Elimination of Heat-Shielding for Geothermal Tools Operating Up To 300 Degress Celsius Page: 1 of 7
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Elimination of Heat-Shielding for Geothermal Tools Operating Up To 300 Degrees Celsius
Randy Normann and Joseph Henfling
Sandia National Laboratories, MS 1033, PO
KEYWORDS: Silicon-On-Insulator, High-Temperature
Electronics, Thermal Batteries
This report focuses Sandia National Laboratories' effort to
create high-temperature logging tools for geothermal
applications NOT requiring heat-shielding. Tool electronics
can operate up to 300*C with a few limiting components
operating to 250*C. Second generation electronics are
needed to increase measurement accuracy and extend the
operating range to 300* and then 350*C are identified.
Custom development of high-temperature batteries and
assembling techniques are touched on. Outcomes of this
work are discussed and new directions for developing high-
temperature industry are suggested.
In the past 30 years, electronics have been qualified for
operating within three temperature ranges: commercial,
industrial and military. New higher temperature
applications for commercial and military aircraft have
pushed for the development of new high-temperature
electronics, creating a new 225*C standard, . Table 1
provides the fore mentioned temperature ranges in degrees
Celsius and Fahrenheit.
These new high-temperature components are based
primarily on Silicon-On-Insulator (SOI) technology. Figure
1, shows a CMOS transistor pair constructed using common
bulk silicon and SOI. The buried oxide layer, in SOI, forms
a non-conducting layer where the N-substrate common to
lower temperature electronics is a semi-conductor material.
This buried oxide layer reduces leakage current by a factor
approaching 100X, .
Obviously, the benefit of this new technology is the
possibility of displacing (or reducing) the Dewar (heat-
shield). At present, the Dewar flask is one of the highest
cost components in any geothermal logging tool, . If
high-temperature electronics can displace the Dewar flask
there are significant benefits. Following is a list of benefits
of Dewarless and Dewared tools.
Advantages of HT electronics over Dewared tools.
" Unlimited time downhole where the Dewar flask
provides only 8-12 hrs in most applications.
" Reduced tool outer dimension, where the flask adds a
50-100 mm to the outer diameter.
" Reduced tool cost by both reducing possible tool
damage downhole from overheating and replacing the
expensive Dewar flask.
Advantages of Dewaring tools
" Broader range of electronic components to choose from
when designing a logging tool.
Box 5800 Albuquerque, NM 87185
" Normally, higher accuracy measurementus f
greater component selection and redu g
Work at Sandia National Laboratories is to demons
designs for operating up to 300 C and to encourage the
continued development of electronic devices to regain
measurement accuracy at those elevated temperatures. The
goal of this report is to relate Sandia on-going activities and
discuss high-temperature issues.
For the purposes of this discussion, a very simple block
diagram showing the needed elements in most downhole
instruments is shown in Figure 2.
Working from the bottom of Figure 2 and up. First the
sensors measure wellbore information and convert it to a
voltage or electrical frequency. These changes in voltage or
frequency are then conditioned by analog circuits in a form
acceptable for conversion from analog to digital. Once in
digital form, the microprocessor can either store the result in
memory or transmit it to the surface.
All electronic circuits need power, normally DC voltage and
current. Power can either be sent down via an e-line or self-
contained within the tool by use of high-temperature
High-temperature sensors can be broken down into three
categories; readily available, soon to be available, may never
2.1Readily Available: Many geothermal sensors are already
available for high-temperature applications. This is true
because these sensors were already making direct contact
with the wellbore environment in conventional logging
tools. Sensors as temperature, acoustic, strain, and spinner
can be found as off the shelf items.
2.2 Soon to be Available: Some sensors, like pressure
sensors, were housed inside the Dewar flask with only a
small pressure port leading to the wellbore. For a Dewarless
pressure tool, new pressure sensors will be required. At
present, we at Sandia are aware of several companies
working on high-accuracy, high-temperature pressure
Other sensors didn't require wellbore exposure. For
example, the measure of magnetic fields and/or vibration
could be done inside the Dewared housing. There exists
reasonable evidence that magnetometers and accelerometers
can be produced for 300 C. Here, the use of high-
temperature materials can lead to new high-temperature
sensors based on older technology.
2.3 May Never be Available: Still, other sensors like
Sodium Iodide [NaI(TI)] used for gamma spectroscopy will
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HENFLING,JOSEPH A. & NORMANN,RANDY A. Elimination of Heat-Shielding for Geothermal Tools Operating Up To 300 Degress Celsius, article, October 7, 1999; Albuquerque, New Mexico. (digital.library.unt.edu/ark:/67531/metadc628318/m1/1/: accessed May 25, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.