An efficient degradation method for reservoir damage gel-like substances after hydraulic fracturing

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This study systematically investigated the gel-like blockage problem in unconventional oil and gas reservoirs in the Sichuan Basin after hydraulic fracturing. Field gel samples were characterized by X-ray diffraction analysis and infrared spectroscopy analysis, confirming that the main component was a cross-linked product formed by the reaction of polyacrylamide drag reducers with trivalent metal ions dissolved in the formation. Experimental simulations revealed that divalent metal ions (such as Ca2+) did not cause gelation, while iron ions were the key factor. Regarding degradation methods, traditional peroxide gel breakers (such as ammonium persulfate) were ineffective when used alone, but citric acid through chelation to displace metal ions and ammonium persulfate through free radical cleavage of polymer chains, working in synergy, could achieve efficient degradation. The optimized solution indicated that a mixture of 5% citric acid and 1% ammonium persulfate could completely degrade 10 g of gel at 90 min (67 °C), and performed better than single reagents at different temperatures (40 °C–67 °C). This research not only clarified the gel formation mechanism but also proposed an efficient degradation strategy, which is of significant engineering importance for restoring reservoir permeability, enhancing oil and gas production, and reducing environmental damage.