Synthesis and evaluation of magnetite nanoparticles coated with (acrylamide-vinylpyrrolidone) polymers on the thermostability for application in harsh offshore reservoirs

Abstract

To avoid the instability and degradation of downhole injection fluids, such as polymers and surfactants, for use in high-temperature (HT) offshore reservoirs, nanofluids with particles modified in different ways have been proposed as a capable thermoresistant, highly active solutions which can be used in many offshore oil and gas exploitation works, especially in enhancing oil recovery. This study presented the process of synthesising two nanocomposite materials for nanofluid preparation. First, magnetite nanoparticles (MNPs(A and B)) were prepared by standard coprecipitation and hydrothermal methods. Then, polymer-coated magnetite nanoparticles (PCM(A) and PCM(B)) were synthesised by directly covering magnetite with oleic acid (OA) to get OA-MNPs, and then simultaneously enveloped with copolymers of acrylamide and the N-vinyl pyrrolidone via polymerisation reaction. The obtained PCMs characteristics were analysed by all required analytical tools. In addition, the thermostability of PCM-based nanofluids as downhole injection agents for HT offshore reservoir applications was investigated by bottle test annealing PCM(A)- and PCM(B)- based nanofluids at the White Tiger (WT) Miocene and Oligocene reservoir temperatures. Based on the obtained data, MNPs have an average particle size of 12 nm and 10 nm for MNPs A and B. A dominant phase of magnetite (Fe3O4) and 10.5% and 11% of the mass of PCM belong to their copolymer coating. The good thermostability of nanofluids annealed for 31 days (at 120 °C for PCM(A)- and 134 °C for PCM(B)-based nanofluids) showed a promised orientation for use as an EOR agent in HT offshore reservoirs recommendation.