Influences of Fracture Aperture on the Water-Shutoff Performance of Polyethyleneimine Cross-Linking Partially Hydrolyzed Polyacrylamide Gels in Hydraulic Fractured Reservoirs

In previous study, we have discussed the gelation performance of the polyethyleneimine (PEI) cross-linking partially hydrolyzed polyacrylamide (HPAM) gel system. The major goals of this paper are to investigate the conventional application performance of the PEI cross-linking HPAM gel system, including injectivity and sealing charactersic through core flowing experiments. Results show that polymer gels formualted with a combination of 2.0 wt % HPAM (M-w = 8000 kDa) and 0.35 wt % PEI can achieve the critical pressure gradient above 500 psi/ft on average and with a maximum at 1136.38 psi/ft through the core flowing experiments with apertures ranging from 0.080 to 0.200 cm. The pressure gradient and brine permeability reduction factors (F-rrw) are also attractive. The gradient pressure is inline with expectations of the gradient pressure predicting curve obtained by Seright for the chromium (III) acetate cross-linking HPAM gel. A strong adhesive force of stretching 2 cm width rather than breakage in fracture profile is observed after gel washout, showing that PEI/HPAM gels have strong and durable mechanical performance to withstand brine flowing. Atomic force microscope (AFM) scanning results exhibit that disorderly cavities are distributed in the microstructure of dehydrated gels, seem like a honeycomb. Free water existing in the gel network can be easily removed through these cavities for gel dehydrating. The evaluation of the basic application performance demonstrates that the PEI cross-linking HPAM gel is a promising sealing agent for use in fractured reservoirs.