Research on the properties of in situ emulsified active associative polymer with low molecular weight based on low permeability oil reservoirs

The development of oil and gas resources in low-permeability reservoirs is being paid more and more attention. Moreover, oil and gas resources in low-permeability reservoirs are affluent, and the water cut of the medium permeability layer is so high that the injection capacity has decreased significantly. Therefore, it is of great importance to address the issues of injectability and enhance oil recovery in low-permeability reservoirs. Given the existing conditions of low permeability and high water cut in Daqing Oilfield, the synthesis of an in situ emulsified associative polymer (ISEPAM) is the focus of the research. The polymer was prepared by micellar polymerization, ensuring a molecular weight of 5 × 10⁶ Dalton. A series of experiments were conducted to investigate its dissolution filtration property, viscosifying, emulsification, anti-adsorption, conductivity, and oil displacement capacity. The experimental results show that ISEPAM has more significant properties than the polymeric surfactant (HB) used in Daqing Oilfield. The ISEPAM solution has significant filterability (filter factor is 1.1), viscosifying (38.66 mPa·s), emulsification (the water evolution rate of ISEPAM was only 4.4% for 60 min at 90% water cut), and good anti-adsorption property (after five adsorptions, still has a viscosity retention rate of 65%) in a specific concentration (1000 mg/L) and the field water in Daqing Oilfield (salinity is 4996.3 mg/L). The reason for this is due to the presence of dynamic reversible networks in the ISEPAM solution, and there are no cationic functional groups on the polymer chain. The conductivity of ISEPAM was tested using a homogeneous square core with 48.1 mD permeability, and the results show that the viscosity retention rate of the effluent can reach 90% and excellent injection property can be achieved. In the oil displacement test, ISEPAM presents excellent sweep efficiency and enhanced oil recovery by about 25% under 50 mD permeability. Under low permeability conditions, the ISEPAM exhibits better injectability and excellent oil displacement capacity. The related findings can provide an important idea and reference for the design and development of EOR polymers in the reservoirs with low permeability or high water cut.