Preparation Of Lignin-based Oilfield Plugging Agent And Its Temperature And Salt Tolerance

Lignin,as one of the three components of plant resources,mainly comes from the by-products of pulp and paper industry.It has the characteristics of non-toxic,biodegradable and low price,but it has a low value utilization rate.Lignin is mainly a macromolecule composed of phenylpropane structure,which has good thermal stability and can be applied in a variety of high temperature environments.In recent years,with the increase of oil exploitation depth,high temperature and high salt have become the main characteristics of formation environment.Therefore,conventional polymer plugging agent can not meet the existing needs,and lignin can be used as an ideal material in the design of oilfield water plugging material.Although lignin and its modifiers have been used in oilfield exploitation for many years,there are few studies on lignin as water shutoff agent.Most of the applications and studies have been mainly lignin sulfonate,and there are few reports on the crosslinking curing,temperature and salt resistance of lignin.In this study,phenolic hydroxyl,methoxy and other groups in lignin structure were used to crosslink and solidify lignin,and explore the application of lignin in high temperature and high salt environment.The main research contents and results are as follows:1.Dialdehyde cellulose nanofibers(DA-CNF)were applied to lignin hydrogels.The strength of lignin hydrogels was enhanced by the interpenetrating network of DA-CNF in hydrogels and the condensation reaction between aldehyde group and alkali lignin phenolic hydroxyl group.Fourier transform infrared spectroscopy(FTIR)showed that polyethylene glycol diglycidyl ether(PEGDGE)and DA-CNF reacted with lignin.Scanning electron microscope(SEM)analysis showed that the structure of lignin hydrogel was porous after adding DA-CNF.The addition of DA-CNF can significantly improve the physical strength,thermal stability,temperature and salt resistance of lignin hydrogels.When the amount of DA-CNF is 2.0%,the tensile strength increases from 69.0 k Pa to 175 k Pa,and the compressive stress increases from 0.18 MPa to 1.5 MPa;The initial degradation temperature increased from 209℃to 248℃.DA-CNF reinforced lignin hydrogel has high temperature and salt resistance.After aging for 20 days in salt water with a salinity of 200000 at 150℃,the yield of DA-CNF reinforced lignin hydrogel can still retain 86.4%and has good p H adaptability.2.The carboxyl cellulose nanofibers(DA-TOCNF)modified by dialdehyde were crosslinked and polymerized with lignin to form a multi network crosslinked lignin hydrogel,so as to enhance the physical strength of lignin hydrogel.Firstly,the amination modification of lignin and its performance characterization were explored.The results showed that when the temperature was 60℃and amine:aldehyde=1:2,FTIR showed that amino groups were successfully connected to lignin.The nitrogen content of Lignin Amine was 5.49%by elemental analysis;The results showed that adding DA-TOCNF could significantly improve the physical strength,temperature and salt resistance of Lignin Amine hydrogel.When the amount of DA-CNF is 2.0%,the tensile strength increases from 79.0 k Pa to 208 k Pa,and the compressive stress increases from 0.18 MPa to 0.42 MPa.After the cured Lignin Amine gel is aged for 60 days in salt water with a salinity of 210000 at 150℃,the gel can still maintain a complete external morphology.The mass retention rates of 0 wt%and 2 wt%DA-TOCNF lignin can reach 46.2%and 55.16%respectively,and the aged lignin hydrogel can still have very strong compressive mechanical properties.3.Generally,amines are the common curing agent of epoxy resin.In this part,epoxy resin(EP)is used as the curing agent of amine modified lignin.Epoxy resin/Lignin Amine gel not only has excellent mechanical and high-temperature curing properties of epoxy resin,but also has good thermal stability of lignin.The results show that with the increase of EP addition,the mechanical strength first increases and then decreases,and the initial temperature gradually decreases.When the addition of EP reaches 100%,the tensile stress of lignin/epoxy resin reaches the maximum,which is 0.94 MPa.The results of high temperature aging test show that the epoxy resin/Lignin Amine gel still maintains excellent mechanical properties and the overall structure is still complete after aging in 150~oC and210000 salinity brine for 60 days.In addition,according to the mass ratio before and after aging,the maximum mass retention rate can reach 71.29%.The review shows that epoxy resin and amine lignin can form a compound with temperature resistance,salt resistance and high strength,which has potential application value in high temperature oil and gas fields.