Depleted hydrocarbon reservoir CO2 storage
Verified fundamental science of CO2 storage in Australia
Depleted hydrocarbon reservoirs are one of the main types of geological structure suitable for permanent storage of CO2. Re-utilisation of these reservoirs, in many scenarios, is a cost-effective solution for large scale CO2 geological storage.
Utilisation of depleted hydrocarbon reserves for CO2 storage
Re-utilisation of depleted oil and gas reservoirs are, in many scenarios, a cost-effective solution for large scale CO2 geological storage.
Verified fundamental science of CO2 storage in Australia
CO2CRC demonstrated that the CO2 can be safely stored and monitored in reservoirs that previously contained hydrocarbons
The research project
CO2CRC injected approximately 65,000 tonnes of CO2 -rich gas (Buttress gas) into the 25m thick Waarre Unit C sandstone within the depleted Naylor natural gas field at a depth of 2,000m in the Otway Basin, Victoria Australia.
Buttress gas, containing tracers to track dispersion and diffusion, was injected through injection well CRC-1 located at the flank of the reservoir at a rate of approximately 120 tonnes per day for 18 months. As modelled, the injected gas migrated up-dip to accumulate at the crest of the reservoir below the Flaxman formation (regional top seal). The Naylor-1 well, a legacy well on the structure (suspended gas producer) and located at the crest of the reservoir was used as the monitoring well. U-tubes were used to obtain downhole fluid samples during and after the injection and provided a direct measurement of storage efficiency.
Assurance monitoring included surveillance of the atmosphere, soil gas and shallow groundwater. To date, no tracer compounds have been detected above background levels in samples taken as part of the assurance monitoring program.
Results & outcomes
CO2CRC demonstrated that the CO2 can be safely stored and monitored in reservoirs that previously contained hydrocarbons. The research:
Validated technologies utilised to monitor CO2 storage sites (both deep and assurance monitoring).
Confirmed that modelling predictions for the storage project were reliable
Verified the fundamental science of CO2 storage in underground reservoirs.
Demonstrated that added gas tracers, including deuterated methane, krypton and sulphur hexafluoride can be successfully used to label stored CO2 for both monitoring and reservoir characterisation.
Validated a workflow for CO2 storage at field scale.
Verified the fundamental science of CO2 storage in underground reservoirs.
Demonstrated the ability of re-purposing existing wells.
Provided over eight years of geochemical analyses of the stored CO2 plume.
Confirmed that modelling predictions for the storage project were reliable
Established groundwater surveillance as useful in supporting the validation of safe storage of CO2.
Showed that analyses of well fluids obtained using a U-tube sampling system at over two km depth can provide information on the composition of the stored CO2.
Publications
Cook P. J Geologically Storing Carbon, Learning from the Otway Project Experience, CSIRO Publishing 2014.
Ashworth P, Rodriguez S and Miller A, Jenkins C, Case study of the CO2CRC Otway National Project, Energy Transformed Flagship, CSIRO, 2011.
Sandrine Vidal-Gilbert, S, Tenthorey E, Dewhurst, D, Ennis-King J, Hilli R, Geomechanical analysis of the Naylor Field, Otway Basin, Australia: Implications for CO2 injection and storage 2010, International Journal of Greenhouse Gas Control, Volume 4, Issue 5, 827-839
Underschultz, J., Boreham, C., Dance, T., Stalker, L., Freifeld, B., Kirste, D., Ennis-King, J., 2011. CO2 storage in a depleted gas field: An overview of the CO2CRC Otway Project and initial results. International Journal of Greenhouse Gas Control 5, 922-932.
Jenkins C, 2013, Statistical aspects of monitoring and verification, International Journal of Greenhouse Gas Control 13, 215- 229
Boreham, C., Underschultz, J., Stalker, L., Kirste, D., Freifeld, B., Jenkins, C., Ennis-King, J., 2011. Monitoring of CO2 storage in a depleted natural gas reservoir: Gas geochemistry from the CO2CRC Otway Project, Australia. International Journal of Greenhouse Gas Control 5, 1039-1054.
Dance T, Spencer L, and Xu J 2018 Geological characterisation of the CO2CRC Otway Project Site – What a difference a well makes.
Dance T, A Workflow for Storage Site Characterisation: A Case Study from the CO2CRC Otway Project Site. Conference Presentation AAPG 2009 Hedberg Conference.
Noble, R, Stalker, L, Wakelin S, Pejcic B, Leybourne M, Hortle A, Michal K; 2012, Biological monitoring of carbon capture and storage –’ A review and potential future developments. International Journal of Greenhouse Gas Control 10, 520 – 535
Utilisation of depleted hydrocarbon reservoirs for CO2 storage
CO2CRC demonstrated that the CO2 can be safely stored and monitored in reservoirs that previously contained hydrocarbons
Research topic
Flow assurance of CO2 in depleted reservoirs
CO2, injected into a subsurface formation with a pore pressure lower than the critical pressure, can cause several flow assurance issues including: loss of surface flow due to hydrate formation at the wellhead; tubing erosion caused by CO2 phase change; and impaired injection due to downhole hydrate formation plugging the reservoir.
Three case studies in the North Sea (P18-4, The Netherlands; Hewett, UK; and Goldeneye, UK) have been used to understand potential mitigations to these flow assurance issues.
Techniques such as dehydration, O2 removal, filtration and appropriate use of hydrate inhibition are recommended considerations to assist in preventing hydrate formation at surface. Similarly assuring that fluid density changes are minimized through wellbore architecture design will prevent flow assurance impacts downhole. A key recommendation is to further investigate the use of a downhole variable choking device to avoid the uncertainty of unstable phase behaviour occurring.
Research topic
Well integrity for existing active and inactive wells
Ensuring the integrity for wells, particularly those that were not designed for a CO2 storage operation, is a critical issue in CO2-DRS. Storage of CO2 adds further well integrity risk as CO2 changes the chemical conditions downhole which may alter wellbore materials.
CO2CRC has established criteria for assessing wells’ age, type/usage, cement condition, treatment, and P&A type. This is to be developed into a flow chart to assist a user in selecting the best approach for assessing and then addressing well integrity risk at specific sites.
Research topic
Geomechanical integrity assurance for re-inflation
It is recognised that reservoir-caprock systems do not behave perfectly elastically when subjected to depletion and subsequently CO2 injection. This mechanical change implies that the reservoir-caprock systems are unlikely to return to the initial state when pressurised, and geomechanical failure is a significant risk.
The understanding of the impact of reservoir depletion and then re-pressurisation is still in its infancy for CO2 storage. Data required to assess this geomechanical risk is rarely collected, and modelled outcomes are untested. From this study, a workflow to prevent, characterize and manage repressurisation risks has been developed. However, it is a key recommendation for this study that a broad data acquisition programme be developed for constraining geomechanics from the stress path point of view, and storage system limits against modelled predictions tested in the field.
Research topic
Enhanced hydrocarbon recovery for improved economics
CO2 Enhanced Gas Recovery (CO2-EGR), first proposed in the 1990s, has not received much attention due to the high price of CO2 at that time.
With advancements in CCS technologies and low emission incentives/regulations, CO2-EGR, in some cases, may be economically viable.
CO2CRC are developing criteria to enable the selection of potential field candidates for CO2-EGR. This study takes learnings from one of the few examples of EGR, K12-B in the Dutch sector of the North Sea.