Synergistic Mechanism of Water-Alternating-Gas Injection and Elastic Microsphere Plugging for Gas Channeling Control in Immiscible Gas Flooding: Experimental Insights from the Weizhou 12-1 Oilfield.

During gas displacement in low-permeability reservoirs, technologies such as gas-water alternation and foam blocking have partially mitigated gas displacement issues. However, the complexity of gas displacement pathways and variations in the advancement speed of the displacement front often lead to "finger-like" or bypass phenomena. These effects result in poor gas-displacement uniformity, low gas-displacement efficiency, reduced oil recovery efficiency, irreversible reservoir damage, and high-temperature material failure. To address the challenges of high-temperature (125 °C), low-permeability (40 × 10-3μm2) reservoirs with poor gas flow and low oil-recovery efficiency during gas injection in the Weizhou 12-1 oilfield,this study proposes a composite plugging system based on is mechanism synergistically optimized the mobility ratio with WAG, redirected fluids toward low-permeability zones, and significantly reduced gas channeling, resulting in a 59.94% increase in oil recovery efficiency compared to a single WAG.(2) Development of 170 °C high-temhigh-temperature-resistant polymer microspheres for water-alternating gas (WAG) injection. The minimum mixed-phase pressure (36.16 MPa), determined through fine-tube experiments, revealed the limitations of nonmixed-phase rejection under the current gas injection pressure (17 MPa). Three key breakthroughs of the composite system were validated:(1) First synergistic mechanism of "mobility control + deep blocking": Microspheres (4000 mg/L) achieved a 99% blocking rate via elastic deformation and deep bridging. Thperature-stabilized microspheres:These microspheres surpassed the conventional thermal limit (<120 °C) and demonstrated a residual resistance coefficient of 4.28.(3) Proposed dynamic intervention timing:A gas-liquid ratio of 500 (early stage of gas channeling) yielded a 6.84% improvement in injection efficiency compared to a gas-liquid ratio of 1100. This composite system provides an efficient, low-cost solution for controlling gas channeling in high-temperature heterogeneous reservoirs in the South China Sea.