Preparation And Properties Of PH-responsive Acrylamide Polymer Thickeners With Cucurbituril Side Groups

Acidizing is an effective method for carbonate reservoir reconstruction,which make use of acid to achieve the purpose of removing blockage,building fissure,opening the flow channel of oil and gas,and improving reservoir permeability.Since the fast reaction rate between the acid and carbonate formation has a great influence on the penetration distance of acid in acidizing treatment,thickening agent is added to increase the viscosity of acid,thereby reducing the filter loss rate and decreasing the acid-rock reaction rate.Acrylamide polymers are widely used as acid thickeners,and its good performance has very important significance for oil well stimulation.This paper is studied on the basis of domestic and foreign research,a novel monomer acrylic cucurbit[7]uril ester(ACE)is obtained by modifying supramolecular cucurbit[7]uril,and then ACE is utilized to react with acrylamide(AM)and 2-acrylamido-2-methylpropanesulfonic acid(AMPS)to synthesize P(AM/ACE/AMPS).The introduction of cucurbit[7]uril rigid structure can improve the temperature resistance and salt tolerance of copolymer,and its special structure and host-guest chemistry effect can result in the pH-response of this novel acrylamide polymer acid thickener.The details are as follows:(1)Microwave preparation and optimization of glycoluril,cucurbit[7]uil and perhydroxycucurbit[7]uil.Glycoluril is synthesized by carbamide and oxaladehyde under power 80W and acid conditions,the reaction time is reduced to 0.5-2min compared to the traditional preparation of 4-5h.Cucurbit[7]uril is synthesized through condensation polymerization of glycoluril and formaldehyde,its reaction time is reduced to 0.5-7min from 10-12h,and its optimum reaction conditions are tested by the single factor experiment and response surface methodology:80W of power,2.2 of mass ratio,3.74M of hydrochloric acid concentration.Then cucurbit[7]uril is directly oxidated to perhydroxycucurbit[7]uil by potassium persulfate under power 80W,and its reaction time is reduced to 1-5min from 6-7h.Finally,ACE is prepared through esterification reaction of perhydroxycucurbit[7]uil and acrylic acid.(2)P(AM/ACE/AMPS)is synthesized by AM,ACE and AMPS through redox free-radical polymerization,the optimum copolymerization conditions are tested by the single factor experiment:45 ℃ as reaction temperature,5h as reaction time,0.06wt%of initiator dosage,20wt%of total monomer concentration,1.8wt%of AMPS content and 0.14wt%of ACE content.The response surface methodology is employed to confirm the optimum conditions on the basis of single factor experiment,which conditions are:44.84℃ as reaction temperature,20.67wt%of total monomer concentration,0.063wt%of initiator dosage.The structure of P(AM/ACE/AMPS)is characterized by FT-IR and 1H NMR,and its weight-average molecular weight(2.36×106g/mol)is measured by SLS.Bipolymer P(AM/AMPS)is synthesized on the same conditions as P(AM/ACE/AMPS),their viscosity-average molecular weights are determined as 2.55×106g/mol and 1.97×106g/mol respectively.Then their microstructures are compared through SEM,and their thermal properties are investigated by TG.(3)The performances of P(AM/ACE/AMPS)and P(AM/AMPS)are evaluated according to the People’s Republic of China oil and gas industry standards SY/T 6214-1996 " Evaluation Method of acid thickener".Their performances are compared in aspects of rheological property,thermal stability,shear stability,retarding property and acid resistance,meanwhile,the influence of cucurbit[7]uril structure on the performance of gelled acid has been studied.The pH-response mechanism can be explained as follows:the special structure of cucurbit[7]uril can form protonated network structure with AMPS in acid solution,and it can also form metal ion-cucurbit[7]uril complex frame structure through host-guest coordination,the above two structures can effect on the variation of structure of P(AM/ACE/AMPS),thereby causing the variation of viscosity and resulting in the pH-response of P(AM/ACE/AMPS).Experimental study demonstrates this novel acid thickener owns good viscosified property,thermal stability,shear stability retarding property and compatibility,moreover,its pH-response can cause the viscosity first rising then decreasing followed by the decrease of acid concentration.The superior performances of P(AM/ACE/AMPS)revealed a potential application as acid thickener for acidizing treatment.