Application of High-Strength, High-Temperature-Resistant, and Degradable Inorganic Gel for Preferential Flow Path Plugging in Cyclic Steam Stimulation of Bohai N Extra-Heavy Oil Reservoir

The Bohai N extra-heavy oil reservoir suffers from severe inter-well steam channeling, high water cut, and high water recovery rate during cyclic steam stimulation (CSS), which is primarily caused by preferential flow paths formed by interchannel microfacies (low-quality reservoirs with permeability of 200–500 mD and water saturation of 40–70%). Conventional nitrogen foam cannot effectively plug such channels due to its insufficient mechanical strength and long-term stability. In this study, a high-strength, high-temperature-resistant, and degradable inorganic gel (HSHTR-IG) was developed. Its optimal formula is determined as 20 wt % polysulfonated magnesium aluminum silicate (main agent), 3 wt % polyamide (cross-linker), 1 wt % stabilizer, and 1 wt % high-temperature corrosion inhibitor. Laboratory tests show that the system has a thermal decomposition temperature of 380 °C; after aging at 350 °C for 30 days, its breakthrough pressure reaches 3.96 MPa, and the plugging efficiency exceeds 97.5%. CMG STARS simulations predict that HSHTR-IG can divert steam into high-quality pay zones, increasing the steam sweep efficiency from 42% to 68%. Field application in Well A15H increased the daily oil production from 30 m3 to 63 m3, reduced the water cut from 75% to 54%, and achieved an input–output ratio of 6.29 at an oil price of $50 per barrel. This work provides a reliable enhanced oil recovery (EOR) technique for offshore extra-heavy oil reservoirs with well-developed preferential flow paths.