Reactive Pore Network Modeling Dedicated to the Determination of the Petrophysical Property Changes while Injecting CO2

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Abstract A Pore Network Model is an efficient tool to account for phenomena occurring at the pore scale. Its explicit threedimensional network of pores interconnected by throats enables to easily consider the topology and geometry effects on upscaled and homogenized petrophysical parameters. In particular, this modeling approach is appropriate to study the rock/fluid interactions. It can provide quantitative information both on the effective transport property modifications due to the reactions and on the structure evolution resulting from dissolution/precipitation mechanisms. The developed model is based on the resolution of the macroscopic reactive transport equation between the nodes of the network. By upscaling the results, we have then determined the effective transport properties at the core-scale. A sensitivity study on reactive and flow regimes has been conducted in the case of single-phase flow in the limit of long times. It has been observed that the mean reactive solute velocity and dispersion can vary up to one order of magnitude compared to the tracer values because of the concentration profile heterogeneity at the pore scale resulting from the surface reactions. As for the reactive apparent coefficient, when the kinetics is limited by the mass transfer, it can decrease by several orders of magnitude with regard to the one calculated by the usual perfect mixing assumption. That is why scale factors should be added to the classical macroscopic transport equation implemented in reservoir simulator to accurately predict the reactive flow impacts. For each study case we have also obtained the permeability variation versus the porosity evolution in a physical way which accounts for reactive transport conditions. It appears that the wall deformation pattern and its impact on petrophysical properties must be explained by considering both microscopic and macroscopic scales of the reactive transport, each one governed by a dimensionless number comparing reaction and transport characteristic times. This work contributes to improve the understanding of surface reactions impacts on reactive flow in one hand, and on permeability and porosity modifications in the other hand. Using the PNM approach, scale factors parameters and permeability versus porosity relations can be determined for various rock-types and reactive flow regimes. Once integrated as inputs in a reservoir simulator, these relations are a powerful and convenient means to enhance the modelling accuracy of the petrophysical properties evolution during a reactive fluid injection such as CO2-rich brines.