Optimising the transition from CO2 EOR-EGR towards CCS for a mature oil and gas reservoir

Abstract

This study evaluates carbon dioxide enhanced oil recovery (CO2 EOR) for enhanced oil recovery (EOR), enhanced gas recovery (EGR) and carbon capture and storage (CCS) purposes in the mature Mereenie Oil and Gas Field (‘Mereenie’). Mereenie consists of a rim oil and gas cap reservoir with low aquifer activity. We evaluate the microscopic and macroscopic displacement efficiencies of CO2 EOR techniques after determining the minimum miscibility pressure of the CO2 and reservoir oil system. Investigations on EOR, EGR and CCS are then conducted on a sector model containing the main pay zones. The CO2 flood, water alternating gas (CO2 WAG) and Huff ‘n’ Puff methods are evaluated within three strategies: unstructured well placement, five-spot pattern configuration and gravity-assisted flood. The sector model shows performance of an immiscible process in oil and gas recovery and CO2 storage potential. The CO2 flood is efficient in oil recovery but less efficient in CO2 utilisation, making it a good option for a half oil recovery–half CO2 storage objective. The CO2 Huff ‘n’ Puff is more efficient for oil recovery at early stages of operation, and also very efficient for gas recovery. The CO2 Huff ‘n’ Puff technique is not a good option for the CO2 storage objective. The CO2 WAG could be a good technique for oil recovery and CO2 storage with proper CO2 slug size and WAG ratio. The five-spot pattern configuration enhances sweep efficiency. The gravity-assisted flood strategy can be appropriate for the rim oil reservoir with gas cap in Mereenie.