Study On Characteristics Of Polymer Flooding In Heterogeneous Reservoirs In Bohai

Bohai SZ36-1 oilfield has the characteristics of high oil viscosity,high salinity and heterogeneity.The severe heterogeneity increases the difficulty of polymer flooding in expanding sweep efficiency,resulting in an increase in oil recovery of only about 5%.Therefore,it is necessary to study the law of the efficiency of polymer flooding around Bohai oil reservoir heterogeneity,so as to find an effective method to improve the sweep efficiency of polymer flooding in heterogeneous reservoirs.By using the monitoring technique of resistance?oil saturation to study the oil saturation in polymer flooding and then to analyze the polymer flooding effect and its state of homogeneous and heterogeneous cores.The results show that the heterogeneity of the reservoir will accelerate the breakthrough of the polymer in the large pore,which requires higher polymer mobility control capability.The polymer solution with a single concentration and large slug increase the difficulty of injection,and polymer is prone to profile reversal,which leads to a low sweep efficiency of the polymer solution.In order to improve the injectivity,and inhibit the profile reversal,the alternating injection process of high and low concentration technology was adopted.Finally,the optimization scheme of alternating injection of high and low concentration polymer was selected.Main slag concentration of the polymer solution was 2250mg/L,the slug size was 0.253PV;auxiliary slug concentration is 1500mg/L,the slug size is 0.38PV;the number of alternating high and low concentration 2 times alternative injection of polymer solution.The experimental results show that high concentration polymer alternate injection to a certain extent to ensure the polymer solution injection and prevents the "channeling" phenomenon of the polymer solution in the heterogeneous reservoir,so that the sweep efficiency of polymer solution are improved in the heterogeneous reservoir.But the final recovery(45.17%)is only 0.18%higher than that of the single concentration large slug polymer flooding(44.99%).According to the polymer flood control theory,increasing the residual resistance coefficient can improve the sweep efficiency.Therefore,two kinds of polymers(AP-P4 and HP AM)with different residual resistance coefficients were studied on the basis of alternating injection.The results show that the increase of the residual resistance coefficient of polymer solution in porous media,contribute to the polymer flooding play mobility control effect,increasing the residual resistance coefficient of polymer solution in high permeability layer,and can improve the efficiency of polymer solution in high permeability layers,while forcing the flooding system spread to middle and low permeability layers thus,expand the sweep efficiency of heterogeneous reservoir polymer flooding,and ultimately improve the oil recovery of polymer flooding in heterogeneous reservoir,finally improving the oil recovery of heterogeneous reservoirs.