During water-flooding, strips of high permeability, namely big channel, can be easily developed in the sandstone reservoir for the influence of petrophysical properties and fluid. Based on the theories of petrophysics, fluids flow in porous media, and reservoir engineering and so on, this paper presents a mathematical model to describe big channel in reservoir underlow velocity laminar flow conditions, and using this model we simulated the change of big channel with water-flooding process. According to the increase of big channel size with the time increase in different locations, we demonstrated the forming process, size distribution and distributing area of big channels. Correlated with field data and physics simulationdata, this model can describe the change of big channels in reservoirs very well during water-flooding. In the waterblocking and profile controlling processes, this model is very important to the optimal design of the intensity of profile control agent and the injected slug volume.
Water-flooding is a widely used method for field exploitation and secondary oil recovery in the world. The field production practice indicates that reservoir's heterogeneity isserious and is apt to produce sand during water flooding, because the permeability of sandstone reservoir is high, and the clay cement is unconsolidated, and viscosity ratio of oil and water is high. After a long time of high-speed water flooding, the reservoir's pore structure has been changed greatly, and the channeling is serious in high and extra high permeability strip(namely big channel), which is formed in reservoir. These stripsmake lots of injected water cyclically produced inefficientlyalong big channels, so that the utilization efficiency of theinjected water is lower, meanwhile the pore volume swept bywater is reduced, and the improvement of oil recovery and development benefit is seriously affected [1,2,3]. At present, a lot of matured oil fields are in the stage of high water-cut, utilization efficiency of injected water and development benefit is becoming lower.
All these effects have some relationship with the big channel's forming in the reservoir.Further investigation on the discernment of big channel has very important realistic meaning for these methods to improve water swept pore volume and oil recovery efficiency, such as tertiary oil recovery, water blocking, profile controlling, injection-production structure adjustment, etc. Many research works have been done in the identification of big channel such as forming influence factors, forming process and identification methods, etc. [1,2,3,4], but no research about radius change and distribution of macroscopic pore-throat has been documented.When designing water blocking and profile controlling scheme, many works such as the intensity of profile controlling agent, the size probability distribution and the distributed area of big channel (for <0.5cm, 0.5 ~1cm, >1cm) are based on the formation of big channel during the reservoir rock flooded by the injected water. In this article, we have established the relationship of pore radius with water producing rate, studied the forming regularity of big channel during water flooding, discussed the relationship of big channel's forming process and size distribution with water flooding time.
