Dual-fractal nuclear magnetic resonance to relative permeability conversion: A novel framework for multiphase flow characterization

Based on dual-fractal theory, this paper proposes a novel methodology to transform nuclear magnetic resonance (NMR) measurements into relative permeability model, thereby realized the challenge of accurately quantifying multiphase fluid flow in dual-fractal porous media. The novel relative permeability model integrates a multitude of parameters associated with the microscopic pore architecture of porous media. It can be verified through case studies that the newly constructed relative permeability model demonstrates excellent applicability. Furthermore, we have discovered a correlation between the segmentation characteristics of the relationship between the pore radius (r) and transverse relaxation time (T2) in low-permeability sandstone reservoirs and the number of peaks in the NMR curve. Specifically, the single-peak type can usually be divided into two segments, while the multi-peak type can generally be divided into three segments. The comprehensive fractal dimension (Dc) derived from the weighting method effectively captures the holistic core heterogeneity. The characteristics of small diameter pores are particularly sensitive to variations in the pore tortuosity fractal dimension (Dτ), the pore structure fractal dimension (Df), Dc, and ε (represents the pore size ratios). Given that the wetting phase preferentially occupies small pores, its relative permeability is significantly affected by these parameter changes. Conversely, the non-wetting phase mainly flows through large pores and is thus less influenced by changes in these parameters.