface choke filters
the waveform to isolate
the signal from the high
voltage and a surface RTU
measures, interprets and
stores the data.
- The use
of a digital signal allows
more than two readings to
be transmitted simultaneously.
- Data logging
devices are used at surface
to record readings in electronic
memory. Down hole readings
in addition to power supply
and motor load readings
can all be logged and stored
together. This allows for
a better understanding of
the reservoir and ESP system
conditions as a whole.
- Resistance
to ground values are not
manipulated, hence the latch
and de-latch functions are
not required.
- The RTU
firmware (software program
resident in both the down
hole sensor and the surface
interface panel) can be
updated as new versions
become available.
- Repairs
to the down hole tool can
be easily accomplished by
changing pre-calibrated
circuit boards in the field.
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