Mobility Control through Polymer-Gas Cycling in Daqing X Block: Injection Design and Recovery Tradeoffs

doi: 10.14800/sp.1316

Abstract

Polymer-alternating-gas (PAG) injection seeks to combine the microscopic displacement efficiency of gas with the mobility control of a viscous polymer solution. A three-dimensional CMG-GEM model of the Daqing X Block was used to optimize PAG operating variables and compare PAG with water flooding, polymer flooding, and water-alternating-gas (WAG). Sensitivity screening was followed by an L16 orthogonal design covering polymer concentration, polymer slug volume, gas-to-water cycle ratio, number of cycles, and the water-cut threshold for switching to PAG. The model uses common operational constraints, including a 30 MPa maximum injector bottom-hole pressure, 5 MPa minimum producer pressure, 85 m3/d liquid injection, and 115 m3/d liquid production. The results show that PAG delays unfavorable gas mobility, improves volumetric sweep, and raises cumulative recovery relative to the alternative cases. Performance is controlled by the balance between polymer mobility reduction and gas contact efficiency rather than by maximizing polymer dosage. The optimized scheme provides a field-oriented basis for selecting polymer concentration and alternating schedule in a heterogeneous mature reservoir.