| The second type B reservoirs of Daqing L Oilfield has been shifted from water flooding to polymer flooding.However,due to poor rock properties and significant heterogeneity of the reservoirs,the overall effect of polymer injection has been unsatisfactory and the results vary greatly between different areas.The complex distribution of remaining oil indicates that the current injection parameters of the polymer do not match the reservoirs well.Therefore,it is necessary to conduct an optimization study of the injection parameters for polymer flooding based on the physical properties of the different types of reservoirs in the second type B reservoirs of L Oilfield.This article analyzes the changes in viscosity of the polymer solution under different influencing factors,such as its thickening properties,shear resistance,and tolerance for high temperature.It has determined the relationship between different molecular weights and concentration of the polymer and permeability of the second type B reservoirs in different areas.The injection parameters for polymer flooding were optimized for the heterogeneous conditions both within and between layers in the second type B reservoirs of the L Oilfield in Daqing,leading to the following insights:（1）The high molecular weight and high concentration polymer solution used for the second type B oil layers in Daqing L Oilfield has a higher viscosity but lower shear resistance and temperature resistance.Therefore,when optimizing the polymer injection parameters,if the oil recovery rates are similar for different injection schemes,it should be avoided to use high molecular weight and high concentration polymer.（2）For the reservoirs with permeability of 200×10-3μm2,400×10-3μm2,and 600×10-3μm2 in the second type B oil layer,the molecular weight and concentration of the suitable polymer were determined.The optimal injection parameters for the homogeneous reservoirs with a permeability of 200×10-3μm2 are a molecular weight of 1200×104 and a concentration of 1200mg/L.Compared to water flooding,the oil recovery rate can be increased by 21.3%with this scheme.For the homogeneous reservoirs with a permeability of 400×10-3μm2,the optimal injection parameters for the polymer are a molecular weight of 1900×104and a concentration of 1200mg/L.Compared to water flooding,the oil recovery rate can be increased by 21.6%with this scheme.For the homogeneous reservoirs with a permeability of 600×10-3μm2,the optimal injection parameters for the polymer are a molecular weight of 2500×104 and a concentration of 2500mg/L.Compared to water flooding,the oil recovery rate can be increased by 28.9%with this scheme.（3）Through a three-tube parallel rock core displacement experiment,the injection parameters of polymer flooding for the heterogeneous reservoirs in the interlayers of the second type B oil layer in Daqing L Oilfield have been optimized:the injection molecular weight is 1900×104,the injection volume is 0.5 PV,and the injection method is gradient viscosity reduction.Compared with water flooding,the oil recovery rate under this scheme can be increased by 18.10%,and the cumulative oil recovery rate is 50.16%.（4）Through a long and narrow heterogeneous core displacement experiment,the injection parameters for polymer flooding in the non-homogeneous reservoirs of second type B oil layer in Daqing L Oilfield were optimized:the injection molecular weight is 1900×104,the injection volume is 0.7 PV,and the injection method is gradient viscosity reduction.Compared to water flooding,the oil recovery rate can be increased by 16.77%with this plan,and the cumulative oil recovery rate is 48.83%.Through the above experimental research and evaluation,a complete injection and flooding plan design has been made for the second type B oil layer in the L oilfield,providing theoretical basis for developing the adjustment strategy of polymer drive tracking in the second type B oil layer. |
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