A critique on “Modeling the spontaneous imbibition of non-Newtonian fluids into the fractal porous media of tight reservoirs”

Abstract

In February 2022, this journal published the paper “Modeling the spontaneous imbibition of non-Newtonian fluids into the fractal porous media of tight reservoirs” (Zhu et al., 2022), which develops and validates an analytical model for the capillary absorption of (non-)Newtonian liquids in sandstone, founded on a fractal-based bundle-of-tubes model. This critique – a post-publication review – expresses concerns on that model development and validation. It is shown that agreement between calculated and measured absorbed moisture masses and moisture front heights is only attained with two strongly distinct sets of material and fluid properties, a dichotomy that is however not disclosed in the paper. It is moreover revealed that the input material and fluid properties and the output absorbed moisture masses and moisture front heights often defy physical plausibility. Detailed scrutiny of the mathematical model complementarily exposes concrete defects in the calculation of the ‘sample’ cross-section. It is displayed that this cross-section calculation is exclusively governed by the material properties, implying that the measured cross-section can (almost) never be equated. It is furthermore established that the cross-section calculation assumes the equality of the areal and volumetric porosity, which is incorrect for a bundle-of-tubes with tortuous capillaries. Additionally it is demonstrated that the cross-section calculation merges two conflicting relations between the porosity and the fractal properties. All these concerns bring about doubts concerning the reliability of (Zhu et al., 2022)'s model development and validation, and the authors are hence invited to placate these concerns in their reply.