Development Of Branch Polymer For Oil Displacement In Medium And Low Permeability Reservoirs

At present, less than 20 percent of oil can be exploited in low-to-moderate permeability reservoir. It mainly adopts waterflooding in domestic low-to-moderate permeability reservoir, moreover the chemical flooding will be the corollary along with the development of waterflooding later stage. Because of the cost and other reasons, the chemical flooding is most polymer flooding in our country. Through analyzing the characteristics and factors that affect the recovery on the basis of literature investigation, it can be shown that, to ensure the effect of chemical flooding, the oil displacing agent must meet the needs of improving the sweeping efficiency and oil displacing efficiency at the same time.Firstly, based on the performance requirements of polymer flooding for low-to-moderate permeability reservoir, chose 1,3-Diaminopropane and Methyl acrylate as raw material through the molecular design structure, used the reaction of Michael addition and amidation, synthesized and optimized the dendrimers MA2.0 with shear-resistance capacity, and then modified its terminal groups, the dendrimer cytoskeleton monomer DA was obtained. Its structure was confirmed compliance with the design principles after characterized its structure by FTIR and 1HNMR.Then used the dendrimer cytoskeleton monomer DA as core, synthesized the dendrimer polymer HPDA which has smaller molecular radius and better shearing-resistance capacity. Through the orthogonal experimental design method and single factor method, the optimized polymerization conditions were:the dendrimer cytoskeleton monomer dosage was 0.4%; initiator dosage was 0.15%; monomer concentration was 24%; the degree of hydrolysis was 42.8%; functional monomer (AMPS) was 0.5%contents; chain transfer agent sodium formate (CHNaO2) was 10% of the amount of initiator.After the shearing of Warning Stirrer with the speed of 7000r/min for 60s, or borehole shearing of 101mL/min, the polymer solution could still maintain high viscosity retention, generally more than 80%. The HPDA’s molecular weight (Mw) and the radius of gyration (Rg) were analyzed by the Static Light Scattering Instrument (SLS), and the radius of hydrodynamic (Rh) were analyzed by the Dynamic Light Scattering Instrument (DLS), Compared with HPAM, all of the results indicated that HPDA had smaller molecular radius. Through the analysis to the microstructure with the atomic force microscope (AFM) and scanning electronic microscope (SEM) to the HPDA before and after shearing of the polymer, it was found that the HPDA had perfect bending shearing function on its branched structure of the molecular chain that the special construction could still form three-dimensional network structure in solution after shearing.Through displacement experiment, it is found that dendrimer polymer solution of 1000mg/L was qualified with good mobility control performance. In the moderate permeability (100-500)×10-3μm2 formation, the HPDA could establish high resistance factor and residual resistance factor, and could extend the swept volume of polymer flooding furthermore, and could improve the oil recovery of more than 17% in the porous medium.