Synthesis And Properties Of Size-Adjustable Polyacrylamide Composite Microspheres As Profile Control Agent

Oil exploration in depth has resulted in a lot of wells turning into advanced development with high water, lowering crude oil content in produced fluid. Pore-throat-scale elastic microspheres are deep flooding agent with sizes matched with the rock pores. They not only can block the target pore, change the flow direction of injected water, expand the scope of water flooding, but also can deform elastically under certain pressure and move to deeper strata, obtaining constant plugging and deformation in the whole reservoir and achieving stepwise profile control.In this paper, we synthesize two kinds of organic-inorganic composite microspheres PAMAA@SiO2and SPAMAA@SiO2with core-shell structures potential to be deep profile control agent. The composite microspheres are composed of SiO2as inorganic core and copolymer as organic shell. The swelling capacity, plugging property and rheological property of the composite microspheres are studied. The main contents are as follows:1. The SiO2nanoparticles with diameter of150nm are prepared by sol-gel method and modified with silane coupling agent (KH-570), then the copolymerization is initiated on surface of grafted SiO2by inverse emulsion polymerization. Structure and morphology of the composite microspheres are characterized by scanning electron microscopy, infrared spectrometers, etc. The results indicate that the products are micron composite microspheres with good organic-inorganic core-shell structure.2. Effects of monomer, grafted SiO2, cross linker, initiator and emulsifier are explored on size and morphology of the composite microspheres to determine the optimal synthetic formulation shown below:liquid paraffin/water=30mL/10mL,20drops of emulsifier (Span80),0.1Og grafted SiO2,1.34g AM and0.66g AA as monomers (or adding0.20g of SSS),0.08g cross linker (NMBA),0.02g initiator (APS). The polymerization proceeds under temperature of55℃for4hours.3. Effects of salinity, swelling temperature and swelling time on the swelling capacity of the composite microspheres PAMAA@SiO2and SPAMAA@SiO2have been studied. The results show that the composite microspheres have good stability, temperature and salt resistance, superior swelling capacities. The resistance of microspheres to salinity and temperature is up to300000mg·L-1and90℃, and the products can maintain micron particle size and stable structure even after swelling for14days.4. The plugging property of composite microspheres is preliminarily investigated by simulating stratum pore throat with the nuclear pore membrane. The results show that PAMAA@SiO2and SPAMAA@SiO2can form effective plugging on membrane with aperture of2.7μm. The strongest plugging is formed after swelling3days for PAMAA@SiO2and5days for SPAMAA@SiO2. Then the plugging wanes slowly and the microspheres gradually deform through the membrane.5. Rheological properties of PAMAA@SiO2and SPAMAA@SiO2are studied using stress-controlled rheometer. The results show that the dispersed systems are thixotropic fluid with shear-thinning property. The two systems are pseudo-plastic fluid during the low shear rate range of0-300s-1. PAMAA@SiO2is slightly pseudo-plastic fluid during the middle shear rate range of300-900s-1and is approximate Newtonian fluid during the range of900-1600s-1. SPAMAA@SiO2is approximate Newtonian fluid in the high shear rate range of300-1600s-1. Hysteresis loop exists between the upper and lower equilibrium flow curve, and the systems have reversible rheology as well as good shear resistance.