Abstract
CO2 EOR (enhanced oil recovery) will be one of main technologies of enhanced unconventional resources recovery. Understanding effect of permeability and fractures on the oil mobilization of unconventional resources, i.e. tight oil, is crucial during CO2 EOR process. Exposure experiments based on nuclear magnetic resonance (NMR) were used to study the interaction between CO2 and tight oil reservoirs in Chang 8 layer of Ordos Basin at 40 °C and 12 MPa. Effect of permeability and fractures on oil mobilization of exposure experiments were investigated for the different exposure time. The oil was mobilized from matrix to the surface of matrix and the oil recovery increased as the exposure time increased. The final oil recovery increased as the core permeability increased in these exposure experiments. Exposure area increased to 1.75 times by fractures resulting in that oil was mobilized faster in the initial stage of exposure experiment and the final oil recovery increased to 1.19 times from 28.8 to 34.2%. This study shows the quantitative results of effect of permeability and fractures on oil mobilization of unconventional resources during CO2 EOR, which will support CO2 EOR design in Chang 8 layer of Ordos Basin.
Highlights
CO2 EOR will be one of main technologies of enhanced unconventional resources recovery
This study shows the quantitative results for effect of permeability and fractures on oil mobilization of tight sandstone cores exposed to CO2 in Chang 8 layer of Ordos Basin
nuclear magnetic resonance (NMR) T 2 spectrum amplitude gradually reduced as exposure time increased
Summary
CO2 EOR (enhanced oil recovery) will be one of main technologies of enhanced unconventional resources recovery. Understanding effect of permeability and fractures on the oil mobilization of unconventional resources, i.e. tight oil, is crucial during CO2 EOR process. This study shows the quantitative results of effect of permeability and fractures on oil mobilization of unconventional resources during CO2 EOR, which will support CO2 EOR design in Chang 8 layer of Ordos Basin. CO2 EOR has been recognized as a potential way to enhance tight oil reservoirs recovery and to reduce CO2 emissions and greenhouse gas effects[5,6]. In order to select befitting well and to optimize CO2 fracturing design and to determine the C O2 enhanced oil recovery parameters, it is necessary to understand the effect of permeability and fractures on oil mobilization of tight oil reservoirs exposed to CO2
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