Carbon Dioxide Storage in High Asphaltene Content Oil Reservoirs
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AbstractCarbon dioxide storage in high viscosity and density hydrocarbon reservoirs that have high asphaltenes content is attractive. However, CO2 is an asphaltenes insoluble solvent, hence, CO2 injection into these reservoirs is expected to cause asphaltenes deposition. In pore-scale, how the deposition of asphaltenes would impact the CO2 trapping and consequently CO2 storage is not known. This study proposes highly efficient trapping and storage of CO2 in high-asphaltenes content reservoirs. Our recent experimental studies on CO2 flooding into bitumen reservoirs revealed with Scanning Electron Microscopy (SEM) images that CO2 gets trapped in asphaltenes phase. The CO2 trapping is occurred both in residual and displaced oil due to mainly the presence of clays in the reservoir rock. The CO2-displaced oil interaction promotes the formation of foamy oil. As the size of the CO2 bubbles in the displaced oil increases, the CO2 storage capacity of the displaced oil is enhanced. The bubble size is mainly controlled by the CO2 injection rate and the bigger CO2 bubbles in the displaced oil are obtained at lower CO2 injection rate. Hence, CO2 trapping in high asphaltenes content reservoirs can be more effective if the oil reservoir has high clay content and when CO2 storage is achieved through low injection rates. However, because low injection rates provide more interaction time for asphaltenes and CO2, asphaltenes deposition may occur near injection well and deposition of asphaltenes may inhibit the further propagation of CO2 which may limit the reservoir CO2 storage capacity. It should be also noted that the optimum CO2 injection rate for storage purpose can be different for every reservoir and hence, should be determined experimentally.
