EFFECT OF WETTABILITY ON THE PETROPHYSICAL PARAMETERS OF VUGGY CARBONATES: NETWORK MODELING INVESTIGATION

Abstract

Carbonate rocks often present bimodal pore size distributions usually attributed to the presence of vugs that can communicate through the matrix (separated vugs) or form an interconnected pore system (touching vugs). Due to these different degrees of interconnectivity, vugs and matrix may have different wettability, with the matrix being usually water-wet and the vugs oil-wet. These wettability heterogeneities and connectivity regimes infer to the porous medium petrophysical properties that may vary within a wide range of values. The objective of the present work is to demonstrate the effect of pore-scale wettability heterogeneities on effective capillary pressure and relative permeability values of vuggy structures. To this end a pore network numerical simulator is used, that calculates multiphase flow properties taking into account the bimodal pore structure specificity and the fractional wettability. The complex real pore space is represented as a dual-network model that incorporates information on the primary (matrix) and the secondary (vugs, fractures) porosity and accounts for the connectivity of the secondary porosity. The model permits to impose heterogeneous wettability by assigning different water/oil contact angles according to the desired heterogeneity pattern. In water/oil displacements, drainage and imbibition mechanisms occur simultaneously according to the local wettability.