Traditional EOR approaches intend to minimize the injected CO2 to reduce the high cost of the purchased gas, while this approach does not satisfy the sequestration objective to maximize the CO2 stored in the reservoir by the end of the flooding period. In this paper, a new approach is presented where, a methodology is developed to optimize both EOR and sequestration processes.

CO2 injection into a North Sea chalk field is studied using a compositional reservoir simulator. We have investigated the effect of six parameters including injection scheme, injector and producer well type, well control mode, slug size and the WAG ratio on the coupled CO2 EOR and sequestration process. Three different injection strategies using either pure CO2 or a mixture of CO2 and hydrocarbon gas including WAG, continuous CO2 injection and soak alternating CO2 injection have been investigated.

Three well configurations are considered. It includes a vertical and two horizontal well options completed in the third and fifth layer of the reservoir. We have considered BHP and rate control as effective well control modes.

Experimental design is used to perform an efficient sensitivity analysis on the mentioned parameters. Two objective functions have been defined, aimed at co-optimization of EOR and sequestration processes while respecting the economy of the process through minimizing recycled CO2.

In this work a methodology / approach has been developed, which could be applied to other fields. In the case studied here, the results show that the water alternating gas injection scheme using a mixture of CO2 and hydrocarbon gas to be the optimum case (EOR and sequestration process).

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