Helium (4He) Measurements During a Chemical Explosion and their Implications

Abstract:

Helium (⁴He) is native to rhyolite, accumulates over time at intragranular sites, and was not injected during a recent chemical explosion experiment at a site called Blue Canyon Dome (BCD). From triaxial testing of BCD rhyolite in the laboratory, ⁴He is released in quantities that are readily measurable. Laboratory measurements have shown direct relationships between fracturing and noble gas releases. In the BCD field measurement, we are looking for confirmation that helium and other noble gases are also measurable during field scale fracturing events. Using real-time mass spectroscopy (MS), an extremely sensitive sensor was deployed at BCD for these measurements. This may be the first time that long-term continuous real-time measurements (versus grab sampling) using MS have been made during an anthropogenic or natural rock-fracturing event.

The results were contrary to what we expected. The helium flow rate decreased dramatically at the time of the shot, and the helium flow rate increased back to its background level over the course of 3 weeks after the shot. We interpret the observation as resulting from a flood of water into the sensor vicinity, effectively choking down helium flow. Key take-aways from the measurements are: 1) the signal of the shot was unanticipated yet very apparent; 2) the presence of water effects gas flow measurements; 3) there is a need for long-duration-continuous measurements (versus long-term grab samples), the time for these measurements was probably too short.

Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. SAND2020-7710 A