Water level and mobilisation of colloids in porous media

•It is practically impossible to remove 2 μm charged colloids from a dry porous media.•Nearly desalinated water is needed to mobilise particles in saturated media.•A gradual increase in water level is key for mobilisation in unsaturated media.•The proposed model can be used to forecast a potential well clogging. Unforeseen clogging and low well productivity during exploitation of oil and gas reservoirs result from a mobilisation of densely deposited particles. The proposed model predicts the mobilisation in unsaturated porous media based on the changes in water level, and hydrophilicity and size of mobilisable particles. Domains of particle attachment, sliding, rolling, and lifting were found from a phase diagram based on a mechanical equilibrium. The degree of mobilisation was correlated with experimental data through a maximum retention function. The validity of the proposed model was confirmed by a close match of theoretical predictions with results of 46 laboratory tests on particle detachment. Our analysis shows that it is practically impossible to remove 2 μm charged colloids from a dry porous media. Nearly desalinated water with ionic strength of 0.001 M or less are needed to mobilise particles in saturated media at typical groundwater conditions. A gradual increase in water level is key for mobilisation in unsaturated media. The proposed model can be used to forecast a potential well clogging.