PWRI-Induced Injectivity Decline: New Insights on In-Depth Particle Deposition Mechanisms

摘要

Injectivity decline during PWRI originates not only from filter-cake build-up, but also from in-depth deposition of oil droplets or solid particles. Physical modelling of particle deposition mechanisms in porous media is thus of key interest for optimizing PWRI operations. The present work brings new insights on oil droplets and solid particle deposition mechanisms in porous media. The experimental conditions were selected such as 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 non-dimensional form the impact of both flow rate and particle size. The results are analysed in the frame of the "colloidal approach". For oil droplets and solid particles, the deposition efficiency (η) shows a transition from a behaviour in which η varies as a power-law of Peg, with exponent values -2/3 (Diffusion Limited Deposition, DLD) to -1 (Reaction Limited Deposition, RLD), characteristic of convection-diffusion regime, to a behaviour characterized by an increase of η versus Peg, characteristic of hydrodynamic deposition regime. In the case of oil droplets (not or slightly charged), the transition occurs at a critical Peg value,geom_C~Peg , corresponding to a diffusion layer thickness around the collector grain equal to the droplets diameter. In the case of electro-sterically stabilized solid particles, the transition takes place at Peg_CPeg_C~geom for larger particles.