The key objective of the CO2 WAG Pilots is to confirm improved sweep and to enhance oil recovery under CO2 WAG relative to water flooding. Two CO2 WAG Pilots are in progress in a giant Abu Dhabi Oil Reservoir. Each pilot has one horizontal producer and two horizontal injectors along with two vertical pilot observers. A detailed monitoring plan was designed and implemented to monitor pilots’ performance and track CO2 breakthrough and flow path. Injectivity of both water and CO2 was determined in the WAG cycles to investigate any loss of injectivity. The producers are being tested daily for oil rate, water cut, GOR using multi-phase flow parameters (MPFM) while portable test separators are used every quarter to validate these measurements. PVT analysis of produced fluids are being carried out on samples from portable test separators and MPFM sampling point to monitor CO2 content. Different gas and water tracers have been injected to trace the movement and breakthrough of injected fluids into the pilot producers. Carbon and oxygen-isotope analysis for produced and injected CO2 gas is also carried out to monitor CO2 breakthrough. RST logs in the observers demonstrate good sweep across different layers of the reservoir and show that WAG is providing mobility control to CO2. Several data sources were analyzed to determine CO2 breakthrough time and the CO2 flow path. Analysis of CO2 in produced gas has determined the timing of CO2 breakthrough. This is supported by the isotopic analysis of injected and produced CO2 in pilot producers and near-by producers. The tracer analysis results unambiguously identify the source of the produced CO2. Injectivity analysis of both CO2 and water showed injectivity of CO2 was either the same or higher than water injectivity. Moreover, no loss of injectivity was observed between WAG cycles. The pilot has been operated successfully without HSE issues since 2016. Corrosion logs are acquired within the extensive monitoring program along with inhibitor injection to avoid any Asphalting deposition. The paper discusses the performance of the first multi-well CO2-WAG pilots in a giant onshore reservoir in Abu Dhabi which is used to de-risk multiple CO2 WAG full field projects in ADNOC reservoirs. It also highlights the importance of the different reservoir monitoring tools for improved understanding of the pilots which will be used as a basis for implementing CO2 WAG for the full area development.

Carbon Capture and Storage (CCS) technologies help reduce carbon dioxide emissions from large point sources, such as power plants, gas processing facilities and other industrial facilities. It involves capturing CO2 emissions, transporting the captured CO2 to storage location, and securely storing underground for a long time. The term permanent storage is very often used. CCS technologies involving storage in underground geological formations are well established, and there are current a number of such ongoing projects, together with an increasing number of projects in the planning phase. Saline aquifers can be leading CO2 permanent storage candidates. Deep saline formations or deep brine reservoirs exist world wide, making them potentially accessible CO2 storage candidates. However, not all saline formations can be considered suitable for long term commercially viable storage candidates. A number of critically important factors must be taken into account/verified, for example, CO2 containment assurance, social and environmental impact, and project commercial aspects. A project feasibility is normally recommended as a first step, whereby potential saline aquifer candidates are screened, ranked against for example accepted best international guidelines and criteria. Detailed feasibility study can follow once top ranked suitable candidate(s) are identified. A comprehensive multi-discipline study was carried out looking at the potential for CO2 sequestration in deep saline aquifer formations within onshore Abu Dhabi. The area of interest is very large in scale (regional scale) and consists of multi stacked saline aquifer formations. The study has the added complexity that the same saline aquifer formations may be shared with near-by hydrocarbon exploration and production activities. The objectives were to analyze available geological data, oil field production and injection data, identify key constraining factors especially concerning CO2 containment assurance, arrive at regional storage capacity range estimates, and demonstrate site CO2 storage feasibility. Considerable amount of geological data and studies are available, which can assist with regional Onshore Abu Dhabi saline aquifer formation geological characterization for CO2 storage assessment. The characterization synthesis forms the study basis. Dedicated regional scale 3D saline aquifer formations compositional dynamic models were constructed, capturing the key CO2 sequestration processes/mechanisms. Storage capacity estimates were obtained from the dynamic model – the results will be published separately. A comprehensive Risk Assessment was carried out. Risk assessment approach and MMV plan development are shared.

