Study on Matching Relation Between Polymer Molecular Size and Pore Size for Conglomerate Reservoir

Abstract The matching relation between the molecular size of polymers and the pore size of Karamay conglomerate reservoir in Xinjiang oil field was studied. By employing the nuclepore film filtration method, core flooding experiments and dynamic light scattering method (DLS), the molecular size of several candidate polymers for the pilot test was examined. And several suitable polymers for different reservoirs permeability were obtained. In the microporous membrane filtration experiments, the polymer DQ3500 with the molecular weight of 3.57 × 107 matched the 0.7 mm microporous membrane well. Moreover, three polymer samples including DQ2500 (molecular weight 2.42 × 107), complex polymer BCF (molecular weight 2.42 × 107) and complex polymer ABCF (molecular weight 2.14 × 107) matched the 0.6–0.7 mm microporous membrane well. No retained aggregation was observed on the microporous membranes for all examined polymer samples. Both resistance coefficient (Fr) and residual resistance coefficient (Frr) were measured with five core polymer flooding experiments. Polymer solution including DQ3500 and DQ2500 with the concentration of 1000 mg / L were injected into the artificial cement conglomerate cores with permeability of 121 × 10-3-1000 × 10-3 µm2. The values of Fr and Frr increased with the increasing of polymer molecular weight and decreased with the increasing of core permeability. The average polymer coil hydrodynamic radius (Rh) was measured by the DLS method. The Rh ranged from 266.0 nm to 394.5 nm for the polymers with molecular weight from 2.14 × 107 to 3.57 × 107. Accordingly, the conglomerate reservoir with water permeability more than 55.4 × 10-3 µm2 could not been blocked by those polymers with molecular weight less than 3.57 × 107.