Behavior of a Scale Inhibitor Water-in-Oil Emulsion in Porous Media

Abstract

Summary The use of water-in-oil emulsions (WO) to deploy scale inhibitors has been reported in the literature as an alternative to water-based squeeze treatments. The non-aqueous nature of these emulsions has the advantage of preventing water blocking, which adversely affects oil production in aqueous squeeze treatments. Placing the scale inhibitor in a WO or "invert" emulsion has shown in some cases the additional advantage of enhancing treatment lifetime. However, results from the literature seem contradictory and highlight a poor understanding of this technology. The present paper aims at providing further insight on emulsified scale inhibitor placement in porous media. We focus on studying the retention mechanisms of the emulsion droplets containing the scale inhibitor (SI), whilst SI release and, consequently, the performance of the emulsified squeeze is not discussed. Preliminary experiments were conducted using a low molecular-weight biopolymer as a SI. They evidenced a low adsorption/retention of this SI in aqueous solution. Reformulation of the product under invert emulsion was investigated to measure inhibitor retention. Results from coreflood experiments using well-characterized silicon carbide (SiC) packs provided preliminary evidence of aqueous droplet adsorption as the main retention mechanism in porous media. This was expected considering the average droplet size of 0.3 µm (300 nm). The mother formulation of the WO emulsion is a concentrate, containing 80% of water phase and 8% of active SI. The product can be diluted down to 2% water phase by adding the desired oil phase. Dilution does not affect emulsion stability or increase the emulsion's droplet size. These results represent a promising first step towards the development of a technically and commercially viable, environment-friendly SI technology based on WO emulsions. Future work to study the emulsified SI release mechanisms and its consequent performance are being prepared to compare with conventional aqueous squeeze treatments.