Synthesis Of Copolymer Nanocomposite Drag Reducer And Its Drag Reduction Performance And Development Of Fracturing Fluid

In the development of tight oil and gas reservoirs,slick-water fracturing is an efficient method of reservoir reconstruction,in which drag reducer is an important additive.The drag reduction performance has a significant impact on hydraulic fracturing.With the more application of hydraulic fracturing in the complex geological condition,it is essential to improve the comprehensive performance of drag reducer.In addition,with the increasing awareness of environmental protection,fracturing fluids and flowback fluids are required to be low-residue,environmentally friendly,nontoxic,easy handling and low damage to the reservoir.Therefore,the research on new drag reducers has always attracted the attention of experts and scholars in the petroleum industry.In this paper,nanomaterials are introduced into polymer matrix to prepare nanocomposite drag reducers,in which uniform nanophase dispersion is achieved through molecular structure design.The drag reduction characteristics are studied by both indoor experiments and numerical simulation.Finally,a fracturing fluid is prepared by nanocomposite drag reducer.The main research results are as follows:（1）The nucleophilic substitution reaction between allyl bromide and dimethylhexadecyl amine is used to prepare hydrophobic monomer（Dimethylhexadeylallylammonium bromide,DMHAAB）.The original sodium-based montmorillonite is modified with a cationic surfactant to prepare intercalated nanophase intermediates,and the interlayer spacing expands from 1.22 nm to 2.10 nm.Nanocomposite drag reducer（ASD/MMT）is prepared by in-situ polymerization with acrylamide（AM）,sodium p-phenylethylsulfonate（SSS）,DMHAAB and modified montmorillonite.The characteristic peak of modified montmorillonite in XRD spectrum disappears.Observed by transmission electron microscope（TEM）,it is found that the montmorillonite lamellae exhibit the disordered exfoliation state in the polymer matrix.The scanning electron microscope（SEM）technique shows a three-dimensional network structure that closely connects to montmorillonite exfoliated layers with the polymer matrix.Montmorillonite interacts with the polymer matrix,which provides a structural basis for improved performance.Compared with pure polymer（ASD）,ASD/MMT is superior to ASD in terms of salt resistance,temperature resistance and viscoelasticity.The experimental results show that the drag reduction performance of ASD/MMT is better than that of ASD under the same condition.（2）Functional nano-phase material is prepared by surface modification of nano-silica,and the nanocomposite drag reducer（PASD-Si O₂）is synthesized using other monomers.SEM shows that nano-silica particles are uniformly dispersed in the polymer matrix,and the molecular microscopic network structure of PASD-Si O₂ is denser.This structure weakens the influence of harsh external environment（high temperature,high salinity and high shear）on its stability.For the same solution,the viscosity of PASD is significantly lower than that of PASD-Si O₂ after shearing at 90℃for 53 min.The drag reduction experiment results show that compared with PASD,the drag reduction performance of PASD-Si O₂ is improved to some extent.Monovalent cations（Na⁺）have less effect on the PASD-Si O₂ drag reduction performance in comparison with divalent cation(My²⁺).When the sample solution with a concentration of 0.05%is sheared for 30min at a high pump speed,the drag reduction rate is 11.12%higher than that of PASD.（3）Based on the viscoelastic theory and nanocomposite characteristics,a geometric model corresponding to the experimental pipe,and a model combined rigid and flexible molecules constitutive relationship are established.The program is implanted into ANSYS FLUENT by the user-defined function.Numerical simulation results are relatively close to experimental results.Within a certain range,the drag reduction rate rises with the increase of parameters such as Reynolds number,Weissenberg number and stretch length of the molecule.（4）By optimizing the type and concentration of drag reducer,clay anti-swelling agent and surfactant,the formulation of nanocomposite fracturing fluid is 0.07%ASD/1%MMT,1%KCl and 0.01%TF328.The fracturing fluid has the advantages of low surface tension,low interfacial tension,easy flowback,environmental protection and stable drag reduction performance.The surface/interfacial tension of the nanocomposite fracturing fluid remains stable after being placed in 80°C for 4 h.Drag reduction performance and shear resistance of nanocomposite fracturing fluid are better than hydroxypropyl guar gum.A qualitative analysis of the nanocomposite drag reduction mechanism is carried out.The nanocomposite drag reducer has both the flexibility of the polymer and the rigidity of the nanophase.The flexibility can provide high drag reduction,and the rigidity can improve the structural stability.The drag reducer provides a new type of material for slick water fracturing.