Abstract
A new type of chitosan-modified hyperbranched polymer (named HPDACS) was synthesized through the free-radical polymerization of surface-modified chitosan with acrylic acid (AA) and acrylamide (AM) to achieve an enhanced oil recovery. The optimal polymerization conditions of HPDACS were explored and its structure was characterized by Fourier-transform infrared spectroscopy, hydrogen nuclear magnetic resonance, and environmental scanning electron microscopy. The solution properties of HPDACS in ultrapure water and simulated brine were deeply studied and then compared with those of partially hydrolyzed polyacrylamide (HPAM) and a dendritic polymer named HPDA. The experimental results showed that HPDACS has a good thickening ability, temperature resistance, and salt resistance. Its viscosity retention rate exceeded 79.49% after 90 days of aging, thus meeting the performance requirements of polymer flooding. After mechanical shearing, the viscosity retention rates of HPDACS in ultrapure water and simulated brine were higher than those of HPAM and HPDA, indicating its excellent shear resistance and good viscoelasticity. Following a 95% water cut after preliminary water flooding, 0.3 pore volume (PV) and 1500 mg/L HPDACS solution flooding and extended water flooding could further increase the oil recovery by 19.20%, which was higher than that by HPAM at 10.65% and HPDA at 13.72%. This finding indicates that HPDACS has great potential for oil displacement.
Highlights
As a tertiary oil recovery technology, polymer flooding has become one of the most mature and effective strategies for enhanced oil recovery (EOR) [1,2,3,4,5]
The structure of hyperbranched polymer based on modified chitosan (HPDACS) (Figure 10c) is different from those of hydrolyzed polyacrylamide (HPAM) and HPDA: the framework connecting the aggregates is thicker, the network structure is more compact, the cavity of physical network structure is more uniform, and the membrane formed is more conducive to improve the structure strength of HPDACS. This result is mainly because the modified chitosan monomer and branched monomer in HPDACS formed a dense and structured dendritic skeleton, and the chitosan structure enhances the rigidity of polymer molecular chains to a certain extent, forms some membranes and improves the temperature and shear resistance of the polymer to a certain extent
When the polymer concentration increased to 3000 mg/L, the viscosity of HPDACS was 41.3 mPa·s, which was higher than the 37 mPa·s of HPAM and 26.3 mPa·s of HPDA
Summary
As a tertiary oil recovery technology, polymer flooding has become one of the most mature and effective strategies for enhanced oil recovery (EOR) [1,2,3,4,5]. The hyperbranched polymer has a highly branched 3D structure, a number of terminal functional groups, high chemical reactivity, and good solubility and has received increasing interest [17,18,19,20,21,22]. Introducing chitosan into a high-molecular polymer chain as an oil displacing agent may improve the biodegradability of the polymer to reduce environmental pollution. Solution properties, including solubility, thickening ability, temperature and salt resistance, shear resistance, antiaging performance, and viscoelasticity, were compared among HPDACS, the dendritic polymer (HPDA), and HPAM. Their EOR performances were evaluated by core-flooding experimentation
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