In order to solve the technical problem of injected fluid channeling in offshore oilfields,the basic performance evaluation of plugging agent,core hole plugging rate and the large⁃scale dominant channel treatment experiment of "plugging + profile control" oil increase and precipitation effect was carried out in Bohai reservoir. The results show that the blocking rate of blocking agent for large⁃scale dominant channel is higher than 90%,which indicates that it can meet the technical requirements of blocking large⁃scale dominant channel in Bohai reservoir.Combining the large⁃scale dominant channel plugging technology with chemical profile control and flooding technology,the dual effects of macro and micro fluid flow diversion can be obtained,and the effect of oil increase and precipitation is very obvious.Compared with hydrophobically associating polymer solution,although the viscosity of Cr3+ polymer gel is relatively low,the polymer molecular aggregates in Cr3+ polymer gel have "intramolecular" cross⁃linking structure characteristics,and have better compatibility with reservoir pores,which can establish an effective displacement pressure gradient in deep core,resulting in better fluid diversion effect and larger recovery.

Aiming at technical demand on relieving the reverse of imbibition profile, displacement effect of alternate injection of Cr3+ polymer gel and water was studied, taking reservoir of Bohai oilfield as simulation object, regarding injection pressure, water content and recovery efficiency as evaluation index. Results showed that as the displacement agent flowed into the medium and low permeability layer, on the one hand, the swept volume was magnified. On the other hand, seepage resistance and start up pressure of imbibition were increased, thus resulting in the reverse of the imbibition profile. Once the alternate injection of Cr3+ polymer gel and water was adopted, polymer solution could get priority to flow into the high permeable layer and block off it, then subsequent water flowed into medium and low permeability layers to displace the oil. Therefore the phenomenon of the reverse of imbibition profile was relieved or even eliminated. Once the alternate injection of C3+ polymer gel and water was conducted in A22 injection well in LD5 - 2 Oilfield, injection pressure get increased, which was good for enlarging sweep volume effect.

The foaming ability, viscosity, stability and microstructure of the weak gelSD foamer composite systems were studied by rheology, cylinder measurement, scanning electron microscopy (SEM) and microscopy. The results demonstrated that the properties of weak gelSD foamer composite systems was improved obviously compared to the single flooding technology. When halflife period of the compounded system became longer, and the viscosity of foam increased, the foam stabilitywas enhanced. In the weak gelfoam composite system, an adsorption film of weak gel on the foam was formed easily, which meant that the foam was wrapped in the inside. The interfacial viscosity between gaseous and liquid phases was enhanced, preventing the foams to coalescence and breakup. Therefore, the viscosity and stability of foam were reinforced and the halflife period became longer.

The influence of salinity on the shape, size and plugging property of crosslinked polyacrylamide microspheres were studied by nuclearpore film filtration experiment and sandpacked model, rheology and dynamic light scattering. The results show that the microspheres with different salinity all plug effectively. The experiments of sandpacked model showed that the salinity has little effect on the plugging properties, and not affects the plugging depth in the model at all. The viscosity of microspheres dispersed system increased with the increasing of shear rate, which displayed the minimal dilatants liquid property, and the salt concentration had little influence on the rheology of crosslinked microspheres. When the salinity increased, the microspheres had more stereo sense and smaller size, but these are only small changes.