Long-chain polyoxyethylene ether-modified nanomaterials and their oil recovery mechanism for low-permeability reservoirs

To address the challenges posed by tight reservoirs with low porosity, low permeability, and poor spontaneous imbibition, a novel nanofluid for enhanced oil recovery was developed. The nanofluid was formulated using laboratory-synthesized silica nanoparticles that were hydrophobically modified with a long-chain polyoxyethylene ether to obtain hydrophobically modified silica nanoparticles (PSNPs). The PSNPs were dispersed in de-ionized water with sodium dodecyl sulfate to formulate the nanofluid (PSNF). Due to its ultrafine particle size relative to conventional oil displacement agents, PSNF can effectively penetrate nanoscale pore throats and promote displacement efficiency. PSNF enables fast migration to the oil–water–solid interfaces and effectively promotes oil film detachment from rock surfaces. The nanofluid achieves an interfacial tension reaching the order of 10−3 mN/m against crude oil and reduces the contact angle from 95° to 20.4°, indicating excellent interfacial activity and effective wettability alteration. At a concentration of 0.3%, the nanofluid exhibits a spontaneous imbibition height of 24 mm and an imbibition efficiency of 31.48%. The superior imbibition performance of the PSNF nanofluid was further corroborated by nuclear magnetic resonance core analysis. These results demonstrate the strong potential of PSNF for enhancing oil recovery in low-permeability tight reservoirs.