The Influence of Surface Properties on the Retention and Mobilization of Silica Particles in a Porous Network Investigated by Microfluidic Methods

Produced water re-injection (PWRI) is the water management strategy with least environmental impact during petroleum recovery. A major challenge, however, is clogging of pores in the injection reservoir by particles suspended in the produced water. Basic understanding of transport and retention of particles in porous media is required to better handle this injectivity decline. Here, a microfluidic technique was used to study the transport and retention of monodisperse silica particles in a porous network. The amount of particle retained in the network, the distribution of the particles in the network and the aggregation state of the particles depended on particle–particle and particle–pore wall interactions. These interactions were modulated by varying the salinity of the suspension introduced into the network and by adsorbing surface-active additives (a non-ionic surfactant, a cationic flocculant and an anionic flocculant) onto the particles. The latter was done to mimic how adsorption of production chemicals onto solid particles in produced water influence their transport in reservoirs. In accordance with the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory, high-energy barriers prevented both aggregation of particles and retention of particles in the pore network at low salinities. A threshold salinity was reached, where the energy barriers were reduced so that individual particles were retained in the pore network. Further increase in the salinity resulted in aggregation of particles prior to the network and most of the aggregates were accumulated close the entrance of the network. Adsorption of a non-ionic surfactant provided sufficient steric hindrance to prevent aggregation of particles at high salinities, and the retention of particles became more evenly distributed in the network. The adsorption of the anionic flocculant resulted in steric hindrances that reduced the retention of particles in the network, while the opposite was seen when the cationic flocculant was adsorbed onto the particles. The extent of re-mobilization of retained particles indicated the strength of the particle–pore wall interactions.