Injectivity Decline From Produced-Water Reinjection: New Insights on In-Depth Particle-Deposition Mechanisms

Abstract

Summary Injectivity decline during produced-water reinjection (PWRI) originates not only from filter-cake buildup but also from in-depth deposition of oil droplets or solid particles. Physical modeling of particle-deposition mechanisms in porous media is thus of key interest for optimizing PWRI operations. The present work brings new insights on oil-droplet and solid-particle-deposition mechanisms in porous media. The experimental conditions were selected such that the ratio between pores and particle sizes is sufficiently large to ensure in-depth propagation. The parameters are the nature of the particles injected and a Peclet number calculated on the size of the collector grains (Peg) that encompasses in a nondimensional form the impact of both the flow rate and the particle size. The results are analyzed within the framework of the "colloidal approach." For oil droplets and solid particles, the collection efficiency (η) shows a transition from a behavior in which η varies as a power law of Peg, with exponent values −⅔ [(diffusion-limited deposition (DLD)] to −1 [reaction-limited deposition (RLD)] that are typical of the convection/diffusion regime, to a behavior characterized by an increase of η vs. Peg, typical of the hydrodynamic deposition regime. In the case of oil droplets (slightly charged), the transition occurs at a critical Peg value, PegC≈PegCgeom/10, corresponding to a diffusion-layer thickness around the collector grain of the same order of magnitude as the droplet diameter. In the case of electrosterically stabilized solid particles, the transition takes place at PegC≪PegCgeom for small particles and at PegC>PegCgeom for larger particles.