Preparation And Evaluation Of Polyacrylamide Microspheres For Enhanced Oil Recovery

Limited by low polymer content and high cost of emulsifiers employed, polyacrylamide microspheres can't be widely applied in Enhanced Oil Recovery. To address these problems, twice polymerization process and new emulsifiers with potential ultra-low IFT were studied.Assisted by electrical conductivity meter, W/O microemulsions were prepared with diesel oil, acrylamide solution and emulsifiers. Then, with the constituents of microemulsions defined by pseudo-ternary phase diagram, two kinds of polyacrylamide microspheres with different emulsifiers were successfully synthesized. In microemulsions stabilized by Span80/Tween80 with the mass ratio of 3/1, mass fraction of diesel oil, emulsifiers and acrylamide solution separately accounts for 43.0wt%, 17.4wt% and 39.6wt%; for microemulsions made by LA/Span20/Tween60 with the mass ratio of 5/3/2, diesel oil, emulsifiers and acrylamide solution respectively occupies 46.0wt%, 16.0wt% and 38.0wt%. Temperatures are both set at 30.0℃, stirring speed ranges from 400 to 700rpm, acrylamide concentration of the solution is 62.0wt%. Usage of APS accounts for 0.098wt% of the acrylamide, and that of SHS is 0.041wt%, while crosslinker MBA can be adjusted for the water absorptivity of nanospheres. Polymer content of the microspheres products can be lifted by over 10wt% via twice polymerization process; meanwhile, the amount of emulsifiers can be reduced by about 5wt%.Transmission electron microscope, laser particle scanning analyzer and rheometer were adopted for qualitative and quantitative evaluations. Original diameters of the microspheres are less than 100nm; however, after water absorption they can reach several hundred microns, their aqueous solutions belong to dilatant fluids. Dynamic IFT measurements by spinning drop interfacial tension meter show that Span80/Tween80 has good synergic effects separately with alkali and surfactants in achieving ultra-low IFT values (<10-2mN/m) between Zhuangxi heavy oil and formation water; while LA/Span20/Tween60 merely neutralized by alkali exhibits satisfying performance in decreasing IFT to ultra-low values. Moreover, sandpack tests indicate that injection of microspheres and succeeding water flooding can contribute more than 20% OOIP to the primary recovery of Zhuangxi heavy oil; microscopic oil displacement demonstrate that: LA/Span20/Tween60 neutralized solution possesses better performance in improving displacement efficiency than Span80/Tween80 solution with the same concentration.It can be concluded that the twice polymerization process can significantly improve the polyacrylamide content of the microspheres products. Besides, oil displacement efficiency can be increased by emulsifiers with ultra-low IFT properties; therefore, enlargement of sweep efficiency and improvement of displacement efficiency can be simultaneously acquired. Experimental studies in this paper are of tremendous value for future large-scale application of nanospheres in EOR.