Search

Two longstanding goals in subsurface science are to induce fractures with a desired geometry and to adaptively control the interstitial geometry of existing fractures in response to changing subsurface conditions. Here, we demonstrate that microscopic mineral fabric and structure interact with macroscopic strain fields to generate emergent meso-scale geometries of induced fractures. These geometries define preferential directions of flow. Using additively manufactured rock, we demonstrate that highly conductive flow paths can be formed in tensile fractures by creating corrugated surfaces. Generation, suppression and enhancement of corrugations depend on the relative orientation between mineral fabric and layering. These insights into the role of micro-scale structure on macro-scale flow provide a new method for designing subsurface strategies to maximize potential production or to inhibit flow. [ABSTRACT FROM AUTHOR]

This work explores the effects of oriented layers and texture (oriented minerals) on fracture evolution in 3D printed gypsum samples. During 3D printing, bassanite (calcium sulfate hemihydrate) was chemically transformed into gypsum layer by layer, giving rise to anisotropic texture. Unconfined compressive strength (UCS) tests monitored with six broadband acoustic emission (AE) transducers were performed with cylindrical specimens: casted gypsum (CG) samples, and 3D printed (3DP) samples with five different orientations of bassanite layer and gypsum texture relative to the loading direction. UCS varied by 150% among the samples, primarily due to anisotropy in the 3DP samples. The bonds of gypsum crystals between sequential bassanite layers were stronger than those of gypsum-bassanite, resulting in anisotropic material properties. Unlike the CG samples, no axial splitting was observed from the 3DP samples, and a single inclined (relative to loading direction) major crack was observed instead. The fracture location estimated by AE localization technique was comparable to that observed from reconstructed X-ray computed tomography images. CG samples failed immediately after reaching a peak load, while 3DP samples exhibited ductile post-peak behavior. Examination of the AE signal amplitude from post-peak loading revealed that more ductile behavior was associated with more AE events that occurred over a longer period of time, and the resultant fracture surfaces were rougher than for narrow distributions. Monitoring of AE signals during failure of rock has the potential to predict fracture roughness and the mineral and layering patterns. [ABSTRACT FROM AUTHOR]