Filling the Empirical Gap: Relative Permeability Upscaling Methods for Heterogeneous Tidal Channel Sand Reservoirs in the Eastern Niger Delta Margin

Relative permeability upscaling from core-scale to simulation-scale is a critical but poorly resolved problem in heterogeneous tidal channel sand reservoirs, where sedimentary heterogeneity at sub-metre scales fundamentally controls displacement behaviour at the production well scale. This study addresses the empirical gap in relative permeability upscaling methodology specifically for tidal channel sand reservoirs of the eastern Niger Delta margin. Tidal channel reservoir core intervals from two wells in eastern Niger Delta OMLs were described at millimetre resolution using core photography and micro-CT scanning to identify and quantify heterogeneity elements including reactivation surfaces, tidal bundles, and mud drapes. Two-phase relative permeability experiments were conducted on 48 core plugs representing the identified heterogeneity elements, providing a facies-specific relative permeability dataset. Four upscaling methods were evaluated: single-phase arithmetic averaging, pore network modelling, flow-based numerical upscaling using fine-grid simulation, and pseudo-relative permeability generation by history matching on a fine-scale heterogeneous model. Flow-based numerical upscaling produced pseudofunctions that reproduced fine-scale displacement behaviour with a fractional flow curve match accuracy superior to all other methods, reducing the mean fractional flow prediction error from 9.1 percent for arithmetic averaging to 1.8 percent. The upscaled pseudofunctions exhibit strong directional anisotropy, with the cross-bedding perpendicular direction showing significantly higher fractional flow breakthrough compared to the parallel direction. Keywords: relative permeability upscaling, tidal channel sand, Niger Delta, reservoir heterogeneity, pseudofunction.