HIGH TEMPERATURE-PRESSURE SFAI TOOL

The purpose of this work was to develop a high temperature-/high pressure-capable instrument that could be used to characterize the brines of Enhanced Geothermal Systems in terms of their temperature, pressure, salt concentration, and flow rate of fluids.  We used a technique called Swept Frequency Acoustic Interferometry (SFAI) which uses the frequencies of many acoustic resonances to determine the speed of sound in a medium.  From the speed of sound, as well as complementary measurements, the parameters mentioned above could be determined.  To use SFAI, we had to develop a ruggedized instrument out of high temperature tolerant materials. Our solution consisted of lithium niobate transducers encased in Swagelok and Conflat fittings (to protect the transducers from the harsh environment).  In our lab, we successfully tested our instrument at temperatures up to 300 °C and pressures up to 3000 psig and used it to measure the acoustic properties of pure water, several brines, and Fluorinert.

More details about the instrument, as well as representative data, can be found in this paper.

Click on any image to enlarge:

The high temperature/high pressure test environment in our lab. The pressure vessel (top right) sits inside a furnace rated to      500 °C and a pressure amplifier (on the bottom of the cart) allowed us to reach pressures above 3000 psig.	A close up of our pressure vessel with various gas inlets, pressure gauges, and thermocouples for characterizing the environment.
The high temperature lithium niboate transducer is hermetically sealed from the harsh environment using a combination of Swagelok compression fittings and Conflat components with copper gaskets.	The entire high temp/high pressure SFAI tool, consisting of two transducers arranged in an opposing geometry.  The resonant cavity (8.848 mm in length) is filled with liquid when the tool is immersed in the pressure vessel above.