Study On Prediction Of Temperature And Pressure Of CO₂ Injection Wellbore

CO₂ flooding has been widely concerned as a more effective means of improving recovery factor.On the one hand,after CO₂ reaches the bottom of the well and enters the reservoir,it is necessary to achieve miscibility to achieve the optimal oil displacement effect,and achieving miscibility requires a certain pressure,which requires the pressure prediction and control during the injection of CO₂ into the wellbore.On the other hand,during gas injection construction,the injection pressure at the wellhead can often only be monitored,and the bottomhole pressure cannot be directly obtained unless the instrument is run to measure,which will undoubtedly increase the cost.These two reasons prompted us to carry out prediction research on the pressure distribution in the wellbore,and obtain a reasonable CO₂ injection wellbore temperature and pressure prediction model.This paper studies the flow and heat transfer behavior of CO₂ from the physical properties of CO₂.On the basis of the equation of state published by the predecessors,the theoretical calculation and error analysis were used to select the CO₂ physical parameter calculation method.The Span-Wagner equation was used to calculate the CO₂ density,isobaric specific heat,and the Joule Thomson coefficient,Fenghour method to calculate CO₂ viscosity.And borrow the experimental data in the literature to verify the existing friction calculation formula,and through the error comparison and experimental data fitting and other means to obtain the most accurate calculation method of supercritical CO₂ friction coefficient.Based on the law of conservation of momentum and heat transfer theory,the pressure drop model and heat transfer model of the gas-liquid two-phase one-dimensional stable flow in the wellbore are established.The effect of heat transfer on the total heat transfer coefficient of the wellbore revised the heat transfer model.Based on the above,a wellbore temperature and pressure coupling calculation model considering the changes of CO₂ physical parameters was established,and the temperature and pressure profile of the wellbore was solved iteratively.The prediction model was applied to Y22-46 gas injection wells in Y oilfield.It is verified by the measured data that the average relative error of temperature is 1.8%,and the maximum error is 4.45%,with the bottom hole error is 4.45%;Meantime the average relative error of pressure is 0.7%,while the maximum error is 3.6%,with the bottom hole error is 3.6%.The prediction is accurate and meets the engineering requirements.Finally,the prediction model is used to analyze the sensitivity of the injection parameters,and the conclusion has certain guiding significance for on-site construction.