Coupling Preferential Flow and Flow-induced Strain in Heterogeneous Rock-like Medium 

Abstract

Pressurized fluid injection into underground rocks occurs in applications like carbon sequestration, hydraulic fracturing, and wastewater disposal and may lead to human-induced earthquakes and to surface uplift. Yet, the full mechanical response of the underground to those injections is largely unknown. As the underground cannot be observed directly, experimental studies are crucial for understanding its mechanical reaction to fluid injection. Yet the need to maintain high pressure flow while tracking deformation complexes the execution of such experiments in comparison to standard mechanical tests. In this study we use a unique-transparent porous medium, made from chemically sintered Polymethyl Methacrylate (PMMA) beads, to simulate the underground rocks. We inject into the medium fluid at increasing pressure while measuring its internal plane-strain field as it deforms. We find that although the medium is constrained in its periphery, internal strains still occur perpendicular to the flow, compensated by the medium itself. While the medium’s overall strain shows clear reversibility, the internal perpendicular strain variations show very little to no recovery at all. Flow simulations over permeability fields, derived from the measured strain, reveal that internal strain variations have a significant impact on preferential flow within the medium. Together with the measured strain, the simulations results constitute a strong base for modeling the local heterogenous coupling between preferential flow and deformation in the underground due to fluid injections.