Hydrocarbon resources in low-permeability sandstones are very abundant and are extensively distributed. Low-permeability reservoirs show several unique characteristics, including lack of a defi nite trap boundary or caprock, limited buoyancy effect, complex oil-gas-water distribution, without obvious oil-gas-water interfaces, and relatively low oil (gas) saturation. Based on the simulation experiments of oil accumulation in low-permeability sandstone (oil displacing water), we study the migration and accumulation characteristics of non-Darcy oil flow, and discuss the values and influencing factors of relative permeability which is a key parameter characterizing oil migration and accumulation in low-permeability sandstone. The results indicate that: 1) Oil migration (oil displacing water) in lowpermeability sandstone shows non-Darcy percolation characteristics, and there is a threshold pressure gradient during oil migration and accumulation, which has a good negative correlation with permeability and apparent fluidity; 2) With decrease of permeability and apparent fluidity and increase of fluid viscosity, the percolation curve is closer to the pressure gradient axis and the threshold pressure gradient increases. When the apparent fl uidity is more than 1.0, the percolation curve shows modifi ed Darcy fl ow characteristics, while when the apparent fluidity is less than 1.0, the percolation curve is a "concaveup" non-Darcy percolation curve; 3) Oil-water two-phase relative permeability is affected by core permeability, fluid viscosity, apparent fluidity, and injection drive force; 4) The oil saturation of lowpermeability sandstone reservoirs is mostly within 35%-60%, and the oil saturation also has a good positive correlation with the permeability and apparent fl uidity.

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Nanocomposite pour point depressants (PPDs) provide a new way to further improve the fluidity of waxy crude oil at low temperatures, which has important application values in pipeline transportation. In this work, the effect of ethylenevinyl acetate (EVA) doped with magnetic spherical nanoparticles of Fe 3 O 4 (30 nm) on the morphology of wax crystals and the flow behavior of Daqing crude oil was investigated by polarized optical microscopy and rheological testing. The results showed that, compared to the EVA PPD doped with spherical nano-SiO 2 (with the same size), the EVA (VA = 28%)/Fe 3 O 4 nanocomposite PPD caused Daqing crude oil to have a more compact and regular wax crystal structure and a weaker gel structure because of the synergistic effect of magnetic materials and heterogeneous nucleation. This study examines the mechanism of nanocomposite PPDs and provides a new perspective for the development of new nanohybrid PPDs.

A terrestrial plant fruit extract was adopted to prevent hydrate accumulation. Four groups with different polarities, water-soluble, n-butanol-soluble, ethyl acetate-soluble, and petroleum ether-soluble portions, were obtained by prefractionation of the plant-extract hydrate antiagglomerant (AA). The hydrate antiagglomeration effect was tested in a high pressure transparent sapphire cell, and the active components were found mainly in the ethyl acetate-soluble portion that accounts for approximately 4.0% of the whole plant extract. Through further separation and purification, the five kinds of components obtained proved experimentally to have the effect of preventing hydrate agglomeration. Their molecules and structural formulas were inferred by the high resolution mass spectrum and nuclear magnetic resonance analysis. Compared with the spectrum library, the components were determined to be eriodictyol, apigenin, naringenin, luteolin, and 5-(4-hydroxy-6,7-dimethoxy-3-methyl­chroman-2-yl) benzene-1,2,3-triol. The tests on the extracted components and the commercial products verified their effect of preventing hydrate agglomeration, where apigenin and luteolin performed better than others.

The variation of the binodal temperatures for the different immiscible alloys, CdGa and BiGa, was determined through the dynamic viscosity measurements of melts under various external magnetic field conditions. The binodal temperature change was controlled by an energy barrier during solidification. An energy barrier equation is proposed to quantitatively calculate the activation energy during liquid phase separation process for the immiscible alloys. The relationship between the energy barrier and the magnetic field intensity has been established. The magnetic field not only causes an increase of melt viscosity for the immiscible alloys but also makes the melts becoming much stronger. The binodal temperature of the immiscible alloy obviously shifts to higher temperature as the magnetic field intensity increases. An anomaly that the viscosity of immiscible alloys decreases with decreasing temperature is uncovered.