Synergistic Mechanism of Hydrolyzed Polyacrylamide Enhanced Branched-Preformed Particle Gel for Enhanced Oil Recovery in Mature Oilfields

Branched-preformed particle gel (B-PPG) is a novel agent for EOR application in mature reservoirs. To improve the enhanced oil recovery (EOR) performance of B-PPG, the heterogeneous combination flooding system composed of B-PPG, hydrolyzed polyacrylamide (HPAM), and surfactant was proposed. However, the synergistic mechanism of B-PPG and HPAM still remains unclear. Here, a series of experiments were performed to study the viscosities of HPAM, B-PPG, and mixture of HPAM and B-PPG, evaluate the suspension stability of B-PPG and mixture of HPAM and B-PPG, to investigate the propagation behavior of HPAM, B-PPG, and a mixture of HPAM and B-PPG through porous media, and to study the EOR performance of HPAM, B-PPG, and a mixture of HPAM and B-PPG in heterogeneous reservoirs by performing parallel sand pack flooding experiments. Results show that the suspension stability of B-PPG can be improved by adding polymer due to the increase in viscosity. The higher the HPAM concentration is, the higher viscosity of mixture of HPAM and B-PPG suspension and the better the suspension stability is. Due to the lubrication and increased viscosity effect of the polymer, compared with the B-PPG suspension, the HPAM enhanced B-PPG suspension can be more easily injected into the porous media and can propagate through porous media. The propagation behavior of HPAM enhanced B-PPG through porous media is achieved by blocking, deforming, and passing through the pore throat. EOR performance results in a heterogeneous reservoir demonstrate that HPAM enhanced B-PPG flooding shows better sweep efficiency improvement ability and recovers more remaining oil left unswept in the low permeability zones.