Evaluation on Effect of Alternating Injection Polymer Flooding in Heterogeneous Reservoir

In order to simulate heterogeneous reservoir, six parallel homogeneous cores are used to conduct laboratory experiments of polymer flooding after water drive and the indexes of shunt rate, water cut and recovery factor are compared under different alternating injection cycle of polymer flooding stages. The results show that, when the alternating injection cycle is 0.2PV, it can better restrain profile reversal in the process of polymer injection displacement and make profile reversal appear later. Meanwhile it can improve the sucking fluid proportion of low-permeability layer and make overall water cut stay at low point much longer and then get higher recovery factor. Polymer flooding is a important technology in oil field development, polymer flooding have greatly improve the recovery factor at home and abroad [1,2]. For stronger heterogeneous reservoirs, the pattern of single slug injection can lead to profile reversal easily, resulting in displacement fluid marching forward in low-permeability layer, so there are still a lot of remaining oil in low-permeability layer in no use. Meanwhile, there are many problems in some blocks of some high concentrations of polymer flooding, such as hard polymer injection and large amount of polymer in use [3]. Hence, the optimization of polymer injection pattern, researching the best polymer flooding effect in heterogeneous conditions, is the necessary means of improvement of inhomogeneous oil displacement effect, reduce the amount of polymer injection, and improve the recovery factor of polymer flooding. For the mode of polymer injection, K.P. SONG [4] think that continuously reduce flooding oil viscosity can improve the recovery factor of water flooding of heterogeneous reservoir or after polymer flooding. M. GAO[5] think that the amount of polymer injection in the same conditions, different concentration of polymer slug the more frequently alternating injection the better displacement effect. W.X. WU[6] think that after the larger constant concentrated common polymer slug, go on with polymer flooding pattern of multiple polymer slug in high concentration without variable, molecular weight reduce phase. The thesis used six cores with different permeability, researched the influence of the polymer alternate cycle effects the oil displacement in heterogeneity cases, so as to provide the guidance of the actual production.