Conventional polymeric systems face significant challenges in maintaining performance under high-temperature, high-salinity reservoir conditions due to limited thermal and saline stability. To address this critical limitation, a hydrophobically modified biopolymer (HWLG) was synthesized via etherification of Welan gum (WLG) with 1-bromooctadecane, introducing alkyl grafts to create hydrophobic microdomains. Comprehensive structural characterization was performed using Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance spectroscopy (NMR), gel permeation chromatography (GPC), thermogravimetry analysis (TGA), and scanning electron microscopy (SEM), confirming successful alkyl incorporation. Rheological evaluations demonstrated HWLG’s concentration-dependent pseudoplasticity, achieving a viscosity of 1423.2 mPa·s at 4000 mg·L⁻¹, which was about 3.4 times that of WLG at 70 ℃. The HWLG solution showed superior temperature and salt resistance in comparison with unmodified WLG, due to hydrophobic association-driven network formation. Particularly in formation water, HWLG showed a better long-term thermal stability, retaining 64.5% viscosity after aging 50 d at 70 ℃, compared to WLG’s 39.6% retention. Core flooding experiments validated HWLG’s EOR efficacy, delivering 22.6% incremental oil recovery versus WLG’s 13.7%, driven by enhanced mobility control. The integration of hydrophobic functionality endows HWLG with exceptional thermosaline stability, adsorption capacity, and viscoelasticity, positioning it as a robust candidate for high-temperature, high-salinity reservoir flooding applications.

Novel wet-phase modified expandable graphite (WMEG) particles were developed for in-depth profile control in carbonate reservoirs. The harsh environment of carbonate reservoirs (≥ 130 ℃, ≥ 22 × 10⁴ mg/L) brings significant challenges for existing profile control agents. WMEG particles were developed to address this problem. WMEG particles were synthesized via intercalation with ultrasound irradiation and chemical oxidation. The critical expansion temperature of WMEG particles is 130 ℃, and these particles can effectively expand 3–8 times under high temperature and high salinity water. The core flow experiments show that WMEG particles exhibit a good plugging capacity, profile control capacity, and a better-enhanced oil recovery (EOR) capacity in deep carbonate reservoirs. WMEG particles can be expanded in the formation and form larger particles that bridge the upper and lower end faces of the fracture. Then the high-permeability zones are effectively plugged, and the heterogeneity is improved, resulting in an obvious increase in oil recovery. This research provides a novel insight into future applications of profile control agents for in-depth profile control treatment in carbonate reservoirs.

A novel nanofluid of modified carbon black (MCB) nanoparticles was initially developed for enhanced oil recovery (EOR) in low permeability reservoirs. The MCB nanoparticles were obtained via a three-step reaction involving modification by oxidation, acyl chlorination, and activated grafting. MCB nanoparticles were spherically dispersed, with an average size of 72.3 nm. Compared with carbon black (CB) nanoparticles, dispersed MCB nanoparticles can effectively reduce the oil–water interfacial tension (IFT) to 10⁻² mN/m and change the surface wettability of sand particles. Based on the results of core flooding experiments, the MCB nanoparticles exhibited a better EOR capacity than surfactants and CB nanoparticles, and the final oil recovery was significantly increased by 27.27%. The core scanning test showed that the MCB nanoparticles could plug high permeability channels by adsorbing onto the surfaces of sand particles and forming larger aggregates that bridge across pores or throats, resulting in a higher swept volume. The synergistic effects of improved swept volume and oil displacement efficiency were the EOR mechanisms of the MCB nanoparticles. The studies indicate that these MCB nanoparticles have excellent potential for EOR in low permeability reservoirs.