Geological performance evaluation of CO2 sequestration in depleted oil reservoirs: A simulation study on the effect of water saturation and vertical to horizontal permeability ratio

Human consumption of fossil fuel as a primary source of energy has led to the net increase of anthropogenic carbon dioxide (CO2) emission into the atmosphere. The magnitude of its contribution to global warming and climate change is unprecedented. Carbon capture and storage (CCS) in geological formations technology has merged as the key approach towards potential CO2 sequestration, and depleting oil and gas reservoirs appear to be promising candidates. Various researchers studied the concepts and processes about reservoirs' performance upon CO2 injection and storage with little attention on variations of reservoir water saturation and permeability ratio (vertical versus horizontal permeability). In this study, with the use of 3-dimensional (3D) numerical simulations the safe and long term evaluation of reservoir performance on CO2 storage in terms of storage capacity, trapping mechanism, injection rate, and operational pressures were performed at Liaohe basin, China. Results revealed that CO2 stored in a supercritical form was dominant of all and that at the end of 100 years more than 70% of injected CO2 existed as free gas in supercritical form, the tendency which decreased to less than 65% after 1000 years of its storage. Conversely, the storage of CO2 in trapped and dissolved forms was increased by 6% and 3% respectively. The results from this work provide valuable insights on CO2 phase relative storage potentiality for enhanced and safe CO2 storage in a depleted oil reservoir. It also provides an improved long term CO2 storage sequestration strategy which incorporated hysteresis metrics. The study recommends an optimum CO2 storage scheme with controlled pressure buildup in a depleted oil reservoir.