Quantitative Characterization of Dynamic Heterogeneity in Reservoirs With Stratified Noncommunicating Layers

Due to the difference of permeability in reservoir and viscosities between oil and water, oil displacement efficiencies at different locations differ significantly. Also, along with the water flooding process, the differences of oil displacement efficiencies change in time and manifest dynamic characteristics, which is called dynamic heterogeneity in this paper. A new parameter called “conductivity index” (I_C) is defined, and the Gini coefficient of I_C (GC_IC) is selected to quantitatively characterize the dynamic heterogeneity in reservoirs with stratified noncommunicating layers. Then, the changing laws and influential factors of GC_IC are investigated by physical experiments and numerical simulation methods. Finally, the application of dynamic heterogeneity in individual-layer water injection technique is studied. Based on the theory of seepage flow mechanics, the formula of I_C is derived. I_C not only contains static parameters including permeability, water, and oil viscosity but also contains dynamic parameters including water and oil relative permeabilities, which are both function of water saturation and also function of rock type. Therefore, I_C can reflect the dynamic heterogeneity caused by water flooding process. A five parallel sandpacks' water flooding experiment is conducted to investigate the changes of dynamic heterogeneity. Results show that the value of GC_IC increases rapidly before the water breakthrough of the sandpack with highest permeability. Then, after water breakthrough, GC_IC decreases slowly. A new parameter GC_I is defined to represent the average increase of GC_IC during the water flooding process. By numerical simulation method, the influences of Gini coefficient of permeability (GC_P) and oil viscosity on GC_I are studied. Results show that GC_I increases along with the increase of oil viscosity. And GC_I first increases and then decreases along with the increase of GC_P. When GC_P equals 0.6, GC_I gets its maximum value. Taking block P of Shengli Oilfield in China, for example, the changes of dynamic heterogeneity along the water flooding process are studied. Results show that the dynamic heterogeneity of each well group varies greatly before and after water flooding. For some well groups, the relative sizes of GC_IC even reverse. The performances of different cases in individual-layer water injection technique are investigated by numerical simulation method. Results show that the case both considering dynamic heterogeneity and the remaining oil volume gets the best performance.