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).
Nishikiori, Nobuo (Norske Shell A/S) | Sugai, Keiichiro (Arabian Oil Co. Ltd.) | Normann, Clas (Talisman Energy Norge AS) | Onstein, Arne (Talisman Energy Norge AS) | Melberg, Oddbjoern (DONG Norway) | Eilertsen, Terje (DONG Norway)
This study describes an improved engineering workflow to perform technical evaluation and screening of gas injection EOR. A successful case study demonstrates how field data, engineering analysis and simulation are integrated to precisely model gas injection EOR. This workflow can be adaptable for any type of reservoir and can be utilized as a fast-track screening workflow for gas injection EOR.
The target for this study was the Gyda reservoir located in the southern part of Norwegian North Sea in the Norwegian Continental Shelf. The reservoir is of heavily faulted heterogeneous shallow marine sandstone. As the measure of heterogeneity, a Dykstra-Parson's coefficient1 (VDP) of more than 0.8 has been measured from core plug data.
For the purpose of building a tool that can be utilized for gas injection EOR study, a five-step workflow has been implemented:
The results of this case study confirmed the capability of the described workflow to model gas injection EOR for the heterogeneous sandstone reservoir. Potential gas channeling in high permeability streaks and an improved displacement by gas was precisely modeled by the workflow. Injection strategies, such as WAG, SWAG and gas injection have been screened by the model, leading to a conclusion in relatively short period of time.