In the GNG Project 2: Understand, we are studying the thermodynamics of geochemical reactions at supercritical conditions. We do this by performing complex fluid-rock interaction experiments. The Experimental Geochemistry Laboratory at GNS Science specialises in these high temperature and pressure experiments. In order to extend our capabilities into higher temperature supercritical conditions, we set up a completely new reactor capable of working at temperatures beyond our previous 400°C limit.
Setting up a continuous flow reactor to study supercritical fluid-rock interaction has been a challenging journey.
The one-of-a-kind reactor was designed and manufactured to accommodate our needs. The 220 ml reactor is made from a resistant alloy, capable in maintaining reactions at 700°C and 290 bar.
After installing the reactor, a series of test was preformed in order to evaluate the reactor’s capabilities. It was tested in a configuration known as “batch type”. In such a configuration the reactor is filled with fluid and rock material, sealed, and heated up, resulting in an increase of pressure in the reactor.
Batch reactors are widely used to study thermodynamic properties of mineral-fluid mixtures. In these experiments, fluid and rock chemically react with each other in a closed system for a predetermined length of time. The reactions eventually reach chemical equilibrium and at the end of the experiment the reacted rock is compared with unreacted material.
The sampling of fluids during a high pressure and temperature batch experiment is difficult without disturbing the experiment. This limits the number of samples that can be taken and our ability to understand many processes that have taken place during the experiment.
The alternative to batch-type reaction is the continuous flow approach. A flow-through configuration allows the solution to flow continuously through the reactor, providing fluid samples that can be regularly collected and analysed during the experiment. This offers much more insight into processes occurring in the experiment over time. Flow-through systems can also provide better control overpressure and temperature and enhance work safety.
Setting up a flow-through reactor requires supplementary equipment, but also the need for a completely different approach as the fluid dynamics have a strong influence on the reactions.
No previous attempt to create an extreme temperature (up to 700°C) supercritical flow-through system is known to us. Therefore, a prototype was needed to test the concept before investing in additional equipment. As a proof of concept, existing equipment was modified to fit the purpose, and we successfully attained continuous fluid flow at supercritical conditions.
Going forward, after testing the successful prototype, supplemental equipment was purchased and installed. This included a new back pressure regulator system, a high-pressure liquid pump, an additional temperature controller, a fume extraction hood, and a new uninterruptable power system to keep everything running smoothly.
Today our supercritical flow-through reactor allows the comprehensive study of interactions between geothermal brines and Aotearoa New Zealand’s reservoir rocks at temperatures and pressures up to 700°C and 290 bar. We look forward to sharing our results from upcoming experiments in the coming year.