Research On The Polymeric Intelligent Nanosphere Flooding Agents

Intelligent nanogels are widely used in drug delivery and controlled release, cellculture media, biological tissue repair materials, enzyme immobilization etc., becauseof their characteristics of stimuli-responsivity, fast response and good biocompatibility,etc. In addition, intelligent nanogels also show great potential application in tertiaryoil recovery, cosmetics, paint industry and other areas.Polyacrylamide nanospheres are widely used in oilfield as in-depth floodingagent for their excellent properties of water shutoff and deep profile control, due totheir “amoeba” structure. But nanospheres swell so fast that injection pressureincrease, thus limiting their application. In order to control swelling of the polymericnanospheres, this article attempts to combine the stimuli-responsivity of intelligentnanogels and the excellent properties of polyacrylamide nanospheres with watershutoff and deep profile control, a novel intelligent nanogel with controlled swellingproeprties and good sealing strength has been prepared by inverse microemulsionpolymerization and has potential application in in-depth flooding in low-permeabilityoilfield.In this paper, polymeric intelligent nanospheres with temperature-and pH-double sensitivities were firstly synthesized by inverse microemulsion polymerization,and then characterized their structure and morphologies by Fouries transform infraredspectroscope (FTIR) and transmission electron microscope (TEM),respectively.Swelling properties of the polymeric intelligent nanospheres were characterized byzetasizer. Thermo-stability of the polymeric intelligent nanospheres was characterizedby thermogravimetric analysis (TGA). Finally, properties such as water and saltabsorption, gel strength, thermo-resistance, shear-resistance, temperature-andpH-sensitivity of the polymeric intelligent nanospheres were evaluated. Factorsinfluencing these properties such as crosslinker amount, the neutralization degree ofIA, IA and NIPAM mass ratio and initiator amount were investigated. The mainresearch results are as follows:(1) FTIR spectra appeared characteristic absorption peaks of acrylamide unit,itaconic acid unit and N-isopropyl acrylamide unit, which preliminarily confirmed thetarget structure of the polymeric intelligent nanospheres.(2) TGA showed that the polymeric intelligent nanosphere had onsetdecomposition temperature over240℃, indicating its good thermostablity. (3) TEM indicated that the polymeric intelligent nanospheres had spherical-likeand regular shape, with the size range of30nm to75nm and the average particle sizeof47nm.(4) With increasing water swelling time, average particle size of the polymericintelligent nanospheres increased with its boaden particle size distribution. Withswelling time increasing from1h to5h, the average particle size of polymericintelligent nanospheres increased from0.54μm to8.08μm, meeting the requirementsfor ultra-low permeability reservoir EOR with permeability of less than1×10-3μm2and pore throat radius smaller than8μm.(5) In the oscillation frequency range studied, storage modulus G ’, loss modulusG’’ of the polymer intelligent nanospheres changed little with the oscillation frequency,and G’ was significantly greater than G’’. As the stress increased, G ’decreasedgradually while G’’ increased gradually.(6) With the increase of crosslinker amount, water absorption and salt absorptionof the polymeric intelligent nanospheres increased firstly and then decreased gradually,while gel strength, temperature resistance and shear resistance increased gradually.(7) With the increase of IA/NIPAM mass ratio, water absorption and gel strengthof the polymeric intelligent nanospheres increased gradually, salt absorptiondecreased gradually, temperature-sensitive behavior got weakened and pH-sensitivebehavior got strengthened.(8) With the increase of IA neutralization degree, water absorption, saltabsorption and gel strength of the polymeric intelligent nanospheres increased firstlyand then decreased gradually, with these properties reaching maxima at IAneutralization degree of60%.(9) With the increase of initiator amount, water absorption and salt absorption ofthe polymeric intelligent nanospheres increased firstly and then decreased gradually,with these properties reaching maxima at1.2%initiator.(10) Polymeric intelligent nanospheres can swell in different concentrations ofNaCl, MgCl2, CaCl2brine solution, indicating their good resistance to salinityperformance. The rate of absorption of salt order is: NaCl> MgCl2> CaCl2.