Emulsions in porous media from the perspective of produced water re-injection – A review

Abstract

During offshore production, it is typical to discharge produced water into the sea after treating it to a level that meets environmental regulations. A growth in the volumes of produced water and increasingly stringent requirements have drawn attention to re-injection of produced water as a more viable disposal method. Produced water re-injection is regarded as an environmentally friendly and cost-efficient approach that allows integration of produced water with reservoir management. However, loss of injectivity, due to the plugging of pores by oil droplets and particles present in produced water, limits implementation of re-injection. This review discusses engineering challenges during re-injection and summarizes the knowledge and the gaps in the literature on the permeability reduction due to the flow of dilute oil-in-water emulsions. First, a short introduction into the origins of produced water, its composition, and the treatment techniques employed offshore are provided. An overview of the water injection strategies as well as a discussion of the past field experience of produced water re-injection is given. This is followed by a detailed review of the flow of diluted oil-in-water emulsions through porous media from the permeability reduction perspective. An overview of models for predicting permeability reduction during the flow of emulsions is provided. The physical parameters affecting the droplet retention and physicochemical interactions between droplets and pore walls are discussed. The studies that investigated co-injection of oil droplets and solid particles are included as well. The review identified that the effect of droplet stability, oil viscosity, wettability, and particles on droplet retention is not sufficiently examined. It was found that drop-to-pore size ratio is a crucial factor for droplet retention, but it is often omitted in the industry. An outlook on the gaps and suggestions to address them was provided. Microfluidics was pointed out as a complementary technique to coreflooding.