Abstract
CO2 storage mechanisms in an EOR process in mature reservoirs are measured to determine three types of storage factors, which are introduced into compositional numerical simulation. The hybrid objective function coupli ng the oil recovery factor and the CO2 storage ratio is proposed to optimize the injection and production parameters in CO2 flooding. Three storage factors of the oil and water partition coefficient, the permeability change coefficient and the CO2 retention factor are measured in a laboratory, which is utilized to modify the grid properties of oil, brine, rock in compositional numerical simulation. The restart procedure is automatically adopted to consider these storage mechanisms in CO2 EOR. The bi-objective function of the oil recovery factor and the CO2 storage ratio is used to optimize the injection and production parameters for CO2 EOR, which concludes the design principles on CO2 EOR and storage. The oil and water partition coefficient defined as the ratio of the CO2 solubility in the oil phase and the brine phase is a constant for a specific reservoir condition. The permeability change coefficient caused by the mineral dissolution effect of carbonate water decreases slightly in the early stage and increases gradually with the long term injection. The CO2 retention factor that is induced by the relative permeability hysteresis decreases with the pressure and the permeability. These equivalent treated methods that modify fluids and rock in the real-time are inserted into the procedure of compositional numerical simulation to take into account the storage mechanisms in CO2 EOR. The results show that the effect of the storage mechanisms on EOR is evident. Furthermore, the bi - objective optimization indicates that the injection rate should be reduced largely in the medium and the later stages to control gas channeling as the EOR scenario is focused. And the bottom wellhole pressure of producers should be decreased to the lower level to maximize oil recovery. As the storage scenario is concentrated, the injection rate is required to be slightly controlled. As the producers are shut off, the injection rate must be increased significantly to maximize CO2 storage. The storage mechanisms in the CO2 EOR process have not been understood thoroughly. The methodology of numerical simulation coupling CO2 EOR and storage is not mature, which is still not taken into account in commercial software. The results above provide a way to optimize CO2 EOR and storage simultaneously, which is significant for the large scale storage after CO2 EOR in mature oilfield.
Research progress of biological effects of cell membrane under infrared and terahertz irradiation