A flow simulation method based on digital rock analysis in multi-layer heterogeneous reservoir

Conventional multi-tube parallel-flooding experiments and single-/double-layer pore network models are insufficient to characterize interlayer interference and microscopic residual oil distribution in thin interbedded heterogeneous reservoirs. This study constructs a triple permeability combined pore network framework from micro-computed tomography (micro-CT) digital rocks. Three digital rock models for high, medium and low permeability fluvial sandstone rhythmic layers are obtained via micro CT scanning and Otsu threshold segmentation, each satisfying Representative Elementary Volume (REV) criteria at 1.2 mm × 0.8 mm × 0.8 mm. Vertically connected three layer digital rock assemblies are built for invasion percolation based quasi steady state two phase imbibition drainage simulation. With a permeability ratio of ~ 3 across layers, permeability is jointly controlled by pore throat size and coordination number, leading to non monotonic variation between mean pore radius and bulk permeability. Reduced permeability narrows the oil water co flow interval; intensified capillary trapping in fine throats dominates this effect, and weakened pore connectivity plays a secondary role. Imbibition exhibits staged flow behaviors: water first occupies large conduits in medium/high permeability layers at low water saturation, and later invades fine pores in low permeability layers, generating layered feature relative permeability curves. Preferential flow occurs in medium and high permeability zones, while irreducible water and residual oil mainly reside in low permeability strata. Under the given permeability contrast, it preliminarily reveals the pore scale control trends of permeability gradients on capillary characteristics and relative permeability evolution. It can provide a microscale simulation reference for waterflooding development of thin interbedded heterogeneous reservoirs. Note that this simulation adopts idealized pore network simplifications under one fixed permeability contrast and mixed wet condition.