The Generation, Stabilization and Migration Rules of Crude Oil Emulsion During the Process of Amphiphilic Polymer Flooding

摘要

It has been proven by field tests that crude oil recovery could be enhanced with the generation of stable emulsions. Amphiphilic polymers display better capability in emulsifying crude oil as compared with that of traditional polymers attributing to the co-existence of hydrophilic and hydrophobic groups in molecular chains. To investigate the generation of emulsified oil droplets with the hydrophobically modified polyacrylamide (HMPAM) in reservoirs, porous mesh shearing method to generate emulsions was first conducted. The stabilization mechanism was then elucidated by comparing properties of emulsions which are stabilized by HMPAM with different degree of β-cyclodextrin (β-CD) inclusion. The flow behavior of various HMPAM emulsions was further evaluated by rheological method and comparative seepage experiments. The results show that the snapping action of residual oil and the shearing action of HMPAM solution in porous media are the main reasons of the generation of emulsions, the emulsifying property of which is mainly affected by the concentration of HMPAM, injection rate, migration distance as well as the average diameter of pore throats. β-CD could mask hydrophobic groups on HMPAM molecules because of the host-guest interaction, resulting in a transition of corresponding polymer emulsion from stable state to unstable one. Over 80% reduction in stability index is observed after inclusion for the emulsion with polymer concentration above the critical aggregation concentration, indicating that the presence of hydrophobic groups is the most important source of emulsifying and stabilizing capability of HMPAM. Furthermore, the viscoelasticity of the emulsion system is enhanced by the synergistic effect of supramolecular networks and emulsified oil droplet. During its transport through porous media, the polymer emulsion shows high flow resistance and its injection pressure exhibits an obviously creeping fluctuation increasing phenomenon as compared to surfactant emulsion and sheared polymer solution.