Lab Measurements of Noble Gas Capture from Water Saturated Non Welded Tuff

Abstract:

This work extends research directed towards developing the concept of noble gas release as a deformation signal. Geogenic noble gases are probably contained in all crustal rocks. These gases represent a unique signal source, their release may be related to deformation state of rock; sensing this signal will inform us of natural and anthropogenic deformation. We have developed a laboratory system to measure helium released during deformation of a jacketed, fully saturated tuff in a triaxial cell. The lithology studied is a Tertiary nonwelded tuff with ~50% pretest porosity.

Six undrained water-saturated triaxial constant mean stress (CMS) tests with mean stress ranging from 25 to 200 MPa were completed. Posttest measurements of helium represent gas apparently released during the deformation. Helium was successfully captured from all samples, the released gas flows through a water trap system and then into a helium mass spectrometer. Some helium resided in the pore and line water, and this amount was determined from a replica test on a steel billet.

A burst of helium is observed upon exposing the sample to the gas analysis system, followed by a general decay in helium flow rate with increasing time over 1-2 hours. During this time, one or more additional bursts of helium are observed as the sample is drained of helium. The helium flow rate depends on gas flow/availability and permeability of the deformed sample. For field measurements, our laboratory results imply that continuous measurements may be differently informative than grab samples. The test system and lab measurements will be detailed.

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. SAND2020-6943 A