Facile synthesis of temperature-resistant hydroxylated carbon black/polyacrylamide nanocomposite gel based on chemical crosslinking and its application in oilfield

Abstract With the continuous extraction and consumption of light oil resources, heavy oil is of growingly importance for industrial development. However, conventional displacement methods are not suitable for heavy oil due to its high viscosity, resulting in low oil recovery. Steam flooding is one of the most effective means to exploit heavy oil reservoir, and the injection profile greatly influences its oil production. As the most powerful plugging agent, the high temperature steam (200 °C) and complex mechanical environment in formation require gel to have good temperature resistance and shear resistance for profile control. In this work, we synthesized a HCB (hydroxylated nano carbon black) by grafting hyperbranched polyester onto its surface, and crosslinked it with polyacrylamide (PAM) by chemical reaction to prepare a high-strength temperature-resistant hydrogel HCB/PAM for profile control. In contrast to the conventional reinforcing filler (such as SiO2 and ordinary carbon black nanoparticles) physically crosslinked in gel, HCB can be uniformly dispersed in PAM gel through covalent bond connection between its surface terminal hydroxyl groups and PAM amide groups, and form a chemical crosslinking composite gel composed of carbon material and polymer. As such, the strong chemical bonding can effectively improve temperature resistance, mechanical properties and water retention capacity of HCB/PAM gel. On the other hand, compared with the highly crosslinked PAHHP (Polyacrylamide-hexamethylenetetramine-hydroquinone-polyethyleneimine) gel previously reported, HCB/PAM-0.5 gel (the optimal sample), being of good profile control ability, can effectually mitigate formation damage caused by steam flooding. Core flooding experiments showed that in comparison with PAHHP, the HCB/PAM-0.5 had larger plugging intensity and scope due to its robust 3D network and soft nature, leading to higher oil production. Meanwhile, without crosslinking agent, core permeability and porosity were decreasingly impacted by HCB/PAM-0.5. Generally, HCB/PAM-0.5 gel has better profile control ability and lower formation damage. These findings of this study can help better understand the relationship of gel flexibility and strength, thus offering references for enhancing oil recovery and handling formation damage.