Experimental investigation on associative polymers to greatly enhance oil recovery in heterogeneous reservoirs

Compared with partially hydrolyzed polyacylamide (HPAM) and glycerinum, the unique characteristics of associative polymers (AP-H1 and AP-H2) to generate the flow resistance, control the adverse mobility, especially regulate the macro-/micro- heterogeniety were systematically studied through different laboratory measurements in one-dimensional sand-packed models and two-dimensional visual models. And the feasibility to greatly enhance oil recovery by associative polymer combination was verified based on the special characteristics. The results show that, AP-H1 and AP-H2 not only could keep a relatively good injectivity and penetration behavior at a lower permeability of 314 × 10−3 μm2, but also could establish the resistance factors that were orders of magnitude higher than HPAM (2000 mg/L) at similar even lower apparent viscosity or lower concentration. At similar viscosity, the oil (2122 mPa·s) displacement by AP-H1 (1200 mg/L) could achieve a better mobility control effect and obtain greater oil recovery than that of HPAM to displace the oil of 303.6 mPa·s. Under different macro-/micro- planar and longitudinal heterogeneous conditions of a permeability contrast of 2–10 times, when displacing oil of different viscosity (15–2122 mPa·s), AP-H1 could achieve significant mobilization and greater sweep to low permeability zones and obtain a greater EOR value, even could lead to the fluid diversion of the post-water injection to a certain extent. In addition, AP-H1 could further obviously activate the most of the cluster-like residual oil in both outer large and inner small channels over the glycerol and HPAM, namely present a good ability to regulate the micro-heterogeneity. More importantly, at the permeability contrast of 10 times, the slug combination of associative polymers (AP-H2 + AP-H1) not only could ensure greater sweep to the high-permeability layer, but also could achieve the maximum impact on the low-permeability layer, which obtained significantly higher oil recovery than single polymer slug or "associative polymer + HPAM" combination slug. Finally, it can be indicated that associative polymers have great feasibility to significantly enhance oil recovery in heterogeneous reservoirs based on the reasonable design of molecular structure and slug combination of associative polymers. The findings of this study can help for better understanding of the mechanism of mobility control and heterogeneity regulation of associative polymer, as well as the oil displacement effect by slug combination of different associative polymers, and also can provide a new design idea for the efficient development of heterogeneous reservoirs.