Study On Density Variation Of CO₂ Mixture In Geological Storage

As a result of increasing greenhouse gas emissions,the global warming has accelerated in recent years.Consequently,it is imperative to reduce the release rate of CO2 to mitigate greenhouse effect.Recognized as a promising way to ensure cost-efficient avoidance of CO2 emission to the atmosphere,CO2 capture and storage(CCS)consists of separating CO2 from the emission sources and transporting and storing the captured CO2 underground.Furthermore,CO2-enhanced oil recovery(EOR)has been increasingly adopted in large-scale CO2 storage projects for its commercial advantages.To design and optimize the CO2 displacement process,properties such as density,phase behavior,and viscosities of mixtures of CO2 and hydrocarbons must be known.Undecane is a mid-length chain alkane and a typical component of crude oil.Thus,the properties of CO2 + undecane mixture are of great research value.Also,the captured CO2 comprises different impurities,including N2,O2,Ar,Sox and so on.These impurities have harmful effects on CCS projects.Densities of compressed CO2 + undecane binary mixtures were measured using a magnetic suspension balance(MSB).Measurements were made at temperatures ranging from 313.15 to 353.15 K and pressures ranging from 8 to 19 MPa at CO2 concentration(x)of 0,0.2483,0.4641,0.6797,and 0.8874.The mixture densities were found to increase linearly with pressure and decrease with temperature.The mixture densities show a crossover with composition when the CO2 mole fraction is high.With the increase of CO2 mole fraction,the mixture densities increase at first,then decrease.The increase of pressure makes the excess molar volume less negative,whereas the increase of temperature makes it more negative.Densities calculated from PHSC EOS with improved parameters are in good agreement with the experimental densities.Adopting the constant binary interaction parameter kij for different alkanes in the PHSC EOS slightly enlarge the model deviation but simplifies the calculation.And densities of CO2+N2+O2 mixed gas was also measured at 293.15-353.15 K,5-18 MPa.The non-condensable impurities caused the critical pressure of CO2 mixed gas decreased.Compared to lower temperature,no density mutation occurred at higher temperature in the experimental pressure range as the pressure increased.The calculated normalized capacity achieved a minimum value at a certain pressure.To reduce the adverse effects of impurity gases,the impure CO2 should be stored in deep reservoirs,where the temperature is high and the pressure is beyond the minimum capacity pressure.