Effect of stress relaxation and creep recovery on transportation in porous medium and fracture of the millimeter-scale polymer gel particles for conformance control of heterogeneous oil reservoir

Abstract

To further improve the utilization of millimeter-scale polymer gel particles (PPGs) in the heterogeneous oil reservoir, it is necessary to investigate its mechanical state of transportation in porous medium and fracture. In this paper, for comparison, a non-uniform capillary and a uniform capillary are used to simply simulate the porous medium and the fracture, which is mainly applied to reveal the mechanical behavior of a PPG during transportation. Subsequently, the displacement experiments were carried out by using the heterogeneous core and the fractured cores, which is mainly applied to evaluate the influence of pore structure of the actual reservoir on the flow resistance of the PPGs and reveal the mechanical mechanism. The experiment result shows that the flow resistance in the uniform capillary of a PPG is less than that in the non-uniform capillary under the same conditions. This is because the transportation in the uniform capillary of a PPG is a process of creep recovery but the transportation in the non-uniform capillary of a PPG is a process of stress relaxation. In the actual reservoir, the transportation in the porous medium of the PPGs is a continuous process of creep recovery, but the transportation in the fracture of the PPGs is a process of stress relaxation. During transportation, the flow resistance of PPGs in the porous medium is high, but the flow resistance of PPGs in the fracture is low. However, when the PPGs transport to the end of the partially open fracture, the PPGs fill the space of the partially open fracture, which can decrease the effective size of the partially open fracture and lead to the increase of the injection pressure. Therefore, the PPGs have a better plugging effect in the porous medium and partially open fracture but have a poor plugging effect in the open fracture. For the high-water-cut oil production well with the open fracture, it is not the best choice to directly use the PPGs as the plugging agent. The conclusions can provide a theoretical guidance for the highly efficient application of gel particles for conformance control in the heterogeneous reservoir.