Carbon Nanofiber-Enhanced HPAM/PEI Gels for Conformance Control in Petroleum Reservoirs with High Temperatures

Nanoparticles have recently been widely used in polymer gel systems to enhance gel strength. However, it is yet unclear how various types of nanoparticles affect the gelation characteristics of polymer gels. In addition, nanomaterials are rarely studied for enhancing the temperature resistance of polyethyleneimine (PEI) cross-linked polyacrylamide gels (i.e., HPAM/PEI gels). Under the urgent requirements of global carbon neutrality, this paper intends to use carbon nanofibers as gel performance-enhancing materials. Furthermore, the mechanism of their influence on the gelation properties and temperature resistance of HPAM/PEI gels was investigated. We evaluated the gelation time of the carbon nanofiber-enhanced HPAM/PEI gels at both 80 and 150 °C by the Sydansk method. The gelation properties and microscopic network structure of the gels were evaluated by rheometer, differential calorimetry scanning/thermogravimetry, and scanning electron microscopy. Results show that adding carbon nanofibers could delay the gelation time at 80 °C, and the gelation time of the polymer gel system reaching F was more than 6 days. On the other hand, the addition of carbon nanofibers could slightly shorten the gelation time of the polymer gel at an ultrahigh temperature of 150 °C. Moreover, the gel strength reached the highest when the addition amount of carbon nanofibers was 0.1%. The gel strength (G′) was as high as 12 Pa, and its stability was as long as 30 days, which was more temperature-resistant than that without adding nanofibers. The microstructure of carbon nanofiber-enhanced HPAM/PEI gels showed many tiny pore-like structures, which might be more conducive to heat dissipation and prevent dehydration. As a result, the carbon nanofiber-enhanced HPAM/PEI gel system had outstanding thermal stability and could be applied in ultrahigh-temperature reservoir conditions while maintaining high plugging strength. This study can present new ideas for improving the nanoparticle-enhanced HPAM/PEI gels in high-temperature petroleum reservoirs and further improving oil recovery, which has essential reference significance.