Jams and Cakes: A Closer Look on Well Clogging Mechanisms in Microscale Produced Water ReInjection Experiments

We present a new experimental approach to further understand the injectivity impairment due to reinjection of produced water in an oilfield, containing residual oil and solids. A unique microfluidic setup with imposed flowrate is characterized by excellent reproducibility and allows one to determine the kinetics of external cake formation and the propagation of the damage inside the porous medium, similar to what happens at the injection wellbore. The growth rates of the external cake and that of the propagation of the internal damage exhibit discontinuities, likely related to a pressure buildup up to a threshold Laplace pressure above which the O/W Pickering droplets are pushed through, and which sets a limit to the cake growth. Finally, the external cake reaches a quasi-stationary thickness whose mechanisms are discussed below. Direct visualization readily achieved in microfluidic experiments, coupled with spatiotemporal image analysis, enables better spatial resolution than core flooding experiments and shows that the damage occurs in a small region close to the entry to the porous medium. These developments lead to the derivation of an analytical model of the damage formation. It appears that although very localized, this damage strongly decreases the global permeability of the whole porous medium. Finally, controlled temperature experiments permit to identify the variation of the viscosity of the oil droplets (or the viscosity ratio), as the primary mechanism by which temperature influences clogging. Clogging is slowed at high temperatures, but the final state is characterized by particle clogging and is thus irreversible.