High Efficient Deep Fluid Diversion Technique And Its Mechanism Analysis

Major domestic oil reservoir was of serious heterogeneity, which was more and more aggravated owing to long-term water flooding. At present, many oil fields in the east entered high or ultra-high water cut stage. The waterflooding effect was unfavorable due to the low or invalid circulation of injected water in the high permeable zones. Therefore, there was an urgent need to carry out fluid diversion measure to enlarge the swept volume and improve the flooding effect. For the needs of oilfields, a great deal of research was conducted on necessity of fluid diversion technique, composition and performance of displacing agent, selection and properties of fluid diversion agent, types of fluid diversion agent and its compatibility with the reservoir rocks, combination of displacing agent and fluid diversion agent and increamental oil effect, and EOR mechanism of fluid diversion. The results showed that, when reservoir is of serious heterogeneity (VK>0.72), compared with displacement efficiency, fluid diversion (swept volume enlargement) palyed an important role in enhancing oil recovery. Generally speaking, selection of fluid diversion agents and its slug combination was mainly depending on average permeability and heterogeneity of reservoir. So, particles were suitable for the reservoir with large pore or ultra-high permeable layer. "Particles+polymer gel" combination had much better effect on fluid diversion. In addition, polymer gel was suitable for low and middle permeability reservoir, especially for the polymer gel with intra-molecule cross-linking structure, who was of a better performances on fluid diversion. Moreover, the earlier the injection time and the larger the injected volume, the better the diversion effect and increment of recovery efficiency. The remaining oil distribution was mainly influenced by reservoir heterogeneity, well spacing, types, and injected volume of fluid diversion agent. The remaining oil distributed in the middle and low permeability zone far away from the injection well vertically, and distributed in both sides far away from the mainstream line horizontally. The slug combination of "fluid diversion agent+displacing agent", which can improve the displacement efficiency and sweep efficiency at low cost, had good effect on enhancing oil recovery. With the fluid diversion agent injiected and absorbed in large pores or high permeability layers, flow resistance and injiection pressure increased, which led to increase in imbibition pressure and imbibition volume of middle and low permeability layers. The presure gradient and driving force increased due to the increase in injection pressure, which resulted in the increase of sweep efficiency microscopically. The relative permeability of water phase was much lower after the fluid diversion flooding than that of after water flooding.