Hydrophobic Modification Of Cellulose Nanofibers And The Application In Oil Field Leakage Sealing

Tempo-oxidized cellulose nanofibers(TOCNF)is a gelatinous substance obtained by combining oxidized plant fibers with mechanical treatment.TOCNF has the advantages of special gel properties,huge specific surface area,high reactivity and high mechanical strength,and can be used as an ideal functional material to enhance the strength of hydrogel.However,the surface function group of TOCNF is carboxyl group,and the heat resistance of the gel decreases and the gel becomes thin at high temperature,which limits its application in high temperature environment.In this paper,functional hydrophobic modification of TOCNF is carried out,hydrophobic groups are introduced on the surface of the fiber,and the heat resistance of the gel is improved by using the principle of hydrophobic association.In addition,modified TOCNF is used as synergist of polymer gel to improve the heat resistance and mechanical properties of the composite gel,so as to prepare the composite hydrogel with high mechanical properties.And explore its potential application value as oil field plugging material.The main research contents and achievements are as follows:1.Firstly,under the condition of CTAB as catalyst,the green reagent dimethyl carbonate was used to hydrophobically modify TOCNF.The methyl group of dimethyl carbonate(DMC)was grafted to the surface of TOCNF to obtain DMC-TOCNF.When the addition amount of DMC was 250%(relative to the absolute dry TOCNF),The maximum substitution degree is 0.630,and the viscosity increases from 2369 m Pa·s to 2.9×104 m Pa·s when the temperature rises from 30℃ to 160℃.On the contrary,TOCNF decreased from2369 m Pa·s to 167 m Pa·s.It is proved that DMC modification endows TOCNF with high temperature gel properties and improves its gel heat resistance.Secondly,DMC-TOCNF was mixed with acrylamide(AM)and N,N-dimethyl acrylamide(DMAA)to prepare DMC-TOCNF composite hydrogel by in situ polymerization.A stable hydrogel was formed between DMC-TOCNF and polymer bond through physical entanglement and hydrogen bonding.Mechanical tests proved that DMC-TOCNF enhanced the strength of hydrogel.2.On the basis of methylation modification,ASA-TOCNF with double bond and hydrophobic long chain was obtained by using the double bond dry enyl succinate(ASA)to modify TOCNF.When the amount of ASA was 200%(compared with the absolute dry TOCNF),the substitution degree of ASA-TOCNF reached the maximum,and ASATOCNF also had high temperature gelatinization.Then,ASA-TOCNF was mixed with N,N-dimethylacrylamide(DMAA)and AM to prepare ASA-TOCNF-based hydrogels through polymerization.Through the double bond on the side chain of ASA-TOCNF,a covalent cross-link is formed between TOCNF and polymer bond,and a more stable hydrogel structure is formed.It was found that the tensile and compressive strength were 3 times and2.8 times higher than the original hydrogel,respectively.In addition,the ASA-TOCNF enhanced hydrogels were tested for aging and compression under a simulated oilfield environment(110℃,2 wt% salt concentration),and the results showed that the hydrogels had good decomposition resistance and gel strength.3.P(AM-co-DMAA)/TA/ASA-TOCNF composite hydrogel was prepared by in-situ polymerization of ASA-TOCNF,Tannic acid,AM and DMAA.It was found that when the addition amount of TA was 20 wt% and the addition amount of ASA-TOCNF was 1 wt%,the mechanical test showed that P(AM-co-DMAA)/TA/ASA-TOCNF had higher strength and toughness,and the tensile strength was 3.3 times higher than that of traditional hydrogel.At the same time,the aging and texture tests of P(AM-co-DMAA)/TA/ASATOCNF hydrogel under simulated oilfield environment(130℃,5 wt% salt concentration)showed that the hydrogel had good decomposition resistance and gel strength.