The Experimental Research On Relative Permeability Modifier In Displacement Efficiency

The increase in displacement efficiency of polymer flooding can only be caused by micro forces which do not increase the macro pressure gradient, the elasticity of driving fluid can change the microflow lines in porous media, the increase the micro force which acting on the protruding part of residual oil blob and mobilize the protruding part, so the displacement efficiency of polymer flooding increase.Micro forces have the following characteristics. Viscoelastic fluid can produce more micro forces than the Newtonian fluid, it can largely increase the displacement efficiency of polymer flooding that the micro forces mobilize the small protruding part. Even if the micro forces is smaller the macro pressure gradient, it can move the residual oil blob,the micro forces that are created by the change in flow lines can't impact macro pressure gradient; it can change but macro forces don't change, and it is independent variable in viscoelastic fluid flooding.The parameters characterizing fluid elastic are First normal stress difference, Relaxation time,Deborah number,Storage module, and Weissenberg number, and different parameters have different effects. In the simplified two-dimensional model of the non-equant diameter pore, the degree of change in flow lines for viscoelastic fluid is determined by weissenberg number, weissenberg number is larger and the range of degree is biger, and the piston effect of variable diameter is more significant, and it has larger displacement efficiency of viscoelastic fluid. Then in this research, it is quantitatively characterized the size of the viscoelastic polymer solution that impact on oil displacement efficiency by Weissenberg number. weissenberg number is larger, the viscoelastic polymer solution is bigger, and displacement efficiency increase.By the placement of water-soluble Cr(â…¢)-acetate-HPAM gel in water-wet and oil-wet cores, we research variation of fluid saturation in different size pores, and analyze the oil and water flooding in defferent pores, then recognize the flooding mechanism of water-wet and oil wet cores that is in macroscopic state in different flooding course.During water and oil flooding before gel placement, pores of all size rages in Berea experienced significant gains in water saturation, in contrast in polyethylene, oil was largely immobile in smaller pores; During oil flow after gel placement in Berea, much of the gel was destroyed or experienced a reduction in volume, Swr after gel placement is higher than that before gel placement, oil was traped in Berea in follow-up water flooding, and in polyethylene. extra oil wasn't traped in follow-up water flooding. Injection of gelant mobilized oil in both porous media even though the pressure gradients during gelant placement were less than those during previous floods.In Berea or polyethylene, immediately after gel placement,an extremely high resistance to water flow occurs, presumably because impermeable gel occupies nearly all of the aqueous pore space. During oil fow after gel placement in Berea, much of the gel was destroyed or experienced a reduction in volume, thus leading to a relatively high permeability to oil. In order to select suitable RPM for-on site core, efficiency that is in different polymer concentration, injection volume, injection pressure was contrasted, the result was that the displacement efficiency and cumulative oil production were largest margin of increase while polymer concentration was 1000mg/l, injection volume was 0.4PV, injection pressure was 0.3MPa. On the basis of water flooding, RPM was injected In the above conditions. Displacement effeciency was better in heterogeneous cores than in homogeneous cores. The result of pressure change in RPM flooding and HPAM and Cr concentration in effluent demonstrated that the RPM is illiquid, but if polymer concentration is lower, the RPM fluidity will increase.This research adopted the RPM of different concentration, carried out polymer displacement that was simulated by delayed crosslined gelation in defferent wettability cores after the effluent in water flooding contained more than 98% water and the experiment was stopped. Injecting gelation process was stopped when the effluent contained less than 2% oil, and after the gel formed, follow-up water flooding carried on. The result is below.The efficiency of water flooding in water-wet cores was higher than that in oil-wet cores, the cause was that the oil in the smallest cores wasn't affected in oil-wet cores, in contrast, water entered all size cores and placed the oil out in water-wet cores.In oil-wet cores, because of the different viscoelasticity of RPM in different polymer concentration, with the increase of Weissenberg number, efficiency of polymer placement increased and the lowest water content changed; follow-up gel flooding were affected by the recovery level of early polymer flooding and the recovery inceased then reduced with the increase of of polymer concentration of RPM. Cumulative oil production had the similar trend as recovery.In water-wet cores, polymer recovery trends were same as that in oil-wet cores for different polymer concentration, in contrast, gel recovery were smaller because the gel traped large volume residual oil. Variation trend of cumulative oil production were similar as that of recovery.Due to permeability change before and after gelation injection, and relative permeability curve change, DPR effect of RPM were indicated. The cause was that flow lines were opened during oil injection by gel dehydrating. During follow-up water injection, gel re-hydrated and the open lines closed.