Study On The Thermodynamic And Transport Properties For CO₂ Enhanced Oil Recovery

CO₂ enhanced oil recovery?CO₂ EOR?is one of the most effective techniques in tertiary oil recovery.CO₂ EOR not only can enhance oil recovery but also sequestrate CO₂ into the depleted petroleum reservoir.A key parameter in designing an efficient miscible gas flooding is the minimum miscibility pressure?MMP?,which was crucial for successful CO₂ EOR.CO₂ EOR was divided into miscibility and immiscibility according to the MMP.The interfacial tension?IFT?between crude oil and CO₂ was zero at miscibility status.Simultaneously,the oil recovery was obtained the maximum value.Therefore,IFT also plays an important role in CO₂ EOR design and application.The design and application of CO₂ EOR technology was based on the accurate MMP and IFT.The experiments and models for MMP and IFT were studied in this work.First of all,a set of apparatus with the vanishing interfacial tension?VIT?technique was designed and manufactured.To test and verify the reliability of the apparatus,the IFTs of CO₂ + n-C₁₀H₂₂ system were measured and compared with the values in literatures.The results proved that this apparatus was reliable and could be used to measure IFT accurately for CO₂ EOR systems.The MMPs of three simulated oils at different experimental conditions were measured by VIT method.Numerous MMPs for various crude oils at different experimental conditions were collected from literatures.According to the injection gas composition,the MMPs were divided into three categories: pure CO₂,CO₂ mole fraction less than 0.5?2<0.5?and CO₂ mole fraction larger than 0.5?2>0.5?in injection gas,respectively.The influence factors of MMPs were analyzed and three MMP equations were established for pure CO₂,2<0.5 and 2>0.5 in injection gas.The average absolute relative deviation?AARD?are 5.85 %,4.06 % and 6.49 %,respectively.A total of 215 data points for paraffin + CO₂ and 202 data points for paraffin + mixture gas?CO₂ and N2?were measured by the apparatus manufactured in this work.Numerous paraffins IFTs were collected from literatures.IFT models were proposed for pure CO₂ and mixture gas injection.The models were the function of temperature,pressure,the carbon number and injection gas composition.The new models can predict the IFTs accurately.The models combined with mixing rules were used to estimate gasoil MMPs precisely.The AARD were 4.45 % and 7.77 % for simulated oils and crude oils.In addition,the density gradient theory combined with PR equation of state was studied in this work.The influence factors?c?of paraffins and CO₂ were obtained from the experimental IFTs by this theory.The c models were proposed based on the influence factors of c.The new models were used to estimate IFTs for five CO₂ + paraffins binary systems in this work.The average absolute error?AAE?were 0.97 m N/m,0.84 m N/m,1.80 m N/m,2.55 m N/m and 2.49 m N/m for five binary systems,respectively.At last,150 data points of paraffins IFTs for CO₂ injection modified by ethanol were measured and the paraffins IFTs correlation for the systems was proposed.The IFTs of paraffins for CO₂ injection modified by ethanol were compared with pure CO₂ injection.The results proved the paraffins IFTs were decreased obviously for adding ethanol in CO₂.The MMPs of simulated oils for CO₂ injection modified by ethanol were predicted by the correlation and mixing rules,and compared with the MMPs for pure CO₂ injection.The results indicated the MMPs can be reduced obviously with ethanol as the modifier for CO₂ EOR systems.