Study On The Timing Of Polymer Flooding For Ordinary Heavy Oil Reservoirs

The total amount of Bohai heavy oil Reservoir is 34.5 X 10 t,but the initial value of water drive recovery range is only between 18%and 25%with conventional water food technique.For maximum recovery during the short developing period of offshore platform,Polymer flooding was used to improve oil recovery when the water cut reached 60%in bohai oil reservoir,Relatived to the onshore oil field,the offshore experiment of early polymer injection had a success.However,limited by bohai oil reservoir condition and platform lifes,early polymer injection can improve the effect of polymer flooding,the the increase in recovery rate is 5%to 7%.Therefore,when injection polymer can improve the effect of polymer flooding,as the same time as how to confirm the injection timing,is the key to early polymer injection technology for offshore oil field.Therefore,the research on injection timing in heavy oil Reservoir and the evaluation method on injection timing are a priority.First,the critical influences on injection timing of polymer flooding were analyzed.? It showed that the water cut was increased with reservoir heterogeneity,compared with the homogeneous conditions,the polymer injection timing should be earlier;?Injection polymer solution of mobility control ability is weaker,the injection timing is earlier,and then it will have a good mobility control function.The main factors influencing the polymer injection timing is the ability of polymer flooding to improve oil flow rate.Oil-water two phase flow theory indicated that the difference of oil-water mobility ratio in the different water saturation in reservoirs.Therefore,using heterogeneous model carried out the physical simulation experiment research of polymer flooding under the condition of different water transfer.Result concluded that the the optimum injection timing range of polymer flooding was from 0.122 to 0.131PV,which be conformed with the breakthrough time of the water flooding front.According to the theory of water drive front advance,Water injection was about to break,it was the stage of water cut was increasing sharply.And then,Based on the theory of reservoir oil-water relative permeability curve,the stage of water cut was increasing sharply when the water saturation ranges from 0.240 to 0.252.And that was be proved by the result on microscopic oil displacement experiments.When the water was about to break through,the swept volume and oil displacement efficiency were increased maximizely.Therefore,research indicated that when the waterflood front would be breakthrough was the optimal timing of polymer flooding.The waterflood front can be monitored by resistivity method and calculated by water drive front formula.The result were about 0.119PV and 0.123PV injection,near to physical model experiments.So the injection timing can be comfirmed by the real-time detection and calculation of water drive front position...