To investigate the relationship between the flow behavior and microdisplacement performance and the molecular structures, especially associating monomer content, of hydrophobically modified partially hydrolyzed polyacrylamides (HMHPAMs) with varied associating monomer content, compared with that of partially hydrolyzed polyacrylamide (HPAM), a series of experiments were conducted that involved the filtration through screen viscometer, nucleopore membrane, and series-connection microporous membranes; the flow through three serial mounted artificial cores; and the displacement in the microetching model. The screen factors and the hydrodynamic sizes of polymers were obtained by screen viscometer and nucleopore membrane, respectively. The results show that the screen factors and hydrodynamic sizes of HMHPAMs were much-more sensitive to the polymer concentration, filtration pressure, and associating monomer content than HPAM. Moreover, the filtration experiment through series-connection microporous membranes indicates that there were moderate associating monomer content or greater flow pressure or pore size for HMHPAMs to easily pass and obtain equivalent differential pressure between membranes, which implies that the compatibility between the pore size and the hydrodynamic sizes of the microstructures is the most-important factor for the injectivity of HMHPAMs. The resistance factor (RF) established by HMHPAMs through three serial mounted artificial cores notably tended to be higher than HPAMs, and the HMHPAMs with higher associating monomer content could generate a greater RF. In contrast, when the associating monomer content was low enough and the permeability was high enough, the flow could obtain equilibrium easily and the RFs were almost in accordance, which indicate there was moderate associating monomer content for HMHPAMs to propagate deep into the cores. At the same viscosity, HMHPAMs had better microdisplacement efficiency than glycerol (no effect) and HPAM (a small portion) for displacing the residual oil trapped in the “dead” ends of flow channel. The pilot tests of the associative polymer AP-P4, which was developed for Bohai oil fields, have demonstrated the great application potential of HMHPAMs for enhanced oil recovery (EOR).

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