Abstract
Polymeric nanoparticle suspension is a newly developed oil-displacing agent for enhanced oil recovery (EOR) in low-permeability reservoirs. In this work, SiO2/P(MBAAm-co-AM) polymeric nanoparticles were successfully synthesized by a simple distillation–precipitation polymerization method. Due to the introduction of polymer, the SiO2/P(MBAAm-co-AM) nanoparticles show a favorable swelling performance in aqueous solution, and their particle sizes increase from 631 to 1258 nm as the swelling times increase from 24 to 120 h. The apparent viscosity of SiO2/P(MBAAm-co-AM) suspension increases with an increase of mass concentration and swelling time, whereas it decreases as the salinity and temperature increase. The SiO2/P(MBAAm-co-AM) suspension behaves like a non-Newtonian fluid at lower shear rates, yet like a Newtonian fluid at shear rates greater than 300 s−1. The EOR tests of the SiO2/P(MBAAm-co-AM) suspension in heterogeneous, low-permeability cores show that SiO2/P(MBAAm-co-AM) nanoparticles can effectively improve the sweep efficiency and recover more residual oils. A high permeability ratio can result in a high incremental oil recovery in parallel cores. With an increase of the permeability ratio of parallel cores from 1.40 to 15.49, the ratios of incremental oil recoveries (low permeability/high permeability) change from 7.69/4.61 to 23.61/8.46. This work demonstrates that this SiO2/P(MBAAm-co-AM) suspension is an excellent conformance control agent for EOR in heterogeneous, low-permeability reservoirs. The findings of this study can help to further the understanding of the mechanisms of EOR using SiO2/P(MBAAm-co-AM) suspension in heterogeneous, low-permeability reservoirs.
Highlights
In recent years, due to the severe heterogeneity of reservoir formations, serious water channeling has become a well-recognized problem in the development of low-permeability reservoirs, as the reservoirs enter into the middle or late stages of waterflooding development [1,2,3,4]
Lai et al synthesized modified nano-SiO2/AA/AM copolymer (HPMNS) oil displacement agents by free-radical polymerization and carried out indoor displacement tests, and the results indicated that the copolymers can increase both the resistance factor and residual resistance factor in a medium-porous medium under a similar permeability, and they have a stronger mobility control capacity that can effectively improve the enhanced oil recovery (EOR) [40]
SiO2/P(MBAAm-co-AM) composite nanoparticles have been successfully synthesized by a distillation–precipitation polymerization method
Summary
Due to the severe heterogeneity of reservoir formations, serious water channeling has become a well-recognized problem in the development of low-permeability reservoirs, as the reservoirs enter into the middle or late stages of waterflooding development [1,2,3,4]. Liu et al fabricated a novel, star-like, hydrophobically associative polyacrylamide (SHPAM) used in EOR processes in harsh reservoir conditions, and core flooding tests revealed that SHPAM at a concentration of 1500 mg/L increases the oil recovery factor by 20% in sandstone cores [43] It can be seen from the above references that these polymeric nanoparticle suspensions used in high-permeability reservoirs rely on high viscosity to improve the mobility ratio of fluids, which can realize conformance control to improve the EOR. They cannot be injected into or move through a porous medium in low-permeability reservoirs. The synthetic formation water used for the displacement experiments was a brine with a total dissolved solids (TDS) value of 5380 mg/L
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