## 4 Experiments and Analysis
### Calibration Experiments under Different Temperatures and Pressures  
Since the temperature and pressure of oilfield fluid is different from that on the ground, the calibration experiments were first carried out to investigate the response characteristics of the CCS under different temperatures and pressures. In the calibration experiment of temperature, the CCS was placed in an oil-filled or water-filled measuring cup in the oven. The temperature of oil was raised to 125 \({}^{\circ}\)C, and the temperature of water was adjusted to 80 \({}^{\circ}\)C. The capacitance values of the CCS were measured under different temperatures in the oil and water, respectively. The calibration results are listed in Tables 2 and 3. From the analysis of the results, the capacitance values of the CCS in the pure water phase are obviously larger than that in the pure oil phase, which was consistent with the simulation results. Moreover, the capacitance value of the CCS does not change obviously at different temperatures, which shows that the CCS has a good temperature performance. In the calibration experiment of pressure, the combined capacitance instrument was put into the pressure simulation well filled with diesel oil in the Petrodaqing Test and Experiment Center of Logging and Testing Technology. The pressure was set as 15, 25, and 40 MPa. The calibration results were obtained and listed in Table 4. It can be seen from the results that with the increase of pressure, the frequency response values had the tendency to increase slightly, but the change was not obvious. The maximum deviation of the response value was not more than 1.2%, which verifies the pressure stability of the instrument. in Figure 19b, the interface between oil and water is obvious and irregular. With the increase of the velocity of the oil-water mixture and the difference of the oil-water viscosity, during the development of the flow pattern, the difference of the oil-water velocity resulted in a particularly obvious fluctuation in the interface, but no obvious droplets were formed. For dispersed flow that includes dispersion of oil in water and water flow (DO/W&W), as shown in Figure 19c, in aqueous solution, there are some oil bubbles or slug in the upper part of the pipe. The bottom is water. Figure 19d is the oil in water emulsion (O/W), where oil is dispersed in water by oil bubbles and slug-shaped large oil bubbles. Water in oil emulsion and oil in water emulsion (DW/O&O/W), is shown in Figure 19e. When the water cut is low, the water phase exceeds the bearing capacitance of the oil phase with the increase of the flow velocity, and some oil droplets are dispersed in the water. For water in oil and water flow (DW/O&W), as shown in Figure 19f, when the flow rate of oil and water is low and the oil cut in the oil/water mixture is high, some water droplets in the oil phase are distributed in the upper layer of the pipe, and the water phase is distributed in the lower layer of the pipe due to gravity action. Water in oil (W/O) is shown in Figure 19g. Water is in the dispersed phase, and oil is in the continuous phase. It mainly occurs in the flow conditions of high flow and low water cut, where the water phase is dispersed into droplets and evenly dispersed in oil. The distributions of different flow patterns with a flow rate and a water cut were obtained experimentally, as shown in Figure 20a. The flow pattern distribution of the oil and water phase velocity calculated by flow rate and water cut is shown in Figure 20b. From the figure, we can clearly obtain the relationship between the flow pattern of the horizontal oil-water two-phase flow and the flow rate, water cut, and the velocity of each phase. Through the analysis of the flow patterns of the horizontal oil-water two-phase flow, the response characteristics of capacitance sensors under different flow patterns can be obtained experimentally. Figure 19: Seven horizontal oil–water two-phase flow patterns obtained by high-speed camera.