Combined injection and separating device for parallel sand filling pipe was used as experimental equipment, including constant flux pump, intermediate container, high permeability sand pack, low permeability sand pack, incubator, PMU and collector. Experimental oil was compounded according to the viscosity of formation oil in Bohai X oil field. Experimental water was compounded according to the analytical data of formation water and injecting water provided by working field.

Based on the basic experimental scheme, three groups of contrastive experiments was designed by different permeability, matching degree of particle size and concentration of emulsions to study the influence of the profile control effect (Table 1). Permeability ratio was introduced to evaluate the longitudinal heterogeneity. Sand-filling pipe model was used to carry out the experiment of emulsion flooding, in which the emulsions have different droplet diameter. In the process of experiment, particle size matching factor was adopted to evaluate the matching relation between the emulsions and porous medium particles in the following formula:

R = d m d e (1)

In which, R is the particle size matching factor; d_m is the pore diameter of porous medium; d_e is the diameter of the emulsion droplet.

The pressure of Initial water flooding and Emulsion flooding was measured under constant flow condition, the yield of water and oil of the sand filling pipe was measured. The experimental steps are as follows: First, the sand filling pipe was made, in which the air permeability was measured after oil washing and drying. Then the process of filling water to saturation state was done, after which the oil flooding was finished, the bound water was produced. Second, based on the basic scheme, the two sand filling pipes was paralleled, the process of water flood was done with constant speed of 3 mL/min. In this process, the data of pressure and production of each sand filling pipe was recorded. Third, the

process of oil washing and salt washing was done, then the bound water was produced again. The emulsion flooding experiment was in progress with the same flooding speed. Then the data of pressure and production of each sand filling pipe was recorded. Fourth, based on the contrastive experiments, the first step to the third step was repeated.

In order to analyze the profile control characteristics of emulsions and to comparatively analyze follow-up experiment，the basic experiment was designed to carry out water flooding experiment and emulsion flooding experiment. Then the distributing rate of low permeability pipe was recorded to analyze its increased range. The results of the experiment are shown in Figure 1. From which we can know that, in the process of emulsion flooding, the distributing rate of low permeability pipe obviously increased, this proved that the emulsions would referential access to the high permeability and less resistance layer. When the resistance of displacement front became large enough, the follow-up emulsions would access to the low permeability and high oil saturation layer, then the residual oil of low permeability layer could be displaced. By the change of pressure

gradients in emulsion flooding, we can know that the process of “plugging, plugging removal and plugging” often happened when the emulsions were transporting in the sand filling pipes. The distributing rate and pressure of emulsions both fluctuated, but the changing trend of them was the same. The larger the distributing rate of low permeability pipe was, the larger the seepage resistance was. Conversely, the lower the seepage resistance was, the lower the pressure was. This proofed that temporary plugging of emulsions was the primary cause of the profile control characteristics. Because of the temporary plugging, the emulsions would move to the deeper layer, which made the residual oil moving, then the recovery rate was increased.

Figure 2 showed the change of the distributing rate in low permeability pipe with different permeability gradation. The larger permeability gradation was, the better the profile control characteristics of emulsions were. The reason was that the plugging strength of emulsions was very strong with a low demulsification rate in the high permeability layer. So that the emulsions would enter the low permeability layer, in which the demulsification of emulsions happened because of the shear action. This inclined the seepage resistance of emulsions to become lower in the low permeability layer. Then a large number of emulsions and follow-up liquid flowed out from the low permeability pipe.

Figure 3 showed the change of the distributing rate in low permeability pipe with different matching degree of particle size. For the diameter of the pore, the bigger the particle size of the emulsions was, the better the profile control performance of emulsions was. But for the real test, the bigger the particle size of

the emulsions was, the bad the stability of emulsions was. So when the emulsions were used for profile control, based on the stability of emulsions was better, we should choose the emulsions with a suitable diameter.

Figure 4 showed the change of the distributing rate in low permeability pipe with different concentration of emulsions. The higher the concentration of emulsions was, the larger the distributing rate was. As a result the profile control performance of emulsions became better. When the emulsions were migrating in porous medium, the pore and the throat would be plugged by the droplets of emulsions. At the same time, the follow-up fluid continued to flow, which caused the accumulation of the droplets in the core. Then the profile control performance of emulsions became better. The higher the concentration

of emulsions was, the more obvious accumulation effect was, the better the profile control performance of emulsions were.