Experiment Study On Chemical Flooding Enhanced Oil Recovery In Bohai LD4-2Oil Fields

LD4-2Oilfield has the complosite fault block structure, which with big reservoir thickness, high average permeability, serious heterogeneity, low viscosity of crude oil, high salinity of formation water and other characteristics. According to the prediction of the numerical simulation, when the moisture content get85%to95%, oil recovery of LD4-2Oilfield is only20.1%to33.4%,it needs to be carried out the recovery measures with further improvement. Currently the polymer (general partially hydrolyzed polyacrylamide) in use is difficult to adapt to the next step in development requirements of LD4-2Oilfield, as the salt resistance, shear resistance and stability of the ploymer is poor. In connection with the development requirements of LD4-2Oilfield,.according to theory of reservoir engineering and physical chemistry, the author uses instrumental analysis and physical simulation as technical means to carry out the screening of the displacing agent and its performance evaluation, and conducts the study of the its flow characteristics the oil displacement efficiency and experimental f oil displacement efficiency on this basis. The results show that, the displacing agent which use the configuration of the demineralized water has higher viscosity, better stability, better anti-shear capacity, bigger molecular coil dimension Dh, stronger expanding capability of the swept volume, the increase of recovery rate is higher, as compared with water displacing agent which use the configuration of the source water. The interfacial tension between P/S systems which uses surface active agent "SUN4" and crude oil can reach10-3mN/m magnitude. Compared with the " Kangyan " polymer solution and the P/S systems, the capacity of expanding swept volume of Cr3+polymer gel is stronger, the increase of recovery rate is higher. The influence of the expanding swept volume effect of oil displacement agent on the recovery factor is more obvious than the influence of oil displacement effect. It is recommended that LD4-2Oilfield used "Gaofen" Cr3+polymer gel (or a modified P/S systems) in chemical flooding,"Gaofen" polymer, China Petroleum Daqing Refining&Chemical Company produced partially hydrolyzed polyacrylamide (relative molecular mass is1900×104, solid content is88%), the concentration range is CP=1000mg/L～1400mg/L, slug size range is0.19PV～0.38PV, the increase of expected recovery is6%to8%. The "sodium hydroxide-sodium carbonate" is recommended to the softening treatment of source water.