Study On Optimization Of Staged Reasonable Injection Rate Of Polymer Flooding

For the inefficient cycling problem of polymer flooding,the influence of injection rate on the seepage law of polymer solution in porous media is fully considered on the basis of polymer step-down viscosity injection in this paper,then physical simulation and numerical simulation are used to carry out experimental verification and optimization for the injection rate of well groups.At first,carry on the core flow measurement experiments at different injection rates and calculate the inversion of oil-poly relative permeability curves using flooding experimental data.The results show: Different polymer systems show different curve morphologies at different injection rates,high concentration slug has the largest span in its two-phase interval at low injection speed.And the permeability curve of the polymer solution phase becomes lower and lower at the same water saturation with the increase of injection rates.But in the experiments with medium concentration and low concentration slugs.The intermediate injection rate has a two-phase interval span which is higher than other rates.In resistance factor experiment,the resistance factor becomes smaller with the increase of the injection speed,that is,the polymer is not likely to cause flow difficulties around the injection well due to the high-speed flow.Secondly,through the physical simulation experiment of three-dimensional inter-layer parallel plate model to study the control direction of the reasonable injection speed in different stages of polymer flooding.The results show: In water cut declining-stage,increasing the injection rate will contribute to a high saturation oil wall at the front of the displacement which can make a good control about the mobility.In low water cut stage,increasing speed under limit pressure can help maintain high injection pressure in order to displace the oil wall effectively.In water cut rising-stage,increasing injection rate under limit pressure can make the middle and low permeability layers with sufficient pressure gradients,then obviously increase the sweep volume of the middle and low permeability layers.At last,basing on the historical matching of lab physical simulation experiments,combined with the actual well group model in the oil-field,the numerical simulation method was used to optimize the injection rate at different stages.The results show that increasing injection rate can help to maximize ultimate recovery.In addition,during the water cut rising-stage,in the case of a single well with a controllable amount of injection,the injection volume of each injection well in the well group should be optimized to obtain the maximum recovery.