Evaluation of sweep efficiency in flooding process of reservoir development using substitution index

On the basis of a mathematically proposed concept, substitution index (SI), a practical method has been successfully applied to accurately evaluate the sweep efficiency during the development of reservoirs (e.g., waterflooding or polymer flooding). More specifically, the region that is swept by the injected water or the degree of sweeping in a specific region can be quantitively determined by means of the concept SI. As such, SI is considered to not only reflect the exchange degree in the pore between the injected water and initial oil from the microscopic view, but also describe the sweep performance of the whole field from the macroscopic view. Furthermore, a low-permeability reservoir (1.8 mD), which grows abundant high permeability channels and the large throats, is introduced as the case study to validate the proposed evaluation method for sweep efficiency in the process of its development. Waterflooding is firstly applied to recover oil in this field, and then profile control technique by injecting polymer-microsphere is implemented. Finally, it is found that the sweep efficiency increases from 0.282 to 0.311 before and after the polymer-microsphere injection.