Abstract
Polymer injectivity is an important factor for evaluating the project economics of chemical flood, which is highly related to the polymer viscosity. Because the flow rate varies rapidly near injectors and significantly changes the polymer viscosity due to the non-Newtonian rheological behavior, the polymer viscosity near the wellbore is difficult to estimate accurately with the practical gridblock size in reservoir simulation. To reduce the impact of polymer rheology upon chemical EOR simulations, we used an efficient multilevel local grid refinement (LGR) method that provides a higher resolution of the flows in the near-wellbore region. An efficient numerical scheme was proposed to accurately solve the pressure equation and concentration equations on the multilevel grid for both homogeneous and heterogeneous reservoir cases. The block list and connections of the multilevel grid are generated via an efficient and extensible algorithm. Field case simulation results indicate that the proposed LGR is consistent with the analytical injectivity model and achieves the closest results to the full grid refinement, which considerably improves the accuracy of solutions compared with the original grid. In addition, the method was validated by comparing it with the LGR module of CMG_STARS. Besides polymer injectivity calculations, the LGR method is applicable for other problems in need of near-wellbore treatment, such as fractures near wells.
Highlights
Polymer flooding has become one of the most widely used enhanced oil recovery (EOR) methods because of its adaptability to a wide range of oil viscosity (Wassmuth et al 2007), relative simplicity for operations (Mohammadi and Jerauld 2012), and offshore applicability (Morel et al 2012)
Polymer injectivity is an important factor for evaluating the project economics of chemical flood, which is highly related to the polymer viscosity
To reduce the impact of polymer rheology upon chemical EOR simulations, we used an efficient multilevel local grid refinement (LGR) method that provides a higher resolution of the flows in the near-wellbore region
Summary
Polymer flooding has become one of the most widely used enhanced oil recovery (EOR) methods because of its adaptability to a wide range of oil viscosity (Wassmuth et al 2007), relative simplicity for operations (Mohammadi and Jerauld 2012), and offshore applicability (Morel et al 2012). Sharma et al (2011) proposed to use an effective well radius to calculate the shear rate and match the polymer injectivity from very fine-grid simulation results; Li and Delshad (2014) proposed an effective viscosity using mathematical integration of in situ viscosity by assuming a radial velocity distribution within the well block. These approaches are not rigorous for other near-well effects apart from polymer rheology, e.g., non-zero skin factor, polymer permeability reduction, and injection induced fractures near the wellbore, which are often encountered during injection of polymer solutions. The LGR simulations are compared to those using the analytical injectivity model proposed by Li and Delshad (2014)
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