Microemulsion and phase behavior properties of (Dimeric ammonium surfactant salt – heavy crude oil – connate water) system

• At low concentration (≤ 0.25 wt.%), an ultra-low interfacial tension (order of 10−3 mN/m) was achieved for the candidate heavy oils.
• Interfacial tension (IFT), dependent of reservoir environment, increased linearly with formation temperature.
• The presence of metal divalent ions and chemical composition of the crude oil were found to alter heavy oil solubilization.
• Cationic dimeric micellar slugs exhibited a low adsorption on reservoir formation rocks.
• Investigated slugs mitigated formation of acidic materials generated as coproduct during other recovery processes.

Fundamentally, recovery methods of untapped crude oils require injection of foreign material(s) in the reservoir, which subsequently promote(s) the displacement of residual oil. In chemical enhanced oil recovery (EOR), the microscopic sweep efficiency depends primarily on achievement of a low interfacial tension. The present work investigates into the surface tension and phase behavior properties of microemulsion developed from a contact between a dimeric ammonium salt surfactant achieve an ultra-low interfacial tension (IFT) was compared with a conventional polysorbate surfactant commonly used in chemical EOR. At fairly low concentration, dimeric surfactants achieved an IFT of order of 10−3 mN/m. Salinity tolerance and IFT were significantly altered not only by the heaviness i.e. API of the crude, but also by the reservoir conditions. Moreover, alkane carbon number (ACN), introduced in this work, revealed that modeling a micellar slug formulation solely based on chemical composition of the crude and/or its nature could be misleading. Presence of divalent ions was found to promote the increase in IFT rather to a shift to a lower value. Also, a relative low adsorption of micellar slug was found in both dolomite and Berea sandstone. However, active head of the dimeric surfactant showed a preferential attachment to carbonate rock while low interactions were observed for sandstone. Lastly, the present study has highlighted an inhibiting acidity activity for dimeric ammoniums salt surfactants.