Synthesis of new PPG and study of heterogeneous combination flooding systems

Abstract

For the problem wherein a reservoir demonstrates strong heterogeneity after polymer flooding and the conventional oil displacement method cannot effectively displace the oil in the low-permeability layer, preformed particle gel (PPG) is synthesized and forms a heterogeneous composite oil displacement system with a weak-base alkali–surfactant–polymer (ASP) system. The core flow and oil displacement experiments were conducted to test the PPG performance. The injection parameters of the heterogeneous system were optimized, and the oil displacement effect was evaluated. Results show that the best synthesis parameters of PPG are as follows – 25% acrylamide, 25% degree of hydrolysis, 1.5 × 10–3 g of cross-linking agent, and 2.25 × 10–2 g of initiator. PPG can swell slowly and has good salt and temperature resistance; the particles with different particle sizes have good elasticity and strength after complete expansion, and they have good compatibility with cores having different permeability values. Compared with the weak-base ASP system, the heterogeneous system can maintain interfacial tension on the order of 10–3mN/m when the concentrations of the alkali and the surfactant are low. The heterogeneous system can (i) achieve adaptive sealing of the formation owing to its good deformation recovery ability, (ii) play the role of liquid flow steering, (iii) adjust the water absorption profile, and (iv) improve heterogeneity. The optimal component concentration of the heterogeneous system is 500 mg/L PPG, 1400 mg/L polymer, 0.3% petroleum sulfonate, and 1.2% sodium carbonate, the best injection method being one wherein a heterogeneous system and a weak-base ASP system are injected alternately.