Hydromechanical characterization of gas transport amidst uncertainty for underground nuclear explosion detection

Journal Article · Fri Dec 01 00:00:00 EST 2023 · Journal of Rock Mechanics and Geotechnical Engineering

DOI:https://doi.org/10.1016/j.jrmge.2023.09.018· OSTI ID:2246978

Li, Wenfeng; Neil, Chelsea W. ; Carey, J. William ; Meng, Meng; Frash, Luke P. ; Stauffer, Philip H.

Given the challenge of definitively discriminating between chemical and nuclear explosions using seismic methods alone, surface detection of signature noble gas radioisotopes is considered a positive identification of underground nuclear explosions (UNEs). However, the migration of signature radionuclide gases between the nuclear cavity and surface is not well understood because complex processes are involved, including the generation of complex fracture networks, reactivation of natural fractures and faults, and thermo-hydro-mechanical-chemical (THMC) coupling of radionuclide gas transport in the subsurface. In this study, we provide an experimental investigation of hydro-mechanical (HM) coupling among gas flow, stress states, rock deformation, and rock damage using a unique multi-physics triaxial direct shear rock testing system. The testing system also features redundant gas pressure and flow rate measurements, well suited for parameter uncertainty quantification. Using porous tuff and tight granite samples that are relevant to historic UNE tests, we measured the Biot effective stress coefficient, rock matrix gas permeability, and fracture gas permeability at a range of pore pressure and stress conditions. The Biot effective stress coefficient varies from 0.69 to 1 for the tuff, whose porosity averages 35.3% ± 0.7%, while this coefficient varies from 0.51 to 0.78 for the tight granite (porosity <1%, perhaps an underestimate). Matrix gas permeability is strongly correlated to effective stress for the granite, but not for the porous tuff. Our experiments reveal the following key engineering implications on transport of radionuclide gases post a UNE event: (1) The porous tuff shows apparent fracture dilation or compression upon stress changes, which does not necessarily change the gas permeability; (2) The granite fracture permeability shows strong stress sensitivity and is positively related to shear displacement; and (3) Hydromechanical coupling among stress states, rock damage, and gas flow appears to be stronger in tight granite than in porous tuff.

• Research Organization: Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
• Sponsoring Organization: USDOE Laboratory Directed Research and Development (LDRD) Program; USDOE National Nuclear Security Administration (NNSA)
• Grant/Contract Number: 20220019DR; 89233218CNA000001
• OSTI ID: 2246978
• Alternate ID(s): OSTI ID: 2281508
• Report Number(s): LA-UR-23-24703; S1674775523003232; PII: S1674775523003232
• Journal Information: Journal of Rock Mechanics and Geotechnical Engineering, Journal Name: Journal of Rock Mechanics and Geotechnical Engineering; ISSN 1674-7755
• Publisher: Elsevier
• Country of Publication: China
• Language: English

Related Subjects

underground nuclear explosion uncertainty quantification
radionuclide transport
biot effective stress coefficient
fracture permeability
matrix permeability