Circular RNAs (circRNAs) are stable covalently closed non-coding RNAs (ncRNAs). Many studies indicate that circRNAs are involved in the pathological and physiological processes of liver cancer. However, the functions of circRNAs in liver cancer immunity are less known. In this review, we summarized the functions of circRNAs in liver cancer, including proliferative, metastasis and apoptosis, liver cancer stemness, cell cycle, immune evasion, glycolysis, angiogenesis, drug resistance/sensitizer, and senescence. Immune escape is considered to be one of the hallmarks of cancer development, and circRNA participates in the immune escape of liver cancer cells by regulating natural killer (NK) cell function. CircRNAs may provide new ideas for immunotherapy in liver cancer.
Most experimental results demonstrate that the first normal stress difference of viscoelastic polymer solution is higher than the second normal stress difference. Therefore, the Upper-Convected Maxwell (UCM) equation is adapted to describe this property. The steady flow mathematical model of UCM fluids is established. The simulation results of the Finite Volume Method are given. The Finite Volume Method can effectively ensure the convergence together with improvement in the calculation accuracy. The Weissenberg number (We) of the Finite Volume Method can be calculated to 3.2, which is higher than by the Finite Differential Method to simulate the flow characteristics of polymer solutions. When using the Finite Differential Method, the Weissenberg number can only be less than 0.4, otherwise it cannot converge. The contours of stream function and velocity of polymer solution with different Weissenberg number (We) or Reynolds number (Re) are drawn in three simplified micro-pore structures, expansion channel, contraction channel and expansion-contraction channel, respectively. The influence of Weissenberg number (We) and Reynolds number (Re) on microscopic sweep efficiency is studied. Numerical results show that the viscoelasticy of polymer is the main property that increases the sweep efficiency. With the increase in elasticity, the solution velocity of micro-pores at the corner of where the diameter suddenly changes is bigger; the flow region is enlarged, which is favorable for the residual oil becoming moveable, thereby increasing the micro-scale sweep efficiency. The higher the Reynolds number (Re) is, the larger the micro-scale sweep efficiency will be. But in reservoir condition, Reynolds number (Re) has little influence on improving the micro-scale sweep efficiency. The above results are important to further understand the mechanism of driving fluid viscoelasticity increasing the Displacement Efficiency of porous medium.
In the process of the tight oilfields development, it is difficult to establish an effective system of injection-production displacement because of the high seepage resistance. The seepage does not follow the linear Darcy's law. However, the reservoir simulation software has not considered this phenomenon, which leads to the numerical simulation prediction results better than actual production data. Therefore, it is necessary to establish an effective method to calculate the low velocity non-Darcy flow in tight sandstone oil reservoirs numerical simulation. This paper introduced a factor called starting pressure gradient (SPG), which can be used to describe non-Darcy seepage phenomenon. First of all, laboratory experiments of differential pressure flow method were carried out to get the relationship between core permeability and the SPG. In addition, according to the reservoir heterogeneity and exploitation degree, three methods were put forward for characterization the SPG in tight sandstone oil reservoirs numerical simulation. Finally, this numerical simulation method was used in the X tight sandstone oil reservoir history matching process to verify its accuracy. The results of the laboratory experiments showed that, SPG exists in tight sandstone oil reservoirs. Liquid starts to flow when the production pressure gradient is greater than the SPG. SPG is an additional pressure resistance for each flow unit, the existence of SPG has intensified the degree of pressure drop. Analysis of the experimental data gave a power series relationship between the SPG and the permeability. And the SPG increases with the decreases of core permeability. Reservoir heterogeneity criterion was established by introducing R and C factors. The greater R value and C values are, the higher the heterogeneity is. When the reservoir heterogeneity is weak (0< R≤0.3), we set SPG for each layer. When the reservoir heterogeneity is strong (0.3 < R≤ 1 or 0 < C≤1), we set SPG for each rock type. When the reservoir with intense heterogeneity (1<C<2), we set SPG for each gird. After considering SPG, single well history matching coincidence rate improves from 64% to 87%, and every layer oil production prediction has high coincidence with the actual production data. Therefore, SPG cannot be ignored in tight sandstone oil reservoirs numerical simulation. This paper provides a new method to describe the low velocity non-Darcy flow in tight sandstone oil reservoirs numerical simulation, and can guide the tight sandstone oil reservoirs development effectively. This method can also be applied in heavy oil reservoirs and tight gas reservoirs numerical simulation.
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