| Our country has rich resourced of medium and low permeability reservoirs, but due to the limitation of theory and technology, recovery efficiency only 20%, therefore, in the production of low permeability reservoirs has huge potential. Chemical flooding is a key stage in the later period of waterflooding reservoirs. And Polymer flooding is more and one of successful precedent flooding technology in chemical flooding. Partially hydrolyzed polyacrylamide (HPAM) is the most important Polymers in polumer flooding, often used for flow control and permeability. But when use the line HPAM in low permeability reservoirs with low permeability reservoirs of pore in which small, complicated structure, fluid seepage, the strong role of the phase interface make Polymer exist " not inject, not out". For the special requirements of Polymer in the Low permeability reservoirs, this paper from the preparation and modification of functional monomer, redesign of the Polymer molecular structure, and studies its feasibility in and mid-low permeability reservoirs, including the following:1. Base on low permeability reservoirs of low permeability reservoirs, design the molecular structure of Polymer is star structure; make sure in low concentration has a better ability to resist shear and viscous effect.2. Preparation and characterization of modified nano SiO2 functional monomer, mainly including use the silane coupling agent modification the hydroxyl on the surface of nano-SiO2 and react with maleic anhydride to increasing the activity of modified monomer. Optimize the optimum reaction conditions for monomer:toluene as the solvent, reaction temperature is 80 ℃, reaction time is 12 hours. Characterization of the monomers by Thermogravimetric analysis (TGA), Infrared spectrum (IR) and Nuclear magnetic resonance (’HNMR).3. The preparation of Polymer Modified nano-SiO2/AA/AM, using the orthogonal-single factor-orthogonal method to determine the optimal synthetic conditions:total monomer concentration is 26%, AM:AA= 8.2:1.8, amount of initiator is 0.2%, reaction temperature is 40℃, pH= 7.4, modified nano SiO2 functional monomers quantity of 0.3% of the total monomers. And characterization the Polymer by Infrared spectrum (IR) and Nuclear magnetic resonance(’HNMR); determine the molecular weight of Polymer is about 11 million to 13 million and hydrodynamic radius is 150 nm to 200 nm, at the same time confirme the three-dimensional network structure of Polymer by scanning electron microscopy (SEM).4. The evaluation of Polymer Modified nano-SiO2/AA/AM, Polymer has good increase viscosity ability and heat resistance:the 1000mg/L Polymer solution’s viscosity is about 300mPa-s at 65℃ and the Polymer solution’s viscosity rentention rate is above 74.0% when the temperature from 20℃ to 90℃. Polymer has good shear resistance and rheological properties: Wu Yin shear and perforation shear experiments show that under 65℃,1000 mg/L Polymer solution at high shear rate (11500 r/min,80.8 ml/min), the viscosity retention rate is above 77.9%.Study on the injection, the resistance factor (RF) and residual resistance factor (RFF) of Polymer in the low permeability reservoirs (50～500×10-3μm2); the results show that the 1000 mg/L Polymer-20 in the middle permeability reservoir (K=300×10-3μm2), the injection pressure is less than 0.6MPa; In low permeability reservoir (K=100×10-3μm2), the injection pressure is less than 3.0MPa; so the Polymer has good injection performance in low permeability reservoirs. Polymer-20 can increase water phase viscosity and greatly reduce the permeability of water phase in porous media to reduce the mobility ratio, greatly improve the sweep efficiency of Polymer in low permeability reservoirs, and have the effect of mobility control. The permeability scope of application for the Polymer modified nano SiO2/AA/AM is from 100×10-3μm2 to 500×10-3μm2.Experiments show that the Polymer modified nano-SiO2/AA/AM has good shear resistance, good heat-resistant and rheological properties. At the same time the Polymer have better performance of injection and mobility control ability, so has good feasibility in low permeability reservoirs.
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