Study On Physical Simulation Of Polymer Alternate Injection

The field and laboratory experiments showed that the changing of polymer injection could affect the polymer flooding effect, and reasonable injection method could ensure the reduction of amount of polymer under the premise of recovery. In this paper, the optimal injection period of polymer was optimized, and several factors that affected the oil displacement efficiency were investigated, and sweep law was studied.On the base of the physical experiment method, this paper had carried out laboratory physical simulation research on alternating injection of polymer flooding in Daqing oilfield. The results of the study indicate that: for the reservoir with different permeability conditions, enhanced oil recovery value first increased and then decreased with the increase of alternate cycles, and there was an optimum displacement effeciency. The more the permeability ratio was, the more the alternate cycles was when the oil displacement efficiency was the optimum; when the permeability ratio respectively was 2, 4 and 6, the best alternate cycle respectively was 3, 5, 8, recovery percent on the stage of polymer flooding was higher 2.2% than single slug’s; when the permeability ratio was 4, reasonable alternate cycle increased with the decrease of the ratio for effective thickness in low permeability; when the ratio for effective thickness in low permeability respectively was 25%, 35% and 50%, the best alternate cycle respectively was 8, 6, 5, recovery percent on the stage of polymer flooding was higher 3% than single slug’s; fixing the alternate injection mode between high and low concentration of polymer molecular weight could further improve development efficiency, but the oil displacement efficiency was not as good as both the changes in molecular weight and concentration, the difference value of recovery percent of reserves was 4.5%; under the condition of constant pressure, the displacement efficiency for polymer alternate inject was still better than which was for single slug, recovery percent on the stage of polymer flooding was higher 1.6% than single slug’s; comparing with the injection mode of single slug, alternate injection’s pressure conduction was better, there were swept in some degree from the injection end to end of production where the seepage field differences mainly embodied in the low permeability layer, because of the polymer alternate injection, the oil saturation in low permeability decreased significantly and reduced scope was wider, the swept area spread along the main stream line to the two wings obviously; it could be known from the calculation that the overall sweep efficiency of single slug injection mode in high permeability layer was 71.87%, which was 50% in low permeability layer; the sweep efficiency of polymer flooding in high permeability layer increased by 25%, which was 15.62% in the low permeability layer; the overall sweep efficiency of alternating injection mode was 67.19% in the high permeability layer, which was 65.62% in the low permeability layer, the sweep efficiency of polymer flooding in high permeability layer increased by 20.32%, which was 31.29% in the low permeability layer; the overall recovery ratio of alternating injection mode was higher 3.8% than injection mod of single slug’s.