Heterogeneity control ability in porous media: Associative polymer versus HPAM

In chemical EOR (especially polymer flooding), the swept area and oil recovery of displacing fluids were strongly affected by reservoir heterogeneity. To qualitatively study and discuss the oil reservoir heterogeneity control capacity of a new water-soluble polymer, associative polymer (AP-X), this work, compared with HPAM, conducted a series of laboratory experiments involving apparent viscosity, fluorescence, rheological properties, threshold pressure, flow and transport in porous media, as well as the oil micro-/macro-displacements in interstratified connected and parallel heterogenous micro-/macro-models. The results showed that AP-X had more significant thickening capacity and viscoelasticity than HPAM and presented noticeable self-association effect due to the associative interaction between hydrophobic groups. To enter into the porous media with the same or higher permeability, AP-X needed much greater injection (threshold) pressure than HPAM although the threshold pressure of AP-X significantly decreased as increasing permeability. More importantly, AP-X could not only present a good conductivity but also establish significantly higher flow resistance. In addition, at a greater permeability contrast of 8 times (8000/1000 mD), AP-X mainly swept the high permeable layer and slightly swept the low permeable layer slowly within 0.5 PV, which was accompanied by the significant sweep for the low layer after 0.5 PV. More interestingly, AP-X could also make the fluid diversion of the post-water to further mobilize the oil in low permeable layer and obtain a higher EOR than HPAM. All results indicate that associative polymer has remarkable application potential and advantages than HPAM in EOR not only regarding to better thickening property and viscoelasticity but also involving higher flow resistance and significant heterogeneity control capacity, which can provide a new system design concept and technical ideas for reservoir heterogeneity control.