Study On Reasonable Polymer Injection Parameters For The Development Mode Of “Combination Of Second-class Reservoir & Tertiary Recovery”

Polymer flooding is able to enhace oil recovery by increasing displacing fluid viscosity, reducing mobility ratio of displacing-displaced fluid and enlarging swept volume. In order to solve the problem that the producing degree of low permeability layers is low, the amount of remaining oil within thick layers is is still enormous and the vertical producing degree is asymmetrical after polymer flooding due to the serious anisotropism of second-class reservoir layers, Labeibei Second Block started “Second&Tertiary” experience in 2006: on the basis of infilled well pattern of tertiary recovery, the thick layers are perforated selectively and then explored by water flooding; the left layers are perforated after the experience and ultimately explored by polymer flooding. However, due to injection-production imbalance and low viscosity of the injection system, the block injection pressure increased slowly, swept volume of polymer was small and monolayer breackthrough happened in some wells, as a result of which, the concentration of produced fluid increased quickly and the decreasing amount of water cut was small. This thesis conducted core displacement experiences and numerical simulation to study the influence of different polymer parameters on the development effect, determine reasonable injection rate and polymer parameters and compare the development effect of polymer flooding with or whitout “Two&Three”. The results are as follows:By conducting displacement experiences with parallel cores, the changing characteristics of shunt rate in each core layer with and without “Two&Three” were compared. The result shows that the recovery effect reaches the best by adopting the polymer with molecular weight of 25 million and slut of the echelon decrease concentration. The development effect of polymer injection scheme with “Two&Tree” is better than that without “Two&Three” and the ultimate recovery is enhanced by 1.28%. By conducting displacement experiences with cores of three layers heterogeneity, the formation pressure, oil recovery rate and the degree of EOR were researched in the conditions of different stages, injection rate and layers with different permeability. The result shows that development effect of the scheme with 0.16-0.2-0.18PV/a reaches the best, the oil recovery reaching to 64.10%.Through numerical simulation, the reasonable polymer injection parameters, slut combination and injection rate is optimized, ultimately the optimal scheme was determined: 0.2 PV of protection slut(molecular weight of 25 million and concentration of 1400 mg/L), injection rate of 0.16PV/a + 0.3 PV polymer flooding slut(molecular weight of 25 million and concentration of 1200mg/L), injection rate of 0.20 PV/a +0.5 PV decrease concentration slut(molecular weight of 25 million and concentration of 1200mg/L). Finaly the development effect of adjusted scheme is predicted and the ultimate recovery reaches to 57.58%.