Neutron diffraction measurement of pore pressure influence on lattice strains in geological materials

The laboratory experiments typically performed to measure poroelastic properties evaluate the macroscopic deformation of samples. While these techniques are adequate for capturing bulk effects, they fail to capture fine detail related to the actual deformation of constituent mineral phases because the measurement captures the combined effect of pore network geometry change and polymineralic deformation. A more precise measurement of mineral deformation in fluid saturated porous media has the potential to improve understanding of poroelastic behavior and material failure where pore pressure is present. Neutron diffraction has emerged as a unique and powerful technique for measuring the localized lattice strains of mineral phases inside of geological materials. The highly penetrating nature of neutrons also permits interrogation of the interior regions of geological samples even when they are contained in otherwise difficult to access or opaque structures such as pressure vessels. This paper summarizes a set of neutron diffraction experiments that were performed with geological materials of varying porosity and permeability using a custom-designed triaxial pressure cell. The results confirm that neutron diffraction has the potential to become a useful tool for quantifying the behavior of distinct crystalline phases within porous media.