| Most well areas of Daqing peripheral oilfields are already in the late exploitation period,with a relatively low gas-oil ratio of produced liquid,and the water content is in the medium and high range.Within the gathering and transportation radius,it has a small pressure fluctuation,generally higher than the saturation point,with the result that the light components all dissolve in the crude oil,which mainly exists in the form of saturated live oil during pipeline transportation.In the past design process of gathering and transportation system,the flow characteristics of dead oil were usually taken as the main basis for the process design of gathering and transportation pipeline,without considering the influence law of dissolved gas on the crude oil corresponding properties during the actual pipeline operation process,which brought great uncertainty to the production of live oil.In view of the above problems,a set of high-pressure tubular live oil flow characteristic measurement system is established in this paper,which indirectly drives the experimental fluid by using the methods of alternating driving of high-pressure and low-pressure oil tanks,maintaining the pressure of back pressure valve and automatic switching of control valve,so as to avoid the over pump shear in the process of fluid transportation and solve the problem that the shear rate fails to be quantified in the traditional experimental device,which makes the fluid only affected by the shear of pipe wall.A set of controllable temperature aqueous live oil pipe flow experimental system is established.The separator and gas injection system are added on the basis of the conventional indoor controllable temperature experimental loop.Through the switching of open and closed processes,the flow characteristics of miscible oil-water two-phase flow,oil-water separated phase flow and closed dissolved gas oil-water two-phase flow can be tested respectively,which provides an experimental basis for the in-depth study of the rheology,two-phase flow pattern and pressure drop variation law of aqueous live oil.Taking the crude oil in Ta 21-4 well area of Daqing as an example,the rheology of live and dead oil is tested by using the rotary rheometer and the above-mentioned high-pressure tubular live oil rheology measurement system.The effects of temperature and flow rate on the fluidity of which are explored.It is found that the pipeline pressure drop gradient of live and dead oil varies logarithmically with temperature and linearly with flow rate.Live oil has lower viscosity and better flow characteristics,which is due to the continuous filling of dissolved light components between oil,water,wax crystals and other molecules,expanding the distance between molecules and weakening the interaction between crude oil molecules to a certain extent.In addition,the consistency and difference of the above two measurement methods are demonstrated.Compared with the high-pressure loop method,the shear principle based on the rotary rheometer is different from the real flow physical process,resulting in the lower the temperature,the greater the measured viscosity deviation.The experiments of oil-water miscible flow characteristics,oil-water separated phase flow characteristics and closed dissolved gas oil-water two-phase flow have been completed successively on the pipe flow experimental loop of controllable temperature aqueous live oil.Using the analysis method of combining high-speed camera and data acquisition system,the flow state of mixed liquid in the pipe is divided and summarized.By changing the experimental conditions,the transition criteria between different characteristic flow patterns are clarified,and the flow pattern diagram of aqueous live oil is drawn;the effects of water content,flow velocity and temperature on the pressure drop gradient along the loop during the flow process are discussed.The differences between the oil-water miscibility experiment and the oil-water phase separation experiment on the pressure drop along the loop are compared:compared with the oil-water miscible flow,the pressure drop gradient along the loop during the oil-water phase separation experiment is lower,which is closely related to the emulsification degree of oil-water The pressure drop law of oil-water two-phase flow in dissolved gas state is explored,the influence mechanism of dissolved gas volume and temperature on pressure drop gradient is analyzed,and the low-temperature gathering and transportation limit of crude oil under different wellhead temperatures is given.Based on the mass and momentum conservation equation of dissolved gas oil-water twophase,considering the shear force of liquid relative to the pipe wall,moreover combined with the liquid treatment method of BB model section and Bendiksen friction formula,a hydraulic model of aqueous live oil on the basis of mechanical properties is constructed,and the effects of the water content,liquid flow,ambient temperature and dissolved gas rate on hydraulic and thermal characteristics of pipeline transportation process are analyzed.The applicability analysis of the model to the crude oil physical properties is completed through the back calculation of the pipeline starting point pressure.The change trend of the relative error of the aqueous live oil pressure calculated value before and after gas dissolution is consistent as a whole,which is maintained within 15%,and the accuracy meets the actual requirements of the project.In this paper,the pipe flow experimental characteristics and theoretical model research of aqueous live oil are carried out.The obtained rheological characteristics of crude oil,oil-water two-phase flow pattern,pressure drop variation law and hydro-thermal analysis and calculation method can provide a useful theoretical and technical basis for the safe and economic transportation of aqueous live oil. |
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