## 4 Experiments and Analysis  
### Experimental Facility  
The CCS consists of a cylindrical metal layer electrode and a central electrode rod in parallel in circuit, which are both sensitive to the change of the retention rate of oil and water components in the flow runner space, as shown in Figure 16. The ring space between the inner wall of the metal electrode and the built-in electrode rod is the flow runner of the combined capacitance sensor, that is, the fluid flow region. The photo of the CCS we made is shown in Figure 17. The polyimide was used as the insulating layer.  
In order to verify the effectiveness of the CCS in practical measurement, a dynamic experiment was carried out on a horizontal oil-water two-phase flow experimental facility in the Petrodaqing Test and Experiment Center of Logging and Testing Technology. The flow experimental facility is shown in Figure 18, which consisted of a water tank, an oil tank, a separation tank, two horizontal peristaltic metering pumps, two plexiglass testing pipes with a diameter of 125 mm and 20 mm, a  
Figure 16: Mechanical structure diagram of the CCS.  
Figure 15: The static responses of the CCS, CYS, and COS for the W/O flow pattern.  
high-speed camera, and the combined capacitance instrument. The pipe with the diameter of 125 mm was used to measure the water cut using the combined capacitance instrument. The pipe with the diameter of 20 mm was used to observe the flow pattern using the high-speed camera. The combined capacitance instrument was made up of the CCS, the umbrella-type flow collector, and the circuit. In the measurement, the fluid including oil and water phases was collected by the umbrella-type flow collector and flowed into the CCS. The Swiss MacroVis high-speed camera named SpeedCam was used in the experiment. A CMOS color sensor was built into the camera. Full resolution recording time was 3.3 s. When the maximum dynamic output pixel is 1280 \(\times\) 1024, the picture update rate is 1000 frames/s, and when the minimum output pixel is 1280 \(\times\) 10, the picture update rate can reach 93,282 frames/s. In this experiment, according to the velocity of flow, the frame rate was set from 2100 frames/s to 3000 frames/s, and the output pixels range from 1280 \(\times\) 350 to 1280 \(\times\) 500.  
In the experiment, water from the water tank and oil from the oil tank through peristaltic metering pumps were pumped into the plexiglass testing pipe. The mixed fluid was collected through the umbrella-type collector and flowed into the CCS to measure the water cut. Then the fluid passed through the plexiglass pipe with the diameter of 20 mm and was photographed by the high-speed camera to obtain the flow pattern. Finally, the mixed fluid flowed into the separation tank and was separated by density difference, so that it could be recycled. The experimental medium was tap water and D110 white oil. The density of water is 1 g/cm\({}^{3}\), and the density of D110 white o  
Figure 17: Photo of the CCS: (**a**) sectional view; (**b**) overall view.  
Figure 18: Schematic diagram of experimental facility for horizontal oil–water two-phase flow in Petrodaqing Test and Experiment Center of Logging and Testing Technology.  
The reason for the use of tap water is that due to the long-term water injection development in Daqing Oilfield, the mineralization degree of oilfield brine is reduced from 6000 to 2000 ppm, which is basically the same as that of tap water. Thus, the small difference between tap water and brine has little effect on the results.  
Considering that the measurement results of the instrument were influenced by the repeatability errors of measurement and system errors for long time continuous operation, the horizontal oil-water two-phase flow experimental facility was used to carry out the segregated flow experiments multiple times using the experimental point where the flow rate was set as 3, 5, 10, 15, 20-60 m\({}^{3}\)/d by a step of 10 m\({}^{3}\)/d, and the water cut was set as 0-1 by a step of 0.1.