1. Permanent CO 2 storage in depleted gas fields combined with CO 2 enhanced gas recovery (EGR) Idar Akervoll, SINTEF Petroleum, Trondheim Contribution to safe storage of CO 2 Increased use of depleted gas fields for permanent CO 2 storage will directly help shortening the time to realisation since such formations have an already proven storage capacity with cap rock that can store buoyant gasses over geological time periods. This will allow a shortening of the storage site characterisation time prior to start of CO 2 injection. Safe long-term CO 2 storage due to proven tight seal is an advantage although some specific integrity issues deserve some attention. CO 2 storage capacity estimates for the Norwegian North Sea indicate that abandoned gas fields have equal or higher capacity than oil fields, thus being a significant storage resource. Introduction Objectives The main goal of the project is to increase the understanding of how mobile water saturation in gas reservoirs will improve the permanent CO 2 storage potential, reduce CO 2 back production as well as increase the EGR potential from the reservoir. The secondary objectives are: To acquire dynamic reservoir parameters through laboratory measurements, ready to be scaled up for use in field scale reservoir simulation to estimate the influence of variable water saturation in reservoir layers and apply the increased understanding and acquired dynamic parameters in reservoir simulation of a field scale case. Scope of work Figure 1 Comparison of log-derived water saturation (SW) with hyperbolic fit based on height above Free Water Level (-3860 m TVDSS) and porosity (SW_EH) for well K12-B02 for the Slochteren Sst (CASTOR Deliverable 3.3.1 Improved_geol-model_K12B). Acknowledgements: This project will be supported by CLIMIT and GDF SUEZ. A second industry partner (domestic) has stated promising interest to support the project. NTNU will be a partner responsible for the PhD student. References CSLF; Carbon sequestration leadership forum: "2013 Carbon Sequestration Technology Roadmap", http://www.cslforum.org.http://www.cslforum.org Clemens, T., Secklehner, S., Mantatzis, K.; Jacobs, B.: "Enhanced Gas Recovery, Challenges Shown at the Example of three Gas Fields", SPE 130151, SPE EUROPEC/EAGE Annual Conference and Exhibition, Bracelona, Spain, 14-17 June 2010. NPD; Norwegian Petroleum Directorate: "CO 2 Storage Atlas for the Norwegian Contenental Shelf", April 2014. Geel, K. and Duin, Ed, TNO: "CASTOR-D3.3.1 Improved geological model of the K12B Gas Field", TNO 12 February 2005. The project will mainly target gas fields with mobile water, with and without an active aquifer providing pressure support. The research work is based on an integrated approach involving physical laboratory experiments at elevated pressure and temperature to acquire dynamic flow parameters and data on gas trapping saturations as well as mobilization of the same. The data will be input to reservoir simulation models for matching laboratory performance, upscaling to field scaled and prediction of field performance on real cases. The lead time for qualification of a geological formation for use as a CO 2 storage site has been pointed to as one of the major obstacles for fast adoption of CCS as a climate change mitigation option (CSLF, 2013). The CO 2 storage capacity in depleted gas fields can be increased by continued hydrocarbon (HC) gas production (CO 2 EGR), and in this way contribute positively to the economy of CCS (Clemens et al.). In order to correctly evaluate this possibility and devise an optimal injection strategy to address this issue, more knowledge is needed regarding: Methods to improve sweep of the gas reservoir Dynamic mixing behaviour of the injected CO2 Pore-scale mechanisms for replacing capillary trapped HC gas with CO2 Methods for modelling of miscible gas-gas displacement processes at field scale Frontiers of knowledge According to the CO 2 Storage Atlas for the NCS issued by NPD, the abandoned (and depleted) Frigg gas field has a large potential for CO 2 storage due to remaining gas in the field itself and a huge aquifer that is connected to the field. The reservoir simulation exercises on field models of Frigg show that there is a higher potential than what is simulated if the pressure increase is compensated with more water production out of the aquifer (NPD, 2014).