CCS technologies are well established, many ongoing projects have proven to be safe and reliable. Saline aquifers can be leading CO2 permanent storage candidates. A comprehensive multi-discipline study was carried out looking at the potential for CO2 sequestration in deep saline aquifer formations onshore Abu Dhabi. The area of interest is large in scale (regional scale) and consists of multi saline aquifer formations. The study has the added complexity that the same saline aquifer formations may be shared with near-by hydrocarbon exploration and production activities. The objectives were to analyze available geological data, define screening, selection and ranking criteria, identify key constraining factors especially concerning CO2 containment assurance, and arrive at regional storage capacity range estimates. Considerable amount of geological data and studies are available, which can assist with regional Onshore Abu Dhabi saline aquifer formation geological characterization for CO2 storage assessment. The characterization synthesis forms the study basis. A benchmarking was conducted, published screening and selection processes were reviewed. By incorporating key formation geological characteristics, a list of potential formation candidates were generated. A new set of guidelines for large scale (regional saline aquifer) CO2 storage candidate screening is proposed, based on the earlier guidelines set out in DOE/NETL-2017/1844 (2017). Detailed considerations and evaluation during the screening process are presented. A new candidate ranking and selection matrix is proposed. Highest ranked candidates from the ranking and selection exercise were identified. Dedicated regional scale 3D saline aquifer formations static model was constructed, and compositional simulation model developed for CO2 sequestration capturing the key CO2 sequestration processes/mechanisms. Storage capacity estimates were obtained from the dynamic model - the results published separately. Large scale (regional saline aquifer) CO2 storage candidate screening, ranking and selection is a challenging process with many inherent uncertainties. It carries critical importance as the results and recommendations would pave the way for further feasibility or detailed studies and the definition of de- risking activities. It requires multi-discipline input and forms the corner stone for large CO2 storage project development. The study approach, new candidate screening guidelines, ranking and selection matrix may offer discernment for Operators planning similar assessments.

Carbon capture and storage (CCS) is recognized as an important technology in the decarbonisation of the energy system and saline aquifers are potential geological storage candidates. A major integrated feasibility study was conducted to screen and rank carbonate saline aquifer candidates for subsurface CO2 storage, onshore Abu Dhabi. The objectives were to obtain a range of potential CO2 storage capacities and annual injection rates and establish CO2 technical feasibility by integrating subsurface, well performance, cap rock integrity and economic analysis. A candidate screening matrix was developed taking into account onshore Abu Dhabi saline aquifer geological characteristics. Saline aquifers "A" and "B" within the syncline area were among the highest ranked candidates. A large-scale 3D static model was developed, utilising seismic and well data. Extensive CO2 storage simulation runs were performed, covering sensitivities and capturing major storage process/mechanisms applicable to carbonate formation. Combining geomechanics, geoscience, well performance, integrity and dynamic modelling, a CO2 storage site design was completed with slanted/horizontal injectors drilled radially from a centralised well pad. Ranges of CO2 storage capacity and maximum injection rates were obtained, depending on number of injectors and accounting for water offtake in nearby areas. Additionally, CO2 plume migration within several tens of thousands of years was simulated to aid CO2 containment assurance. Separate studies were performed to locate potential CO2 storage surface sites and used as part of the input for CO2 pipeline and surface facilities high level design. CAPEX, OPEX and abandonment cost estimates were generated as input for economic analysis. A multi-disciplinary risk assessment was performed, identifying potential risk factors throughout the life cycle of CO2 storage. De-risking and mitigation measures were considered and a detailed measurement, monitoring and verification (MMV) plan was developed. This paper presents the first integrated study on saline aquifer CO2 storage technical feasibility in this syncline area. A novel integrated workflow is employed, from initial candidate screening through dynamic modelling, surface facilities and risk assessment to recommendations for additional data acquisition. Key aspects which improved on published major international CO2 sequestration assessments are highlighted. The results and conclusions offer valuable insights for other Operators considering or planning CO2 sequestration in saline aquifer projects.