This work aims at evaluating a new surfactant based viscoelastic fluid for Chemical EOR applications. The surfactant based fluid exhibits a viscous phase at low concentration and high temperature, useful for improving oil recovery.

The viscoelastic fluid is induced by wormlike micelles formed by self-assembled surfactants. The phase diagram of the surfactant in pure water was established using a pervaporation-based microfluidic device (Leng et al., PRL, 96, 2006). Isotropic wormlike micelles have been observed up to 12 % w/w. In a second step, Particle Tracking Microrheology (PTM) was used to investigate the rheological properties of the fluid for surfactant concentrations below 2% w/w in water. Viscosity at low surfactant concentrations (0.1% to 0.3 % w/w), T= 80°C, in synthetic sea water (3.9 % w/w TDS) and in sodium chloride (2 % w/w TDS) has been recorded. Data shows that the viscosity is weakly dependent on brine concentration and evolves between 3 and 15 mPa.s (γ=10 s-1), for surfactant concentrations between respectively 0.1% to 0.3 % w/w.

The second series of tests consisted of core-flood experiments at 80°C in Clashach sandstone with brine solution (NaCl 2% w/w) containing surfactant concentrations between 0.1 %w/w and 0.3 %w/w. The surfactant is shown to adsorb moderately on the sandstone (50 μg/g) and displace a great fraction of residual oil (from Sor=0.49 to Sor=0.20).

These preliminary results show a strong potential for this new surfactant based viscoelastic fluid in chemical EOR. Compared to other viscoelastic fluids this product shows the following advantages:

Superior viscosity, at low surfactant concentration, in hard brine and at high temperature Better displacement of residual oil in core-flood with moderate adsorption

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