Visual investigation of simultaneous clay swelling and migration mechanisms and formation damage consequences using micromodels

One of the most important constituents of oil and gas reservoirs is clay minerals; they may cause formation damage by swelling and migration. When water with lower salinity than formation water invades clay-rich porous media, the clays absorb the water, which results in swelling and, therefore, limit the available space for fluids to flow. Clays may also detach from rock surfaces and start to migrate and block pore throats. Both mechanisms lead to permeability impairment as a critical formation damage element. A better understanding of damage due to clays helps us to control and overcome the problem, which affects oil recovery. In this work, the swelling and migration of clays are studied at the pore scale using clay coated micromodels. The effect of the composition and salinity of injected brines on sodium bentonite swelling and migration were visualized, investigated, and analyzed by a novel approach based on an image processing technique. The effect of simultaneous clay swelling and migration on porosity alteration at different sections of the micromodel was studied to estimate damage, qualitatively and quantitatively. Our experiments showed that the presence of KCl salt in the brine used in drilling, completion, and development operations is vital to control formation damage. The best damage remedy performance was reached when a salt with small hydrated radius cations, such as KCl is combined with a salt with divalent and small hydrated radius cations, such as CaCl₂. The combination of KCl and CaCl₂ showed only 2.8% reduction of porosity, while KCl showed around 7% reduction of porosity. In migration control, KCl showed the best ability to control migration and most of the migrated clays were re-adsorbed in the porous media.