Study On Emulsion Polymer Composite Flooding System In Mid-Low Permeability Reservoir

As an instant polymer system,W/O emulsion polymer can be combined with surfactant for oil displacement to form a two component composite flooding system.But compared with the traditional binary composite driving system,the binary system prepared from W/O emulsion polymer contains not only conventional components such as polymer and surfactant but also white oil component,while the surfactant as displacing agent can emulsify white oil to form oil in water emulsion by adsorption on the interface of white oil and water.Therefore,the composition of the two component flooding system using W/O emulsion polymer and surfactant is more complex and the seepage rule is more special.In this thesis,a systematic study on this kind of binary flooding system was carried out.The individual properties of polymer and emulsion and the synergistic effect of the composite system formed by them were studied through the experiments of rheology,stability,resistance coefficient and displacement efficiency.The results show that polymers can enhance the coalescence stability of emulsion by increasing the viscosity of the continuous phase in the emulsion polymer composite system,while the internal friction of the oil droplets and the continuous phase in the emulsion further improves the apparent viscosity of the system.The resistance factor of emulsion,polymer and emulsion polymer composite system in the core of 10×10^-3-100×10^-3μm² was studied by core flow experiment.The results showed that the low oil content O/W emulsion and low concentration polymer significantly reduced the mobility of the oil displacement system through synergistic effect.In the low concentration polymer solution（0.02%）,adding a small amount of oil phase into O/W type emulsion polymer composite system can obtain a resistance factor（15.19-27.72）similar to that of high concentration polymer solution（0.05%-0.1%）.By this way,the mobility control of the flooding system can be ensured while the blockage of the high concentration polymer system to the formation can be avoided effectively.The core flooding experiment shows that for the medium low permeability core with permeability of 40×10^-3-150×10^-3μm²,the enhanced oil recovery ratio of emulsion polymer composite system reaches 10.93%-12.34%,which is better than that of polymer/surfactant flooding system of the same concentration.Finally,based on the equivalent flow viscosity,the calculation method of injection pressure of composite system in medium low permeability reservoir is improved,and the calculation program is compiled by using programming language.The influence of formation permeability,reservoir thickness,injection volume,injection speed and injection mode on injection pressure of composite system is quantitatively studied.The results show that the formation permeability has a significant influence on the injection pressure.The composite system will enter the formation with permeability greater than 100×10^-3μm² in priority,and play the role of fluidity adjustment and control.The injection pressure of the system can be effectively reduced by using the multi-stage plug injection method.The injection pressure can be estimated by this method and the injection parameters can be optimized according to the basic performance of injection production equipment.