Effect of Stratification on Segregation in Carbon Dioxide Miscible Flooding in a Water-Flooded Oil Reservoir

A. A. Bhatti, S. M. Mahmood, Bilal Amjad


Oil reservoirs are subjected to tertiary recovery by deploying any enhanced oil recovery (EOR) technique for the recovery of left over oil. Amongst many EOR methods one of the widely applied worldwide is CO2 flooding through miscible, near miscible or immiscible displacement processes. CO2 flooding process responds to a number of reservoir and fluid characteristics. These characteristics have strong effect on overall efficiency of the displacement process. Better understanding of the effect of different characteristics on displacement process is important to plan an efficient displacement process. In this work, the effect of stratification resulting in gravity segregation of the injected fluid is studied in an oil reservoir which is water-flooded during secondary phase of recovery. Sensitivity analysis is performed through successive simulation on Eclipse300 (compositional) reservoir simulator. Process involves the continuous CO2 injection in an oil reservoir with more than 1/3rd of original oil in place left after water flooding. Reservoir model with four different permeability layers is studied. Four patterns by changing the arrangement of the permeabilities of the layers are analysed. The effect of different arrangement or stratification on segregation of CO2 and ultimately on the incremental oil recovery, is investigated. It has been observed that out of four arrangements, upward fining pattern relatively overcame the issue of the segregation of CO2 and consequently 33% more oil with half injection volume is recovered when compared with the downward fining pattern.

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