The emulsification of heavy oil and water into a W/O emulsion would increase the viscosity of the W/O emulsion and reduce the mobility of heavy oil. As we know, addition of a viscosity reducer such as water-soluble surfactants could change the status of emulsion and improve the mobility of heavy oil. Although up to 90% viscosity reduction could be achieved in laboratory experiments, field improvement of the heavy oil recovery is not satisfactory with addition of a viscosity reducer. Actually, it is related to the difference of the mixing process of water-soluble viscosity reducer, water, and heavy oil between lab experiments and subsurface flow in the formation. The viscosity of heavy oil is significantly affected by the temperature and emulsification. As for the heavy oil sampled from Bohai Oilfield, its viscosity decreases by 95% when the temperature increases from 50 to 100 °C. At 50 °C, the viscosity of the W/O emulsion with 70% water content is up to 21.05 times that of the dehydrated heavy oil. In the emulsification process of the W/O emulsion, water molecules disperse into heavy oil and agglomerate together to form water droplets, and the number of water droplets increases when the water content is increased. When we add some amount of a water-soluble viscosity reducer to the W/O emulsion, the re-emulsification process or the way of addition of the water-soluble viscosity reducer has a great effect on the variation of the state and viscosity. When heavy oil is mixed with 30% content of water-soluble viscosity reducer solution (the reducer content is 1% of the emulsion), up to 98% reduction in the viscosity of heavy oil could be obtained. However, when the W/O emulsion with 30% water content is mixed with 1% water-soluble viscosity reducer, only 4% reduction in the viscosity of emulsion is observed. In the re-emulsification process of water in a W/O emulsion with addition of a reducer, pieces of heavy oil containing a number of water droplets are separated by the reducer solution and a W/O/W emulsion is generated. The pieces of heavy oil containing water droplets in such a W/O/W emulsion are much larger than the heavy oil droplets in an O/W emulsion. As the heavy oil in the reservoir is in the state of a W/O emulsion, a W/O/W emulsion with large heavy oil pieces containing water droplets will be generated when a water-soluble viscosity reducer solution is injected, and the resulted viscosity reduction is much lower than expected based on conventional lab experiments. Consequently, the experiments related to heavy oil with addition of a water-soluble viscosity reducer should be carried out with the W/O emulsion.

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Summary In the steam-injection processing of unconsolidated heavy-oil reservoirs, the pore space may change because of the overburden pressure increase and wormhole generation. Meanwhile, injected high-temperature steam can result in mineral dissolution and alteration and consequent diameter change of sand particles and pore space. To obtain a better and more thorough understanding of permeability variation characteristics during the steamflooding process, a series of experiments with sand-packed tubes was designed and conducted. On the basis of quantified experimental data, a numerical model was built by taking various permeability variation mechanisms into consideration. Reservoir simulations were consequently carried out to study the permeability distribution variation on the field scale and its impact on oil recovery. The results showed that with increasing overburden pressure, the permeability and porosity of the sand tube were both decreased. Permeability decrease ranged from 35 to 54%, and porosity decrease was approximately 5%. The partial permeability was increased by more than four times when a wormhole was generated at the outlet. The permeability and porosity of sand-packed tubes were increased because of mineral dissolution in the steamflooding process. Particle migration and mineral dissolution resulted in permeability variation and formation of a high-permeability region in the reservoir, which enhanced the heterogeneity of the reservoir. The high-permeability region mainly formed at the upper layer of the reservoir in the vertical direction and on the line between steam injection and oil production wells in the horizontal direction. Permeability variation exacerbated the steam channeling, which resulted in more remaining oil and a lower oil recovery rate of the reservoir. When permeability variation was considered in a numerical simulation, the cumulative oil production for 4 years was decreased by approximately 7000 m3, and the oil recovery rate was decreased by 4.3%.

The mullet Liza haematocheila is widely distributed in low-salinity waters around the world and has high economic value. However, details regarding the foraging ecology of mullet larvae remain unclear. Larvae of L. haematocheila were sampled in Laizhou Bay of the Bohai Sea, China, in May 2016, and diet composition was detected using gut content analysis to compare differences in feeding parameters and diet shift in dominant prey during ontogeny. The results showed no linear relationship between gape size (GS) and standard length (SL) at larva length <7 mm (flexion larvae, FL), but linear increase was observed for SL >7 mm (post-flexion larvae, PFL). Maximum prey size (MPS) overlapped with GS during the FL stage but was never higher than GS during the PFL stage. Trends of increasing MPS and prey size range (PSR) during the PFL stage were lower than those during the FL stage, but prey number (PN) increased significantly during the PFL stage. Diet composition analyses in mullet larvae showed a total of 10 mesozooplankton species (or categories), of which 8 species were copepods (including copepods nauplii and copepodites), and showed the dominance of 4 small copepods (<1 mm). Analyses of the numerical proportion of dominant copepods showed that the largest prey (Paracalanus parvus) gradually increased as GS increased; conversely, the smallest prey (nauplii of Calanus sinicus) decreased. Collectively, these results suggest that PFL tends to exhibit increased PN but not prey size or size range, and diet shifts from smaller to larger prey during ontogeny in mullet larvae. All these indicate that PFL has higher prey selection ability compared with FL, specifically switching the diet to include larger small copepods during the PFL stage and increasing the prey number instead of increasing prey size. These determine the importance of small copepods in mesozooplankton as dominant prey and facilitate predictions of the impact of climate change on mesozooplankton and fish larvae.