Preparation And Properties Of Nano Microspheres And Cellulose Composite Gels For Well-killing Application

During underbalanced well killing,gel valve has been widely used because of its low operating cost and pollution-free to oil and gas.However,for high pressure stratum,the composite gel is weak in mechanical strength and easy to crush under high pressure,so it can not achieve the sealing effect.To overcome this shortcoming,in this paper,acrylamide / hydroxyethyl methacrylate(AM/HEMA)copolymerized microspheres;polymerizable nano microspheres with double bonds and cellulose(NCC,CNF)were added to the polyacrylamide and acrylamide gel systems to enhance the mechanical strength of the gel valves.The effects of different nanoparticles on tensile properties,compressive properties and viscoelastic properties of the composite gels were studied by texture analyzer and rheometer,and scanning electron microscopy(SEM),Fourier transform infrared spectroscopy(FTIR)and solid-state nuclear magnetic resonance(SSNMR)were used to explore the mechanism of nanoparticle reinforced composite gel.The results showed that,for polyacrylamide gel,the mechanical strength of composite gel could be effectively enhanced by adding microspheres to the system.In contrast to the gel without microsphere,the tensile stress of composite gel containing 10wt% microsphere was increased by about twenty times,and the compressive stress was about 1400 kPa,which was almost three times larger than the gel without microsphere.For the acrylamide / AM/HEMA microspheres composite gel,when the ratio of acrylamide to microspheres was 6:2,the tensile stress of the composite gel was the greatest and the proportion of tension was fine,which indicated that the gel had excellent toughness.When the ratio of acrylamide to microspheres was 7:1,the compressive stress and elasticity moduli of the composite gel were the largest.After compression,composite gel could almost recover its original shape,with a little ring-cut broken occurred,while the gel without microsphere cracked in large area,which indicated that the elasticity of the composite gel was improved.Scanning electron microscopy(SEM)results showed the gel enveloped the spherical particles,which increased the thickness of the pore wall of the gel,and the microspheres had great elasticity,so the mechanical properties of the composite gel were obviously improved.For the acrylamide / polymerizable microspheres composite gel,when the ratio of acrylamide to polymerizable microspheres was 6:2,the mechanical properties of the composite gel reached the best.During the compression process,the composite gel completely restored to its original state without breakage.The composite gel showed unique honeycomb network structure with microsphere as "crosslinking point",FTIR and SSNMR results showed that the double bonds on the surface of polymerizable microspheres reacted with acrylamide monomer to form such unique network structure.For acrylamide / cellulose composite gel,when the ratio of acrylamide to nano cellulose NCC and CNF was 5:3,the mechanical properties of composite gel were the best.The toughness enhancement of NCC composite gel was more obvious;the strength enhancement of CNF composite gel was more significant,the tensile stress was nearly six times higher than that of the gel without cellulose.