A unique preformed particle gel with re-crosslinkable ability to reform bulk gel for chemical enhanced oil recovery of void space conduits containing reservoir is described herein. The formation of the bulk gel was achieved by reversible ionic crosslinks of the preformed particle gels as induced by brine under reservoir conditions. The re-crosslinked hydrogel with ionic features showed rubber-like mechanical behaviors, a critical parameter of the particle gels to increase plugging efficiency. The re-crosslinking ability of the preformed particle gels under different salinity could be controlled by tuning the ionic interactions within the hydrogel. In addition, the long-term thermal stability of the re-crosslinked bulk gel has been demonstrated. Furthermore, the re-crosslinked bulk gels could significantly reduce permeability of large fractures as demonstrated by core flooding experiments compared with traditional preformed particle gels. The re-crosslinkable bulk gel with robust mechanical properties could offer the candidate to block void space conduits containing reservoirs for enhanced oil recovery.
A robust starch-grafted nanocomposite preformed particle gel (SN-PPG) with superior viscoelasticity and thermal stability is developed to improve the oil recovery. The effects of a cross-linker, an initiator, starch, sodium montmorillonite (Na-MMT), and additives thereof were systematically studied. Through introducing starch and Na-MMT, the storage modulus of the swollen gel was ameliorated from 570 to 1420 Pa. At 80 °C, the SN-PPG exhibited thermal stability after aging for 90 days; meanwhile, it showed an inflection temperature of 187.3 °C in the differential scanning calorimetry measurements, which indicated excellent thermostability. Moreover, the SN-PPG displayed a reinforced pH and salinity tolerance compared with the conventional PPG. In core-flooding tests, the SN-PPG successfully blocked the fracture aperture and improved the oil recovery by 29.86−38.59%. Furthermore, the characterizations involving Fourier transform infrared spectroscopy and scanning electron microscopy confirmed the decoration mechanism of starch grafting and Na-MMT nanocompositing. The results showed that the robust SN-PPG could be a candidate for remedying the conformance problem and improving the oil recovery for high-temperature and high-salinity reservoirs.
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