| Oil-water two-phase flow and gas-oil-water three-phase flow are commonly encountered in the petroleum and nature gas industry. Study on the oil-water two-phase flow and oil-gas-water three-phase flow, especially the characteristics of flow patterns and pressure gradient, can solve many important technical problems for petroleum industry. It is also very important for the improvement of the theory of multi-phase flow and practical application. In this paper, characteristics are investigated systemically for oil-water two-phase flow and gas-oil-water three-phase flow in horizontal pipes with inner diameter of 50mm and length of 40m. The main contents and conclusions of the research are the following.(1) By analysis of visual observation, photos, videos, the acquired signals of conductance probes and pressure transducer, integrating with static analysis (PDF analysis), it is found that oil-water two-phase flow in horizontal pipes can be classified into nine flow patterns: SM flow, SW flow, DOSW flow, ST-MI flow, O-DO/W-W flow, DO/W-W flow, O-DO/W flow, O-DW/O flow and DO/W flow. The transform boundary correlations of some flow patterns are obtained through dimensionless variable analysis, which coincide well with experimental data. Flow pattern maps are plotted with mixture velocity vs. input water cut and oil superficial velocity vs. water superficial velocity. Furthermore, another flow pattern map is also plotted with oil phase dimensionless number vs. water phase dimensionless number in order to strengthen the common suitability of the pattern map.(2) Gas-oil-water three-phase flow is the couple of gas-liquid flow and oil-water flow. According to this characteristic, new names of gas-oil-water three phase flow patterns are presented. Twelve flow patterns are identified, which are SM‖SM flow, SW‖ST flow, SW‖IN flow, SW‖DW/O&DO/W flow, IN‖ST flow, IN‖O&DO/W flow, IN‖DO/W&W flow, IN‖O&DW/O flow, IN‖DO/W flow, AN‖O/W flow, AN‖W/O flow and AN‖DW/O&DO/W flow. Also by analysis of visual observation, photos, videos, the acquired signals of conductance probes and pressure sensors, integrating with static analysis (PDF analysis), phase distribution and flow characteristics of these flow patterns are described in detail. Flow pattern maps are plotted with liquid superficial velocity vs. gas superficial velocity under different ratios of oil and water flowrate and the mechanism on flow patterns transition is analyzed. Another flow pattern map is also plotted with liquid phase dimensionless number vs. gas phase dimensionless number under different ratios of oil and water flowrate., but the common suitability of which need to be studied further.(3) Compared with Mandhane's and Taitel&Dukler's gas-liquid flow pattern map, it is found that the region of wavy stratified flow increases apparently for the gas-oil-water three-phase system when input water cut in liquid is less than eighty percent. The region expanded is the region of SW || IN flow pattern that oil-water two phase takes on intermittent flow regime. SW || IN flow pattern is transformed from IN || DO/W flow pattern when input water cut in liquid is higher than 50 percent and from SW || ST flow pattern when input water cut in liquid is lower than 50 percent. For low gas flowrate, the transition from SM || SM flow pattern to IN || ST flow pattern"moves"downward as oil faction and superficial gas velocity are increased.(4) An intensive study on characteristics of mean pressure gradient, water holdup, and height wetted by water on the pipe wall for oil-water two phase flow and gas-oil-water three-phase flow is conducted. The following regularity is obtained.The pressure gradient for oil-water flow increases nonlinearly with the increase of mixture velocity. While mixture velocity is higher than 0.566m/s, corresponding to the phase inversion point, a sharp peak in pressure gradient appears. Combining with the analysis of flow pattern transition, the input water cut at phase inversion point is around 60%. The relational equations that water holdup is influenced by input water cut and mixture velocity are obtained before and after phase inversion point. Two fluid model is used to predict the pressure gradient and water holdup for oil-water separated stratified flow under the condition of curve interface and plane interface, and the predicted data is compared with the experiment data.For the gas-oil-water three phase flow, the pressure gradient under different input water cuts in liquid increases with the increase of gas and liquid superficial velocities. Corresponding to the phase inversion point, a sharp peak in pressure gradient also appears at some gas and liquid superficial velocities. It is found that the input water cut of the phase inversion point for three phase flow which is around 40%, is obviously lower than that for two phase flow, which is around 60%. At high liquid superficial velocity or at low liquid superficial velocity with higher input water cut in liquid over 50%, the water holdup takes on the trend to damped exponentially. A new term, height wetted by water on the pipe wall, is put forward.. Influences of gas and liquid superficial velocities and input water cut in liquid on it are analyzed.(5) Cross-correlation technology is used for the study of the characteristics of the interfacial wave velocity about stratified flow regime and annual flow regimes for gas-oil-water three phase flow. The results show that the wave velocity of the gas-oil interface and oil-water interface of SW‖ST flow pattern, the gas-liquid interface of AN‖DO/W flow pattern and AN‖DW/O flow pattern increase with the increase of gas superficial velocity and liquid superficial velocity on the condition of fixed ratio of oil and water flow rates. When liquid superficial velocity or gas superficial velocity is fixed, the velocity of gas-oil interface of SW‖ST flow pattern decreases while the velocity of oil-water interface of SW‖ST flow pattern increases with the increase of input water cut in liquid, and the higher the input water cut, the bigger the increase amplitude. For AN‖DO/W flow pattern and AN‖DW/O flow pattern, the wave velocity of gas- liquid interface also increases. No regularity is obtained for the wave velocity on gas-liquid interface for SW‖IN flow pattern due to the intermittent flow between oil and water, but the characteristic parameters of oil-water intermittent flow, such as the water slug velocity, the water slug length and the water slug frequency, are of regular variation with liquid superficial velocity, gas superficial velocity and input water cut in liquid.
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