Research on the Method of Multi-Agent and Multi-Slug Combined to Achieve the Reservoir Equilibrium Displacement

Abstract

Summary The reservoir and fluid properties determine that a single injected fluid will inevitably undergo channeling during displacement. Whether it is water flooding, gas flooding, or steam flooding, it is necessary to control the injection-production profile. This paper aims to design the multi-agent and multi-slug combination displacement to achieve the equilibrium production of reservoirs. Considering the heterogeneity and median permeability of the reservoir, six three-parallel core models were designed. Polymers, hydrophobic association polymers, microspheres, and PPG are multi-agent profile control systems. The displacement equilibrium factor (DEF) was established by comprehensively considering the profile improvement, oil increase, and oil recovery. The optimal switching time can be determined according to the relationship between DEF and the variation coefficient of oil recovery of each layer. Finally, the five-parallel cores displacement experiments were used to verify the EOR effect under the guidance of DEF. Three-parallel core flooding experiments show that the best EOR efficiency can be obtained by plugging from the high permeability layer to the low permeability layer based on fully producing high-permeability layers. Water flooding - associated polymer flooding - microsphere flooding can increase oil recovery by 25.8% after water flooding. Calculate the DEF of 24 single-slug displacements, and draw a scatter diagram with the variation coefficient of the three layers’ oil recovery. The chart has an obvious inflection point that when the DEF is lower than 45%, the difference in the oil displacement effect is enhanced. Therefore, DEF reduced to 45% is the best time to switch the injection slug. The five-parallel core flooding experiments with the DEF<45% as the switching guidance can increase the oil recovery by 17.79% based on association polymer flooding, which is 9.68% higher than that of the conventional profile control method. Slugs combination mode and switching time of each slug are critical problems in applying multi-agent and multi-slug combination displacement. This work forms a combination idea of prioritizing the full use of high-permeability layers and then plugging them step by step. Meanwhile, a method of using DEF to dynamically guide the switching timing of each slug is formed. This paper can provide theoretical and experimental support for the optimal design of polymer injection parameters in oilfields.