Study On Random Copolymer Emulsifier And Nanocomposite Emulsion For Oil Recovery

At present,the exploitation of low-permeability reservoirs in China is the main source of increased production.However,their exploitation is often associated with low in development efficiency and poor recovery after water flooding.In order to develop high-efficiency oil displacement systems required for medium and low permeability reservoirs,two kinds of(anionic and nonionic)random copolymer emulsifiers were designed and synthesized.Using the random copolymer emulsifier and two-dimensional nanomaterials(surface modified montmorillonite and laponite),composite nanoemulsions were successfully prepared and then the flooding tests in medium and low permeability cores were conducted using the composite nanoemulsions as the enhanced oil recovery(EOR)agent.The main results of the research are as follows:(1)Design and synthesis of anionic and nonionic random copolymer emulsifiersAnionic amphiphilic random copolymers with sodium p-styrene sulfonate(SSS)and dodecyl methacrylate(LMA)side chains and nonionic amphiphilic random copolymers with poly(ethylene glycol)methyl ether methacrylate(PEGMA;Mn = 475,950)and dodecyl methacrylate(LMA)side chains were synthesized.The p(SSS)-ran-p(LMA)have very high thermal stability and the degradation temperature is greater than 300°C.After the addition of salt,the surface activity of the anionic polymer p(SSS)-ran-p(LMA)aqueous solution is enhanced due to the reduction of electrostatic repulsion.However,the salt addition has a negligible effect on the surface activity of the nonionic polymer p(PEGMA)-ran-p(LMA)solution.(2)Preparation of negatively charged composite nanoemulsion by using P(SSS)-ran-P(LMA)and layered silicate(modified montmorillonite or laponite)Negatively charged O/W nanoemulsions were first prepared by phase inversion composition method(PIC)at 70 °C using the anionic copolymer p(SSS)-ran-p(LMA)and nonionic surfactant Brij 30 as a co-stabilizers and liquid paraffin as oil phase.Then,two-dimensional particle emulsifiers(modified montmorillonite or laponite)were added to the nanoemulsion formula to prepare O/W composite nanoemulsions.Dynamic light scattering(DLS)and transmission electron microscopy(TEM)results show that the negatively charged O/W nanoemulsions have very narrow particle size distribution.As the hydrophilic/hydrophobic group mass ratios increase from 5/7 to 4/2,the average particle size(Z-Ave)of the nanoemulsions gradually increased from 47 nm to 65 nm.After adding a small amount of salt(?0.05 MNa Cl),the oil-water interfacial tensions are significantly reduced and the phase inversion temperature of the nanoemulsions are still greater than 90 °C.After adding modified montmorillonite(or laponite)platlets,the particle size and the absolute value of zeta potential of the composite nanoemulsions increase.Particle size analysis shows that the negatively charged(composite)nanoemulsions have good long-term stability.(3)Preparation of positively charged composite nanoemulsion by using p(PEGMA)-ran-p(LMA)and layered silicate(modified montmorillonite or laponite)Positively charged O/W nanoemulsions were first prepared by phase inversion composition method(PIC)at 70°C using the nonionic copolymer p(PEGMA)-ran-p(LMA),nonionic surfactant Brij 30 and cationic dimethylene-1,2-bis(hexadecyldimethylammonium bromide)surfactant(G16-2-16)as co-stabilizers and liquid paraffin as oil phase.Then,a two-dimensional particle emulsifier(modified montmorillonite or laponite)is added to the nanoemulsion to prepare O/W composite nanoemulsion.Dynamic light scattering(DLS)and transmission electron microscopy(TEM)results show that the molecular weight of the hydrophilic monomer of the polymer emulsifier has a great influence on the particle size of the nanoemulsions.The nanoemulsion prepared with p(PEGMA950)-ran-p(LMA)has a particle size of about 40-55 nm,while the average particle size of nanoemulsion prepared with p(PEGMA475)-ran-p(LMA)was about 25 nm.After adding a small amount of salt(?0.05 MNa Cl),the oil-water(nanoemulsion is external phase)interfacial tension is significantly reduced,and at the same time the phase transition temperature of the nanoemulsion also reduced.After adding modified montmorillonite and laponite,the average particle size and zeta potential of the nanoemulsion increased.Particle size analysis shows that all the positively charged(composite)nanoemulsions have very good long-term stability.(4)The oil displacement behavior of nanocomposite emulsion on medium-low permeability core was studiedBased on the above research,six sets of nanoemulsion formulations are screened and prepared with 0.02 MNa Cl brine and the nanoemulsion was diluted 5 fold.Core flooding experiment in medium-low permeability cores(about 16?200 m D)are carried out using 0.02 MNa Cl brine and followed by using the diluted nanoemulsion as flooding fluids.The results show that in the medium permeability core,the positively charged nanoemulsion systems enhanced the recovery by 5?6% compared with the brine flooding.In the medium permeability core,the negatively charged nanoemulsion systems enhanced the recovery by 10?23.5% compared with the brine flooding.The latter has a higher oil displacement efficiency.In low-permeability core(16.7 m D),the laponite negatively charged nanoemulsion system improves the recovery by 25% compared with the brine flooding.The oil displacement enhancement is remarkable.