Study On Polymer Crossflow Law

Polymer flooding has been an important enhanced oil recovery method adopted at the later stage of oilfield development in China. However, due to the long-term water flooding, great changes have happened to the formation and the fluid. Although the water shut-off and profile control have been implemented before, in the polymer flooding the crossflow is readily formed along the dominant flow field, which leads to the earlier polymer production in producers, the faster increase of water cut, the diminishing sweep efficiency, and lower oil recovery. Therefore, it is crucial to research the crossflow law of polymer and to explain the factors resulting in the crossflow from the mechanism aspect.Through experiment, the paper systematically studies the crossflow law of polymer with various methods. It begins with the research of polymer rheology, studies the research of different factors affecting the rheology and the sensitivity of these factors on the viscosity of polymer. And then the relationship between the consistency coefficient, power law exponent, and temperature as well as concentration is analyzed. With the support vector machine, the factors are coupled and the apparent viscosity of polymer is predicted. Based on the research above, through the cycle injection experiment on single core and shear rheological experiment on the parallel tubes, the rheological law of polymer is modeled under the formation conditions. And the researches about the effect of polymer concentration of polymer and its permeability on the shear viscosity are carried out. The reason why the crossflow of polymer happened in porous media is analyzed. This paper made different models to study the crossflow of polymer in various heterogeneity circumstances with visualization methods. The optimum polymer concentration is determined through comparing the relationship between the polymer concentration and the oil recovery under different heterogeneity on parallel tube experiments, which can provides the guidance for the optimization of polymer parameters. With the nuclear magnetic resonance technology, the paper researches the distribution of crossflow of polymer in porous media under different processes and various heterogeneity conditions. The effect of pore structure on crossflow of polymer, and the distribution of fluid in porous media in different stage are analyzed. It is found that the re-allocation of crude oil happened during the crossflow. According to the characteristics of crossflow, this paper determined the range of pore diameter, after which the crossflow is occurred, and the distribution of remaining oil. With the CT nondestructive examination technology, the paper researches the distribution of polymer after crossflow from microscopic aspect. And the image is analyzed with image division method. It is shown that the crossflow is dependent on the microscopic structure of the pore. The slices in different positions indicate that the distribution of polymer after crossflow satisfies the Gauss distribution function. The crossflow of polymer is affected by the combination of rheology of polymer and heterogeneity of formation. The result can provide theoretical guidance and technological support for the prevention of crossflow in oilfield, and it is of great significance for the prevention of polymer crossflow.