Study On Multi-slug And Equi-fluidity Displacement After Water Flooding

Chemical flooding is one of the most important methods to enhance oil recovery when the main oil fields in our country have been in the stage of high water cut at present. However, because of the heterogeneity of formation and other factors, chemical flooding has the problems of single injected agent, high injection, as well as that the low permeability layer can't be flooded and so on, and there are still a lot of residual oil that have not been developed in formation. In order to further enhance the oil recovery after water flooding, the multi-slug and equal mobility flooding method which the high, medium and low permeability layers can be flooded simultaneously is developed in this paper according to the properties of the present high water cut and the heterogeneity of formation, and the flooding mechanism of the method is dicussed. Meanwhile the slugs are designed and the experimental formulas to determine the length and volume of every slug are also established.The affections of NaCl, MgCl₂ and CaCl₂ with different concentrations on the viscosity of different types of function polymer and HPAM solution are studied through the selection and evaluation of the agents used for multi-slug and equal mobility flooding. It is indicated that the function polymer has good salt tolerance ability; The foaming capacity of several types of surfactant and typeâ…¡function polymer are evaluated by using the Waring Blender method, and finally HY-2 is selected to be the foaming agent in experiment, meanwhile the typeâ…¡function polymer also shows good foaming capacity. Alkanolamide was selected as the surfactant used for displacing oil by measuring the interfacial tension, and the interfacial tension can reach 4.1×10^-3mN / m when the concentration is 0.6%.The flooding effects of multi-slug and equal mobility method after water flooding have been studied through indoor physical simulation experiment. The concept of gathered energy strength is introduced to analysis the experimental results. It can be indicated from the experiment that the multi-slug and equal mobility method can control the water cut effectively and increase the gathered energy strength substantially. After water flooding the recovery can be increased by 40%, and finally the total recovery is developed to over 80% which is significantly higher than that of currently used polymer flooding and ASP. Meanwhile comparing with ASP, the economic benefit of multi-slug and equal mobility flooding is very remarkable, which is 2.3 times of the economic benefit of ASP.