Separation of SAGD produced emulsions through a combined pre-dewatering and demulsification process

Abstract

In this paper, we proposed a combined pre-dewatering and demulsification process to investigate its effectiveness in separating produced emulsions from the stream-assisted gravity drainage (SAGD) operation. Five demulsifiers (synthesized by polymerization of the polycyclic phenol-amine resin, polyoxyethylene and polyoxypropylene) and six polyamine block polyether reverse demulsifiers were prepared and evaluated through laboratory bottle tests and field tests. The effects of chemical properties (resin and asphaltene contents and molecular weight), injection dosage, injection scheme (demulsifier only versus the combined demulsifier and reverse demulsifier), and treatment density on separation efficiency were addressed. Results indicate that, in the pre-treatment stage, the polyamine block polyether reverse demulsifiers were able to migrate to the oil-water interface promptly, replace the pre-existing natural surfactants, weaken the strength of interface film, partially neutralize surface charges, and promote the coalescence and separation of water droplets; the emulsion type was transitioned from oil-in-water (O/W) to water-in-oil (W/O) after treatment. In the subsequent demulsification process, the following injected high-temperature resistant demulsifier separated the W/O emulsion with multiple effects. The asphaltene dispersant and clay/sand removing additive blended into the demulsifier strengthened the separation performance by weakening the stability of emulsions and reducing the surface activity of clay particles. Compared to the demulsifier only injection scheme, the synergistic effect delivered by the combined chemicals expedited oil and water separation. The field test results exhibited that the selected chemicals could efficiently treat the SAGD produced emulsions, reflected by a more stable density profile, lower oil content of the separated water, and lower water content of the separated oil.