The Preparation Of Cationic Microspheres And Its Mechanisms Of Interfacial Interaction With Polymer

As most oilfields in East China have been in the late stage of water injection, the further development of these oilfields is severely impeding by vain cycles of water injection and thus increasingly heavy burden of water treatment on surface. One solution is the in-depth profile modification. The polymer microspheres with tunable size and controllable swellability, are appropriate for this solution choice. Microspheres for profile modification are functioning to plug water channel by viscosification, adsorption and retention after being swollen. To improve its performance, the incorporation of cationic monomer when synthesizing microspheres is of great significance for two reasons: firstly it increases the water adsorbing power, which accordingly enhances viscosity and retention; secondly, it is apt to be attracted on the negative-charged pore wall with surface by electrostatic attraction which improves adsorbance and also retention.Referring to works reported before, the cationic microspheres with varied scales were synthesized by inverse microemulsion polymerization, inverse concentrated emulsion polymerization and inverse suspension polymerization with acrylamide and methylacryloxylethyl trimethyl ammonium chloride as monomers. Based on the property analysis, the relationship of viscosity to nanosphere concentration, the compatibility between microspheres and pores, the flocculation between partial hydrolyzed polyacrylamide(HPAM) and microsphere are probed. Specifically, this dissertation was further categorized into the following five parts.1. Nanospheres with cationic degree 0~50% and diameter less than 100 nm were synthesized by inverse microemulsion polymerization. Their composition and structure were characterized by infrared spectrometer and transmission electron microscope. The multi-step addition method is used to well solve the problem of high content ratio of surfactant to monomer in microemulsion, and finally the microemulsion with 35~40% solid content is obtained. The step number is optimized to three times by solubilization limits after each step according to size change by dynamic light scattering technique. By this new method, the translucent products were synthesized, which is different from the milky-state product synthesized by semi-continuous feed method. This new method also avoids the size-fluctuating problem in continuous feed method.2. The submicron microspheres with cationic degree 0~20% and 0.4~5 μm were synthesized by concentrated emulsion polymerization. The conductivity is easily used to detect formation and destability of concentration emulsion. Due to viscous shear breakup, the bimodal size distribution of drop size evolving to unimodal of particles is testified by microscope observation and viscosity measurement. The produced emulsion has been stable for 6 months, which illustrates that concentrated emulsion polymerization is a good solution for the instable problem of conventional latex emulsion.3. According to the feature that particle size is tricky to control due to a number of factors, the size distribution rule in inverse suspension polymerization was statistically analyzed based on the turbulence emulsification theory in liquid-liquid dispersion. The results show that the microspheres with 10~500 μm are synthesized under varied factors. In these factors, the mean particle size decreases with the increasing dispersant concentration, stirring speed, monomer concentration in water phase, crosslinker concentration and drop size, and increases with increasing water phase volume fraction, initiator concentration and interfacial tension; the cationic monomer content in total monomer has a little effect on particle size. On the basis, the inverse microemulsion of microspheres is used as dispersant to regulate the breakup of droplets, by which the particle size distribution index is decreased and particle shape is changable.4. The microsphere concentration in some applications has been increased beyond the applicable scope of available equation with the formation deteriorating. Within a larger range of nanoparticle concentration 0.1~1wt%, the viscosity evolution of varied cationic degrees perfectly corresponds to the Krieger-Dougherty model modified by Tan et al., which largely extends microsphere concentration depicted by available model. In this model, the specific volume and its decreasing index uncover the interaction extent of particles, including intertangling effect and osmotic deswelling by counterion. Moreover, the viscosity index in Herschel-Bulkely equation reflects the microsphere concentration at maximum extent of electroviscous effect. Additionally, the compatibility between varied scale microspheres and formation permeability was valued by sand tube test. The results show that the noionic nanoparticles was applicable for permeability lower than 800 ×10-3μm2, where nanoparticles with 10% cationic degree increased the permeability range to 1200 × 10-3 μm2; the submicron particles synthesized by concentrated emulsion polymerization were well applicable for a medium-high permeable formation.5. The flocculation behaviors of cationic microspheres and HPAM were quantitively explored by analysis of particle size, turbidity, viscosity and precipitation volume. The results show that, the combined system with nanoparticles and HPAM evolves from aggregation to relatively uniform dispersion at a critical salt concentration(CSC); while the combined system with microparticles and HPAM evolves from bulk to single-particle dispersion. The CSC is closely related to the cationic degree of particles. The structure evolution of these flocculations systems is reversible. The plugging efficiency can be largely improved by flocculation formation that subsequent HPAM is injected after microsphere injection when the mismatching problem between microspheres and pore throats occurs. And this flocculation plugging is removable by water with higher salinity than CSC. The flocculation feature explored here has great potential for the residual HPAM reutilization after polymer flooding and the profile modification by combined system.