Influence of pore fluid viscosity and fluid-clay interactions on the hydromechanical response of resedimented kaolinite

Abstract

Understanding how pore fluid properties influence the hydromechanical behavior of clay-rich formations is essential for evaluating the performance and long-term stability of subsurface geoenergy systems, including caprock integrity, storage containment, and unconventional reservoir response. This study investigates the coupled influence of pore fluid viscosity and interfacial interactions (polarity and dielectric constant) on the consolidation and creep behavior using resedimented kaolinite mudrocks. One-dimensional consolidation tests were performed using polar, high-dielectric, low-viscosity NaCl brine and nonpolar, low-dielectric, high-viscosity hydraulic oil as pore fluids to isolate fluid effects on compressibility, permeability, and time-dependent deformation. While both fluids exhibited similar compression indices, differences emerged in drainage kinetics and creep behavior. A modified semi-empirical consolidation model was introduced to consider viscosity and interfacial interactions through a porosity-permeability power law and a viscosity-scaled creep function. This combined experimental–modeling approach provides a new basis for separating hydrodynamic and interfacial controls on the time-dependent behavior of kaolinite-rich mudrocks. Sensitivity analyses were used to determine the fluid-dependent exponents in the porosity–permeability relationship, and the resulting differences were interpreted in terms of the combined effects of fluid viscosity and interfacial interactions. These results highlight that pore fluid hydrodynamic and interfacial properties jointly govern consolidation kinetics and long-term deformation in kaolinite mudrocks, providing insights relevant to clay-rich geoenergy systems.