Pilot test of polymer microsphere alternate surfactant flood (PMAS) with mixtures of anionic-cationic surfactants under harsh conditions in a sandstone reservoir

The first pilot test of polyacrylamide microsphere alternate surfactant flood (PMAS) with mixtures of anionic-cationic surfactants (S_a/c) was carried out for a high-temperature, high-salinity, and high-hardness sandstone reservoir to demonstrate the potential of this novel technique to improve oil recovery. A critical micelle concentration (CMC) of 4.82 mg/L, an ultralow interfacial tension (IFT) of 8 × 10⁻⁴ mN/m, and a high oil solubilization of 22 were obtained. Static and dynamic adsorptions of S_a/c on natural core containing 15 wt% clay were reduced to about 2.20 and 0.30 mg/g-core, respectively, with the addition of adsorption inhibitor (AI). Since June 2014, the pilot test of PMAS was carried out in a Sinopec reservoir with a temperature of 87 °C, a salinity of 260,393 mg/L, and a hardness of 6,401 mg/L. Twelve cycles of alternative injection of 0.0125 PV S_a/c with a concentration of 0.1% and 0.0125 PV polyacrylamide microsphere with a concentration of 0.2% were conducted at an injection rate of 0.1 PV/yr, for a total of 0.3 PV chemical injection. As a result, the net daily oil production increased from 0 t to 6.5 t, and the water cut decreased from 96.3% to 93.8%, leading to an ultimate improved oil recovery of 6.3% original oil-in-place.