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The molecular weight of polymer is important to the efficiency of polymer flooding. Polymer solutions with higher molecular weight have better absorption, better capitation, higher resistance and residual resistance coefficients. All these imply higher recovery factor. But for reserviors of middle and low permeability, higher injected molecular weight means more unswept pore volume, lower controlling degree and recovery factor. Therefore, both higher injected molecular weight and controlling degree must be fully considered, so as to obtain a higher recovery factor in a given block.On the basis of lab experiments and numerical simulations, two matching charts are formed. One is about the relationship between molecular weight and layers and the other is about controlling degree on recovery rate. They are used to optimize the molecular weight for polymer flooding. This new method is applied in the project for polymer flooding in secondary layers of Daqing oilfield and an enhanced recovery factor of more than 8% is obtained.

The sandwich structures are three- or multilayered structures such that their mechanical properties are better than each single layer. In the current research, a three-layered cylindrical shell including a functionally graded porous core and two reinforced nanocomposite face sheets resting on the Pasternak foundation is used as model to provide a comprehensive understanding of vibrational behavior of such structures. The core is made of limestone, while the epoxy is utilized as the top and bottom layers’ matrix phase and also it is reinforced by the graphene nanoplatelets (GNPs). The pattern of the GNPs dispersion and the pores distribution play a crucial role at the continuous change of the layers’ properties. The sinusoidal shear deformation shells theory and the Hamilton’s principle are employed to derive the equations of motion for the mentioned cylindrical sandwich shell. Ultimately, the impacts of the model’s geometry, foundation moduli, mode number, and deviatory radius on the vibrational behavior are investigated and discussed. It is revealed that the natural frequency and rotation angle of the sandwich shell are directly related. Moreover, mid-radius to thickness ratio enhancement results in the natural frequency reduction. The results of this study can be helpful for the future investigations in such a broad context. Furthermore, for the pipe factories current study can be effective at their designing procedure.

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