Study Of Downhole Phase State Distribution For Carbon Dioxide Flooding Based On Fibre Sensing

The oil recovery is getting lower and lower, in the mid-late period of oilfieldexploitation. Carbon dioxide flooding can not only greatly improve the recoveryfactor of oil and gas fields, but also can solve the problem of carbon dioxidesequestration. It is necessary to study and analyze the downhole supercritical carbondioxide phase distribution of carbon dioxide flooding, in order to improve oilrecovery efficiency and provide a theoretical basis of the wellhead carbon dioxideinjection parameters settings, for the injection of carbon dioxide flooding projects.Therefore the numerical model of phase distribution for carbon dioxide floodingmust be established. In order to verify the accuracy of the numerical model, it isnecessary to monitor the wellbore phase distribution during the carbon dioxideinjection for full distribution, and the monitoring of temperature and pressureparameters is particularly important. However, the conventional down-holetemperature and pressure monitoring means cannot achieve distributed real-timeonline monitoring on the temperature and pressure of the wellbore carbon dioxidefluid in the process carbon dioxide injection.This paper established the distribution of temperature and pressure couplednumerical model along the wellbore in the process carbon dioxide injection, basedthe theory of heat transfer, with the application of the energy conservation law,combined with the numerical method of carbon dioxide physical parameters. TheMATLAB iterative calculation procedure has been composed based on discretenumerical model. The distribution curve of the temperature and pressure in thecarbon dioxide injection wellbore can be obtained after setting the reasonablewellhead and injection parameters, based on which the down-hole carbon dioxidephase distribution map can also be drawn. The graphical user interface has beencomposed based on the MATLAB program for the convenience of the user.To demonstrate the accuracy of the downhole phase distribution numericalmodel for carbon dioxide flooding established by this paper, the Raman optical fibertemperature sensor and the Brillouin optic fiber pressure sensor were determined torespectively monitor the downhole data of temperature and pressure after theanalysis of the principle on optic fiber temperature and pressure sensor monitoring.The fiber sensor was wrapped with reasonable package for the complexenvironment in the carbon dioxide injection wells and the shortcomings of fiberslender and fragile. The analysis and calculation of sensitivity of the temperatureand pressure multi-interface transfer on the encapsulated fiber sensor was carried onwith the application of heat transfer theory and the theory of elasticity. Thecalibration tests of temperature and pressure were finished to obtain encapsulated fiber sensor performance indicators.The appropriate wellhead layout scheme was developed and the temperatureand pressure of the carbon dioxide injection test well were monitored using thephase monitoring system based on distributed optical fiber sensing for carbondioxide flooding. The monitoring data were analyzed and processed, and then thecomparison with the theoretical data after the MATALB iterative computation wasobtained to verify the accuracy of the numerical model of the downhole phasedistribution of carbon dioxide flooding. The relationship between the injectionparameters and the distribution of downhole carbon dioxide phase state wasanalyzed with carbon dioxide flooding downhole phase distribution numericalmodel established by this paper, in order to improve the efficiency of carbon dioxideinjection, obtain the ideal effect of oil displacement, also provide the necessar ytheoretical basis for the set of process parameters for the injection of carbon dioxide.