Preparation And Oil Displacement Mechanism Of Nano-scale Polyacrylamide Microspheres

Now,enhanced oil recovery by nano-fluid technology is an important development direction of oilfield exploitation.As one of the emerging profile control and flooding agents,polyacrylamide microspheres have good salt resistance,high temperature resistance,and deformability.They can enter the deep part of the reservoir with the water phase for profile control and flooding.Then they can improve oil recovery by improving the swept volume and oil washing efficiency.At present,most of the microspheres are of the micron level,which cannot smoothly enter low-permeability reservoirs,which are widely distributed in our country.In response to this situation,in this paper,reverse microemulsion polymerization was used to prepare three kinds of nano-sized polymer microspheres,and the oil displacement mechanism of nano-scale polymer microspheres were analyzed through rheological experiments,microchannel experiments,and oil droplet stripping experiments.Firstly,we controlled the polyacrylamide particle size by adjusting the amount of composite emulsifier and stirring speed.Three nano-scale polymer microspheres with average particle sizes of 54,93 and 295 nm were synthesized,and the swelling ratio was controlled at 2 to 3 times.The microspheres have good heat resistance and salinity resistance,begin to decompose at 320 °C,and can be used in deep reservoirs.The dispersion properties of nano-scale polymer microsphere emulsions are affected by factors such as particle size,membrane pore size,stirring time,and number of membrane layers.In the flooding experiment of sand-packed pipes,sample 2 with a particle size of 93 nm has the best effect on low-permeability sand-packed pipes,and can achieve an enhanced oil recovery efficiency of 27.86 %.Sample 1 with a particle size of 54 nm has the best effect on high-permeability sand-packed pipes.Secondly,through rheological experiments and micro-channel experiments,the oil displacement mechanism of nano-scale polymer microsphere emulsions is explored:the shear viscosity of nano-scale polymer microspheres changes significantly with the change of shear rate,and is affected by temperature,mineralization,the degree of chemical conversion and concentration.This change can adjust the amount of water entering the oil layer with different permeability;at the same time,nano-scale polymer microspheres can change the wettability of the channel surface through deposition and water film spreading,thereby improving the oil displacement efficiency.The change of microchannel surface wettability is related to the synergistic effect of nanoparticles and surfactants.In the oil droplet stripping experiment,nano-sized polymer microspheres with a particle size of about 54 nm and surfactants have a synergistic effect,thereby accelerating the process of stripping crude oil droplets from the solid surface.The above oil displacement mechanism has significant guiding significance for the use and improvement of nano-scale polymer microsphere oil displacement agents.