Study Of Flow Characteristics Of Heavy Oil Solution Gas

Oil solution gas drive technology is widely used in heavy oil development.After the gas dissolves in the heavy oil,it is lifted to the surface of the gathering pipeline.As the pressure is reduced,gas gradually evolves.Studying the flow characteristics of heavy oil solution gas has important guiding significance for the actual operation of pipelines.This article has conducted in-depth research on the flow characteristics of heavy oil solution gas.The main research contents and conclusions are as follows:The high-temperature and high-pressure experiment system without pump shear was designed and developed by ourselves.The system can complete the study of heavy oil solution gas sampling,dissolution characteristics testing,flow characteristics testing,wax deposition testing,stop transmission and restart testing,etc.The system has the characteristics of no pump shearing,variable flow,and stable flow.The system solves the problem that the shear rate cannot be quantified in the conventional experimental device,and can more accurately reflect the true flow state of the fluid.Based on the study of the dissolution characteristics of CO₂,combined with local sampling,micro-photograph,differential pressure fluctuation analysis and other methods,the flow pattern of heavy oil solution gas in the horizontal pipe was studied.The results showed that the flow pattern of heavy oil solution gas was mainly heavy oil solution gas single-phase flow and disperse system of heavy oil solution gasµ-bubble at low dissolved gas volume,and intermittent flow begins at high dissolved gas volume.With the increase of dissolved gas volume,the flow transition boundary gradually shifted to high pressure.In addition,due to the high viscosity of heavy oil,the flow pattern is relatively less affected by temperature and flow rate.Based on the study of flow pattern and flow pattern conversion,the pressure drop characteristics of heavy oil solution gas in horizontal pipelines and the change of apparent viscosity of heavy oil solution gas were analyzed.The rheological model was established.The results show that the development process of heavy oil solution gas in pipe is greatly affected by the pressure and is less affected by temperature and flow rate.Comparing the viscosity of heavy oil solution gas under different conditions shows that the viscosity reducing effect of microbubbles is lower than that of heavy oil solution gas.Analysis of the viscosity of the system under different conditions shows that high dissolved gas volume,high temperature,high pressure and appropriate flow rate is conducive to the delivery of heavy oil solution gas.When the system pressure is near the saturation pressure,the viscosity of the system is the lowest.The power law model was used to describe the fluid rheology,and the apparent viscosity equations of the heavy oil,heavy oil solution gas and disperse system of heavy oil solution gasµ-bubble were established.The foam mass was further related to the rheological index and consistency coefficient of the dispersion system.The variation characteristics of microbubbles in the dispersion system are studied by local sampling and microscopic photographing.The results show that honeycomb structure is formed after heavy oil solution gas degassing in static state.The distribution of microbubble particles is found to be approximately Gaussian distributed.Analysis of the variation of particle size of micro-bubbles shows that it decreases with the increase of pressure and flow rate,while the temperature has little effect on it.The micro-bubble characteristics are further related to the viscosity of the system,and it is found that the small particle size and the large number of micro-bubbles are beneficial to the decrease of the viscosity of the system.Based on the Einstein hard-ball model and the Mitchell conventional foam model,considering the effect of the dissolved gas volume and the microbubbles on the viscosity of the dispersed system,the viscosity prediction model of disperse system of heavy oil solution gasµ-bubble was established.The model can provide theoretical guidance for engineering practice and is of great significance to improve the theory of multi-phase flow.