| In recent years, oil field development environment gradually extends to desert, ocean and polar in remote areas, and the oil field has the characteristics of deep reservoir, heavy oil and higher water cut. In order to reduce engineering investment, decrease wellhead back pressure and improve the ability of oil field production and resource utilization, single tube multiphase transportation process is often used for the gathering and transportation of produced fluid. In view of the environmental characteristics of Xinjiang desert oil field and produced fluid with high gas-oil ratio and water cut, it is therefore vital to research on the multiphase flow law of Xinjiang desert oilfield produced fluid in horizontal pipes.Based on the research advance investigation on related theory and technology of multiphase transportation at home and abroad, taking a typical desert crude-Shixi crude oil as the research object, its basic properties were tested and analyzed. According to multiphase gathering operation of Xinjiang desert oil field and extreme environmental ground temperature scope of the buried pipelines, a corresponding multiphase horizontal pipe flow experimental simulation device was set up to simulate the resistance characteristics and change laws of single-phase flow, oil-gas two phase flow, oil-water two phase flow and oil-gas-water three-phase flow in low temperature environment and analyzing the main influencing factors for the multiphase flow friction of Xinjiang desert oil. Considering partial of the physical parameters of multiphase transportation fluid are changing with the change of temperature and pressure, gathering pipeline was divided into several micro-tubes by thought of finite element, treated each tube with piecewise iteration, the multiphase flow pattern and corresponding pressure drop were predicted with Baker method. Considering the characteristics of gas joule-thomson effect and liquid friction heat production on temperature, multiphase transportation temperature drop prediction model was established and hydraulic and thermodynamic calculation function module of multiphase horizontal pipe flow were compiled with VB6.0, which proved its reliability with examples. It has important practical significance for the Xinjiang desert crude oil gathering security in low temperature environment.The results show that the Shixi crude oil belongs to light waxy crude oil with the density of812.3kg/m3at20℃, its wax content is5.8%and the condensation point is14℃respectively. The abnormal point of Shixi crude oil is25℃. It follows as power-law fluid rheological model with shear thinning behavior when the oil temperature is lower than abnormal point. When Shixi crude oil flows as single-phase, pipe pressure drop increases with the increase of oil flow rate. When the environment temperature and oil flow rate ranged from15℃to0℃and0.37m/s to0.42m/s, or-5℃and0.30m/s to0.37m/s, respectively, the single-phase horizontal pipe flow pressure drop may have a slight decrease, out of that range it will still increase with the increase of oil flow rate. The lower environment temperature will cause greater pressure drop under the same flow rate. The pressure drop increases significantly when it reduced to5℃. The pressure drop of single-phase crude oil in the stainless steel pipe is97.4%higher than that in the organic glass pipe under the same condition and depositing of wax crystal on the wall along the flow direction increased gradually, the most deposition exists in the outlet of test pipe. Under certain experimental condition, the effect of increased flow velocity is significantly greater than its drag reduction effect and the oil-gas multiphase transportation pressure drop are higher than that in the single phase flow. Under the same oil superficial velocity, pipe pressure drop increases with the increase of gas superficial velocity. When the superficial gas velocity is higher than1.32m/s, pressure drop increases significantly. When the superficial gas velocity is the same, the faster the superficial oil velocity is, the greater the flow pressure drop will be. Reverse phase point of oil-water emulsification under the oil-water flow condition is about45%. When the added water content is lower than the reverse phase point, the oil-water flow pressure drop increases with the increase of the added water content. Conversely, the pressure drop reduces significantly with the increase of the added water content and improving water temperature reduced the pressure drop effectively. Under the same liquid superficial velocity, the pressure drop of the oil-gas-water three phase multiphase transportation increases significantly with the increase of the gas superficial velocity. Under the certain gas superficial velocity, the greater liquid superficial velocity means greater multiphase transportation pressure drop. When the oil flow and gas flow are the same, the pressure drop of oil-gas two-phase flow are56.2%higher than that of oil-gas-water three-phase flow generally and the differences between them are bigger when the gas-oil ratio is higher, therefore, adding appropriate amount of water to the oil-gas two-phase flow in pipeline can improve the fluidity to a certain extent. The compiled thermodynamic and hydraulic calculation function module of multiphase flow has sufficient theoretical basis, the predicted value shows good agreement with the literature data, the average relative error between the predicted values and the experimental measurements is31.81%, the relative errors are much lower for the moderate gas contents. |
