  This paper reviews theories, experimental data, and modeling methods for
pre-Darcy flow in low-permeability porous media, where Darcy velocity shows
nonlinear dependence on pressure gradients at sufficiently low pressures, a
deviation from Darcy's law. It begins by explaining the fundamental mechanisms
of pre-Darcy flow, focusing on its unique characteristics like non-linear
pressure gradients and fluid-rock interactions. Next, the paper compiles
experimental studies on low-permeability geomaterials such as tight sandstones,
shales, and clays, detailing methodologies employed, including core sample
preparation, permeability measurement techniques, and threshold pressure
gradient assessments. The experiments' findings, showing how pore geometry,
fluid type, and pressure conditions affect pre-Darcy flow onset, are discussed.
The review then covers empirical and theoretical models, plus simulation
methods developed for interpreting data on pre-Darcy flow. It concludes by
highlighting challenges in conducting and interpreting these experiments,
suggesting directions for future research. This comprehensive analysis aims to
assist those studying fluid dynamics in low-permeability geomaterials and has
implications for applications like shale oil and gas recovery, contaminant
transport in low-permeability aquifers, and geological nuclear waste disposal.
