Effect Of Polymer Solution Structure On Seepage Characteristics

To meet the requirement for polymer flooding agent under different reservoir environment, home and abroad scholars had developed several kinds of polymers with the temperature-tolerance and salt-resisting properties. In the polymer solution, with the effect of solution environment, the changes of molecular conformation and solution structure would induce the changes of solution properties and compatibility between molecular structure and reservoir. So, for providing foundation for the R&D of polymer flooding agent which is fit for HT/HS reservoir, on the basis of solution structure, researching the relation between molecular conformation and solution properties, discussing the matching between solution structure and porous media.Selected two kinds of polymer with different molecular conformation as the research objects, the first one, ultra-high molecular weight partially hydrolyzed polyacrylamide (HPAM), which is the representative linear structure polymer; the second one, hydrophobically associating water-soluble polymer (HAWP), is a typical linear structure polymer with special structural group on the side chains. In the solution, with the increase of polymer concentration, the entanglement of HPAM molecule was enhanced, and would form packed solution structure with the different intensive degree. For the HAWP, the entanglement of molecular coils and hydrophobical association were strengthened gradually, and formed3-D network structure.For the packed solution structure formed mainly by entanglement action, the high salinity and shear action would weaken the entanglement among molecules, decrease molecular coils dimension, and result in remarkable decrease of packed intensive degree. On the other hand, for the solution with network structure formed mainly by hydrophobical association and molecular coils entanglement, the hostile reservoir conditions would cause curl and crack of molecular chains, weaken association, but the solution still presented network structure, although the structure was a little weaker.In the porous media, the adsorption of polymer solution with packed structure on the rock surface presented monolayer adsorption characteristic. When polymer molecular coils passed through the pore throat, the additional resistance caused by stretching action would rise with the increase of flow velocity, and accompanied with ascending flow resistance. The adsorption of polymer solution with network structure on the rock surface presented layer-by-layer adsorption characteristic; the resistance factor and residual resistance factor descended with the incremental flow velocity. These laboratory findings evidenced that the seepage characteristics of polymer solution with packed structure were depended on the matching between molecular coils dimensions and porous media, and the seepage characteristics of polymer solution with network structure were rested with intermolecular interactions, of which the reversibility enhanced the mobility control ability of polymer solution, and ensured the favorable injectivity and propagation characteristics in the porous media.In the high permeability and heterogeneous reservoir, it is an ideal way to enhance mobility control ability of polymer solution by extending the macromolecule dimension and strengthening the intermolecular interactions. While, in order to gain well injectivity and propagation characteristics in the low permeability porous media, the molecular weight and intermolecular interactions should be decreased to a moderate degree.