Influences of Different Modes of Reservoir Heterogeneity on Performance and Oil Recovery of Carbon Dioxide Miscible Flooding

摘要

The main goals of this study are to investigate the influences of different modes of reservoir heterogeneity on oil recovery by supercritical CO2 miscible flooding.The investigated heterogeneity modes include different (1) single-fractured reservoirs of different inclination angles,(2) permeability configurations of layered reservoirs,and (3) sequence of permeability distributions in composite reservoirs.Complete reservoir rock and oil compositional analyses were performed.The minimum miscibility pressure (MMP) of oil-CO2 was mathematically calculated using several empirical correlations and experimentally determined using slim tube tests.The core flood tests were achieved using actual fluids injected through 12 actual reservoir rock samples.Four samples of different fracturing angles as single-fractured reservoirs,four samples of different permeability configurations as layered rocks,and four samples to represent composite reservoirs.The slug size of supercritical CO2 was optimized to be 0.15 pv,injected,and chased by actual reservoir brine through these different simulated modes of reservoir heterogeneity.The results indicated that all different modes of reservoir rock heterogeneity have a crucial influence on oil recovery by CO2 miscible flooding in carbonate oil reservoirs.Noteworthy,unfractured reservoirs produced higher oil recovery by CO2 miscible flooding than that one of single-fractured ones.An oil reservoir of 30 degree inclination angle of single fracture produced the highest oil recovery while fractured rocks of 45 degree fracture produced the minimum one in this category.The rock permeability sequences of medium-low-high (MLH) mode for composite reservoirs and medium-high-low (MHL) distribution mode for layered reservoirs are highly recommended for CO2 miscible flooding.The results have proven the suitability of the CO2 application for layered and composite heterogeneous carbonate reservoirs and do not recommend this EOR process for single-fractured reservoirs.They have also shown a real impact of the reservoir heterogeneity mode prevailing in the reservoir under development on oil recovery by this EOR process.