Summary Many operations involve the injection of fluids into the formation around a well. In many cases, the fluids contain colloidal particles, either initially present or introduced during the operation through dirt or naturally occurring particles. Therefore, all injection schemes potentially suffer from injectivity decline. This injectivity decline is caused by clogging of the formation by particles, forming an external filter cake on the surface of the formation and blocking the pores inside the formation. This paper reports on the effects of gas on the injectivity of particles in sandstone. Experiments were performed in which water containing micron-sized particles (hematite) was injected into sandstone cores with or without small gas bubbles (nitrogen) present in the water. The position and amount of particle deposition could be determined both visually and by chemical analysis. It was found that the presence of gas reduces the external filter cake formed on the inlet surface of the core. Also, with gas, the particles penetrate deeper inside the core and more particles pass through the core and are detected in the effluent stream. The same effects are enhanced when the mixture of gas bubbles and water is replaced by foam. This suggests that the presence of gas/water interfaces has a major influence on the retention of particles in the sandstone. Possible mechanisms are discussed. The pressure drop across the core when gas or foam is present is initially higher than in an identical test without gas because of relative permeability effects or foam-flow resistance. However, because fewer particles are retained, ultimately the pressure drop is significantly less when gas is present. This effect may be significant in injection operations involving foam and offers ways to mitigate injectivity loss.

Many operations involve the injection of fluids into the formation around a well. In many cases, the fluids contain colloidal particles, either initially present or introduced during the operation through dirt or naturally-occurring particles. Therefore, all injection schemes potentially suffer from injectivity decline. This injectivity decline is caused by clogging of the formation by particles, forming an external filter cake on the surface of the formation and blocking the pores inside the formation. This paper reports on the effects of gas on the injectivity of particles in sandstone. Experiments were performed in which water containing micron-sized particles (hematite) was injected into sandstone cores with or without small gas bubbles (nitrogen) present in the water. The position and amount of particle deposition could be determined both visually and by chemical analysis. It was found that the presence of gas reduces the external filter cake formed on the inlet surface of the core. Also, with gas, the particles penetrate deeper inside the core, and more particles pass right through the core and are detected in the effluent stream. The same effects are enhanced when the mixture of gas bubbles and water is replaced by a foam. This suggests that the presence of gas/water interfaces has a major influence on the retention of particles in the sandstone. Possible mechanisms are discussed. The pressure drop across the core, when gas or foam is present, is initially higher than in an identical test without gas, because of relative permeability effects or foam flow resistance. But since fewer particles are retained, ultimately the pressure drop is significantly less when gas is present. This effect may be significant in injection operations involving foam and offers ways to mitigate injectivity loss. Introduction The worldwide production of water during hydrocarbon production is on average 75% of the produced fluids. Physical and chemical properties of the produced water mainly depend on geographical location, geological formation, and type of hydrocarbons. Handling of produced water is one of the main issues in petroleum industry as it contains residual hydrocarbons, heavy metals, radionuclide, numerous inorganic species, suspended solids and chemicals used in treatment and hydrocarbon extraction. The required facilities and equipment for treatment of the produced water are expensive. The development of new technologies to minimize the production of water and consequently the costs of water treatment and looking for ways that existing facilities can handle larger volumes of water is a big challenge for oil companies. One of the most economical and environmentally friendly methods to dispose of produced water is to inject it into a suitable subsurface formation. Water injection into a reservoir can be beneficial because it helps maintain reservoir pressure and improve oil recovery.