Parameter Design Optimization and Practice of Alkaline - Free Compound Flooding in Ordos Low Permeability Reservoir

Jurassic reservoirs in Ordos are typical low permeability reservoirs. After years of waterflooding development, most of them have entered the middle and high water cut stage, and the comprehensive water cut has reached more than 66%, but the recovery degree is less than 30%. Compared with other compound flooding test areas of petrochina, it is difficult to carry out alkali-free compound flooding in Jurassic low permeability reservoirs in Changqing because of low permeability, strong heterogeneity, and higher salinity of formation water and injection water. Therefore, it is necessary to carry out injection experiments of polymer with different molecular weights to establish an injection chart suitable for Changqing oilfield. By using numerical simulation method, the main controlling factors that affect the combined flooding effect are injection/production ratio and polymer adsorption capacity. Field tests show that the effective laws of chemical flooding in low permeability reservoirs are different from those in medium and high permeability reservoirs. The analysis shows that the key factors to enhance oil recovery by chemical flooding in low permeability reservoirs are to keep the chemical injection continuously, to adjust the injection well and to maintain the reasonable formation pressure.