A Hydroxypropyl Methyl Cellulose-Based Graft Copolymer with Excellent Thermothickening and Anti-salt Ability for Enhanced Oil Recovery

Abstract

Thermothickening polymers are a novel type of material developed for enhanced oil recovery applications in high-temperature and high-salinity oil reservoirs. However, the existing synthesis process of thermoviscosifying polymers is complex and of high cost, both of which limit the wide application of thermoviscosifying polymers. In this study, a thermothickening water-soluble polymer (PHAD) with a low concentration was synthesized by a “graft from” method, with acrylamide and diacetone acrylamide as grafted monomers and hydroxypropyl methyl cellulose as the backbone chain. The basic parameters for PHAD copolymers were systematically studied in comparison with their homopolyacrylamide counterpart. The results show that the PHAD copolymers exhibited excellent thermothickening ability even when the polymer concentration was 0.2 wt % (total salinity is 9350.08 mg·L–1) upon increasing the temperature from 25 to 90 °C, where the apparent viscosity enhancement changes from 4.0 to 13.3 times with increasing the diacetone acrylamide content in PHAD copolymers. The PHAD copolymers also showed good salt tolerance, thermal stability, and viscoelastic properties under harsh reservoir conditions, which are attributed to the synergistic effect of the rigid heterocyclic ring structure and hydrophobic intermolecular association of thermoresponsive monomers within polymer chains. Moreover, the core displacement experiment and etched glass microscopic model show that the PHAD copolymers have good migration in porous media. Due to its high sweep efficiency, the PHAD copolymer has a higher recovery factor (14.0%) than polyacrylamide (4.3%), which makes it more suitable for salt-tolerant and temperature-tolerant tertiary oil recovery chemicals.

Stability and Rheological Properties of the Hydroxypropyl Methyl Cellulose-Based Graft Copolymer/Halocynthia roretzi Drasche-Based Cellulose Nanocrystal/Sodium Dodecyl Sulfate Dispersion for Enhanced Heavy Oil Recovery

“…In PHAD copolymer, the absorption peaks at 1674 cm –1 were related to carbonyl groups, which became more stretched after the addition of TCNCs and moved to a lower wavenumber with the increase of TCNCs (1674, 1665, and 1658 cm –1 ), indicating the formation of hydrogen bonds between the PHAD copolymer and TCNCs. , The FTIR spectroscopy of PHAD/SDS/TCNCs dispersions in simulated brine solution was shown in Figure b. and it can be seen that the addition of salt also made the absorption peaks at 1661 cm –1 of carbonyl groups stronger and also move to a lower wavenumber (from 1661 to 1652 cm –1 ) in brine, which is because the polar circumstance brought by salts strengthens the interaction among polymer chains; therefore, more intra- and intermolecular hydrogen bonds were formed …”

“…It is known that the hydrogen-binding interactions will become weaker while the hydrophobic association can be strengthened with the increase of the temperature. ,, Thus, the thermothickening ability of the dispersions may mainly originate from the hydrophobic associations. The PHAD copolymer contains a thermally sensitive HPMC backbone as well as DAAM side chains, and there are strong intra- and intermolecular hydrophobic interactions between the PHAD copolymers and SDS micelles, which contribute to a significant improvement in apparent viscosity (Scheme b). In addition, the hydrophobicity of the thermally sensitive polymer chains becomes stronger and stronger with the increase of the temperature, so that the hydrophobic associations transcend the free motion of the power of chains, resulting in a sharp augment of the apparent viscosity .…”

“…The PHAD copolymer contains a thermally sensitive HPMC backbone as well as DAAM side chains, and there are strong intra- and intermolecular hydrophobic interactions between the PHAD copolymers and SDS micelles, which contribute to a significant improvement in apparent viscosity (Scheme b). In addition, the hydrophobicity of the thermally sensitive polymer chains becomes stronger and stronger with the increase of the temperature, so that the hydrophobic associations transcend the free motion of the power of chains, resulting in a sharp augment of the apparent viscosity . Moreover, it is found that the apparent viscosity of the dispersions increases regularly along with an elevated amount of TCNCs.…”

“…19,20 Therefore, we synthesized a kind of graft copolymer named PHAD using hydroxypropyl methyl cellulose (HPMC) containing a rigid six-membered heterocyclic structure, which had a relatively superior temperature and salinity resistance performance in hard reservoir conditions. 20 In the past few years, nanomaterials have attracted comprehensive attention in the petroleum industry owing to their superior characteristics and performance, including high specific surface area and surface energy, small size effect and quantum size effect, etc. 21−23 The practical applications of a variety of nanoparticles, such as SiO 2 , 24,25 TiO 2 , 26 ZrO 2 , 27 and Fe 3 O 4 , 28 have concentrated on reservoir characterization, nanotracking, well drilling, and enhanced oil recovery (EOR).…”

“…In aqueous solution, PAM tends to hydrolyze and transform into partially hydrolyzed polyacrylamide (HPAM) with abundant carboxyl groups, which can lead to the viscosity enhancement of displacing fluid. , However, the practical application of PAM-based polymers is obstructed in reservoirs with harsh conditions (high temperature, high salinity, pressure, and bacteria), because PAM-based polymers usually degrade and hydrolyze in high-temperature and high-salinity conditions, leading to the destruction of the network structure and the production of a toxic acrylamide monomer. , Moreover, carboxylate groups incline to interact with metal ions, generate precipitation in the formation water, and in turn, cause viscosity reduction and recovery efficiency diminishment. − Therefore, various methods, such as the introduction of different functional groups, such as hydrophobic groups, − have been used to improve the chemical stability and temperature/salt tolerance of PAM-based polymers. In addition, natural polymers, such as cyclodextrin, xanthan gum, and chitosan, contain a rigid structure, which plays a significant role in thermostability enhancement, thereby improving oil recovery efficiency. , Therefore, we synthesized a kind of graft copolymer named PHAD using hydroxypropyl methyl cellulose (HPMC) containing a rigid six-membered heterocyclic structure, which had a relatively superior temperature and salinity resistance performance in hard reservoir conditions …”