Synthesis And Performance Of Polymeric Nanospheres Flooding Agent With High Strength And High Temperature-Resistance

Currently, most of our oil fields have entered the late mining with high water and increasing reservoir heterogeneity. The ultimate oil recovery depends on sweep efficiency and oil displacement efficiency. Long-term water flooding exacerbated the reservoir heterogeneity, forming large pores in the reservoir, resulting in water flooding "short circuit." Therefore, in order to realize stable oil production, and improve oil economic development benefits, some methods, such as heterogeneity improvement of the inter-layer, expanding water sweeping volume, changing the flow ratio of the flooding and the displacing fluid by way of deep flooding techology, have become important means to improve flooding effect.In this paper, the polymeric nanosphere flooding agent with organic and inorganic double network structure as well as high strength and high temperature-resistance, was prepared by inverse microemulsion polymerization. Performance of the microemulsions was discussed. Factors influencing the water absorbency, salt absorbency, gel strength, shear-resistance, pH-sensitivity, thermo-resistance and expansibility of the polymeric nanosphere flooding agent, such as the crosslinker amount, hectorite amount, the mass ratio of itaconic acid to acrylamide and itaconic acid neutralization, etc, were investigated. Morphologies, structure and heat-resistance of the polymeric nanosphere flooding agent were characterized by TEM, X-ray diffraction, FTIR and TGA, respectively. Polymeric nanosphere flooding agents with particle size of30-65nm, gel strength of13.56Pa.s, temperature-resistance of120℃and good water absorbency and salt absorbency, were obtained. Particle size of the polymeric nanosphere flooding agents increased to3-5μm after300min water absorbing, meeting the ultra-low permeability reservoir EOR requirements of permeability less than1×10-3μm2and pore throat radius less than8μm. The main research results are as follows:1. Polymeric nanosphere microemulsion had good mechanical stability, dilution stability, temperature-resistance and frost-resistance.2. With increasing of the crosslinker amount, water absorbency, salt absorbency, pH responsitivity and expansibility of the polymeric nanosphere flooding agents decreased, while gel strength, temperature-resistance and shear-resistance increased. When the chemical crosslinker amount was0.2-0.4%, the equilibrium water absorbency reached83-125g/g. The polymeric nanosphere flooding agent had gel strength as high as13.56Pa. s and temperature-resistance as high as120℃when the chemical crosslinker amount was0.6%. Particle size of the polymeric nanosphere flooding agents increased to3-5μm after300min water absorbing, meeting the ultra-low permeability reservoir EOR requirements of permeability less than1×10-3μm2and pore throat radius less than8μm.3. With the increase of itaconic acid/acrylamide mass ratio, water absorbency and salt absorbency and pH-responsivity of the polymer nanosphere flooding agent increased firstly and then decreased. Water absorbency and pH-responsivity of the polymer nanosphere flooding agent reached the maxima at itaconic acid/acrylamide mass ratio of15:85.While salt absorbency of the polymer nanosphere flooding agent reached the maxima at itaconic acid/acrylamide mass radio of20:80.4. With increasing of the hectorite amount, water absorbency, salt absorbency, pH responsitivity and expansibility of the polymeric nanosphere flooding agents decreased, while gel strength, temperature-resistance and shear-resistance increased. When the hectorite amount was1%, the polymeric nanosphere flooding agent had gel strength as high as9.1Pa.s and temperature-resistance as high as120℃. Particle size of the polymeric nanosphere flooding agents increased to3-5μm after300min water absorbing, meeting the ultra-low permeability reservoir EOR requirements of permeability less than1×10-3μm2and pore throat radius less than8μm.5. With the increase of itaconic acid neutralization, water absorbency and salt absorbency of the polymer nanosphere flooding agent increased firstly and then decreased. Water absorbency and salt absorbency of the polymer nanosphere flooding agent reached the maxima at65%itaconic acid neutralization.6. Polymeric nanosphere flooding agent can swell in different concentrations of NaCl, MgCl2, CaCl2brine solution, indicating their good resistance to salinity performance. The rate of absorption of salt order is:NaCl> MgCl2> CaCl2.7. In the oscillation frequency range studied, storage modulus G’, loss modulus G" of the polymer nanosphere flooding agent changed little with the oscillation frequency, and G’was significantly greater than G". As the stress increased, G ’decreased gradually while G" increased gradually.8. FTIR spectra appeared characteristic absorption peaks of acrylamide unit, itaconic acid unit and hectorite unit, which preliminarily confirmed the target structure of the polymer nanosphere flooding agent.9. XRD showed that the polymer nanosphere flooding agent did not show hectorite sharp diffraction peaks while a wide dispersion peak appeared in a wide range, indicating that the crystal structure of hectorite had transformed into amorphous structure, with hectorite randomly distributed in the polymer matrix.10. TEM indicated that the polymer nanosphere flooding agent had spherical-like and regular shape, with the size range of30nm to65nm and the average particle size of43nm.11. TGA showed that the polymer nanosphere flooding agent had onset decomposition temperature over252℃, indicating its good thermostablity.