The Preparation Of Vermiculite Modified Polyacrylamide Core-shell Emulsion And Its Application Evaluation In Enhancing Oil Recovery

With the exploitation of oilfield, reservoir characteristics and constantly changing environment, especially during the high water-cut stage, which the fluid advantage channel developed, Invalid injected water circulation, reservoir sweep efficiency is low. These factors lead to some problems such as the low oil recovery, waterflooded, equipment corrosion and sewage treatment costs too much in the late. Therefore the polyacrylamide crosslinked microsphere often used as a new deep profile control and water shutoff technology to enhance oil recovery in oil field. Vermiculite is a kind of natural silicate minerals, it has excellent properties of expansion and water absorption. The size of the composite microspheres increased significantly when vermiculite was added in the synthesis process of the polyacrylamide nanometer microspheres. The inorganic vermiculite as the core ensures the complex microspheres particle size, while the hydrophilic polyacrylate on the surface of the core enhances the hydrophilicity of microspheres. Nano composite microspheres have small particle size so that they can be easily injected into the deep formation to achieve deep profile control. Due to higher swelling of these microspheres, their volume increased rapidly and the advantage channels of flow were blocked after injecting these dilatants into the formation. So it’s of great significance for the effect of stabilizing oil production by water is achieved in maturing reservoir and the effect of water-injection development waterflooding is improved in offshore oilfields and low permeability reservoir.Using white oil as the continuous phase, a blend of surfactants(Span80/OP10/oleic acid) as emulsifying system and 42.86% aqueous solution of acrylamide as the dispersed phase, the inverse microemulsion was prepared, including 47.1% white oil, 13.7%Span80/OP10/oleic acid(7.0:3.0:2.0) emulsifiers and 39.2%aqueous solution of acrylamide. The inorganic vermiculite was added in the polymerization system during the preparation of polyacrylamide inverse emulsion and the composite polyacrylamide microspheres(composite PAMCMS) with core-shell structure were obtained. Using the emulsion stability, monomer conversion rate, gel formation rate, particle diameter, swelling property and as indicators, the effects of oil-water ratio, monomer AM, initiator, monomer AA, neutralization degree, vermiculite, crosslinking agent, stirring rate and reaction time on the polymerization were investigated.We found that when the proportion of initiator APS-SHS(molar mass ratio is 1:1), crosslinking agent MBA, monomer AA(the neutralization degree was 88.6%) and vermiculite in monomer AM was 0.9%, 0.25%, 23.4% and 2.5%, respectively, the latex particles with particle diameter of 748.9nm could be obtained under stirring rate 350 r/min at the temperature of 40℃. The reactor time was lasting 9 hours. The novel microsphere was swelling at 70℃ for 15 days in pure water and mineralized water, respectively. The swelling ratio of composite PAMCMS was up to 5.37 times in the pure water, it also shown its higher salt tolerance in the mineralized water and the size was up to 3291.2nm, increased by nearly 4.4 times after volume expansion; The composite PAMCMS solution(liquid concentration was 3000mg/L) can realize fast dispersion under 1000 rpm stirring rate in 15 min, its good water solubility and dispersion of injection ensured that it can uniformly enter into the deep formation when reached bottom of reservoir, not caused the closure in the zone near wellbore due to the presence of large particles that were not dispersed. The combination of the composite PAMCMS emulsion, betaine and SAS-60 showed a good synergistic effect which the interfacial tension of Changqing oil and mineralized water can be reduced to 10- 4m N/m.In addition, the expanded composite PAMCMS can block effectively the pore of simulate sand pack tube. After expanded composite PAMCMS were injected in the tube, the total recovery rate increased significantly from 65% to 81.8%. The result of composite PAMCMS injection process optimization found that low injection concentration and longer injection time of injected polymer nanospheres can effectively expand the water swept and volume, increase greatly the oil recovery.