Preparation Of Nanocellulose Based Temperature And Salt Resistant Water Plugging Hydrogel And Investigation Of Water Control Mechanism

Fractured-vuggy carbonate reservoirs are widely distributed and have huge reserves.After years of water drive development,they have shown the characteristics of low water drive response and recovery.The polymer pre-crosslinked hydrogel expanded while encountering water and has excellent plugging performance.However,most of the hydrogels were polyacrylamide based and not have multifunctional properties.Especially at high temperatures,high salt,and high pressure environment,the structure of the hydrogel could be broke and lost the plugging effect while the hydrogel expanded.Therefore,it is important to develop multifunctional hydrogel plugging agents with unique properties such as temperature resistance,high salt resistance,high toughness,slow expansion,and self-healing for expanding the intelligent plugging of oil fields.In this paper,we used cellulose nanofiber combined with polyamine,polyvinyl alcohol,and tannin to polymerize functional hydrogel with temperature and salt resistance performance.This research could provide a new idea for efficient water plugging in carbonate reservoirs.Aldehydeized cellulose nanofibers(DA-CNF)were obtained by sodium periodate oxidation.The temperature and salt-resistant double network hydrogel was produced by photoinduced radical polymerization using acrylamide(AM)and2-acrylamide-2-methylpropane sulfonic acid(AMPS)as polymerization monomers,DA-CNF,and polyether amine as reinforcing agents.The results showed that the oxidized DA-CNF was still fibrous,and add DA-CNF could significantly improve the mechanical strength of the double network hydrogel.When the hydrogel with 3.00 wt%addition,after aging for 16 days at 10.0×10~4mg/L saline environment and 130℃,the hydrogel structure remained unaltered.An intelligent multi-network plugging hydrogel particle-which was prepared by AM as the chemical crosslinking base material,polyvinyl alcohol(PVA),DA-CNF and tannic acid(TA)as the functional additives.The obtained hydrogel particles could crosslinked again in a high temperature and high salt environment.The results show that DA-CNF and PVA can improve the physical strength of hydrogel significantly.Moreover,the added TA enabled the hydrogel particles ability to re-crosslink in high-salt and high-temperature environments which containing calcium and magnesium ion.The hydrogel particles cannot be re-crosslinked in clean water,but when the solution contains salt and high valence ions,the particles re-crosslinked.The hydrogel particles with 20.0 wt%TA can be re-crosslinked in 36 h at 130~oC,21.0×10~4mg/L saline solution,with a calcium and magnesium ion content of 1.00×10~4mg/L.After 60days of aging,the elastic modulus G′of hydrogel can still be maintained at 206 Pa,and the structure can still maintain a porous three-dimensional network.Re-crosslinked hydrogel plugging agent can provide a new idea for the intelligent plugging of high-temperature and high-salinity reservoirs.Because of the rapid expansion rate of traditional pre-crosslinked hydrogel particles,a temperature-sensitive gel plugging agent(UCST)was prepared by using hydrophobic PVA temperature-sensitive characteristics,hydrophobic modification of PVA,DA-CNF reinforcement agent,and glutaraldehyde crosslinked.Using the advantage of the gradually rising oilfield formation temperature characteristics,hydrogel plugging agent particles achieve the effect of“shrinkaged at low-temperature and easily to inject,expanded at high-temperature and pluging.”The results showed that when the PVA concentration is 10.0%,furfural 4.50%or 5.00%,glutaraldehyde5.00%,and DA-CNF 2.00 wt%,the prepared temperature-sensitive particles have excellent mechanical properties,delayed expansion,temperature resistance,and salt resistance characteristics.The initial plugging efficiency at room temperature is about75.0%,reaching over 87.0%after 4 days at 90~oC,with a maximum of 93.4%.The migration behavior of a single expanded hydrogel particle(PPG)in a single throat was studied to reveal the migration mechanism of hydrogel particles in the process of water plugging.The results show that when a single PPG particle passes through a single throat,the pressure difference at both ends of the throat increases with the increase in the deformation of hydrogel particles and decreases with the recovery of deformation;The ratio of hydrogel particles size to throat diameter significantly affects the fluctuation of the pressure difference curve at both ends of the throat.The peak pressure difference at both ends of the throat increases with the increasing Dg/Dp,which shows a power function relationship.