A decade of CO2 injection into depleting oil fields: Monitoring and research activities of the IEA GHG Weyburn-Midale CO2 Monitoring and Storage Project

Injection of CO2 into the Weyburn Oil Field, Saskatchewan, Canada, began October 2000 and 10 years later approximately 18 MT of CO2 will have been stored in the geological reservoir. The CO2 injection is part of an ongoing enhanced oil recovery effort that will extend to 2035 and likely beyond. Both Weyburn and the adjacent Midale oil field are highly suitable for CO2-EOR and it is expected that, combined, more than 40 MT CO2 will eventually be stored in these carbonate reservoirs. Currently about 2.4 MT and 0.4 MT CO2/year are being stored in the Weyburn and Midale fields, respectively, which now represent the largest site of monitored geological storage of CO2 globally. The Weyburn Field is operated by Cenovus Energy and the Midale Field by Apache Canada. The anthropogenic CO2 used at Weyburn-Midale is a by-product of coal gasification at the Great Plains Synfuels Plant in North Dakota, USA. The compressed CO2 is delivered to the oil fields through a 323 km pipeline that crosses the international boundary. The IEA GHG Weyburn-Midale CO2 Monitoring and Storage Project was established prior to the onset of CO2 injection at Weyburn to assess monitoring methods and subsurface processes associated with the injection of CO2 into geological storage sites. This research program is now in its second phase of research. Baseline 3D seismic surveys were performed over the Weyburn Field before injection and subsequent repeat 3D seismic surveys have been taken during the course of injection spanning multiple years and have indicated that CO2 distribution within the reservoir can be imaged seismically. Similarly, repeat reservoir fluid sampling surveys have monitored a range of chemical and isotopic parameters to help identify processes associated with CO2-rock interaction. In addition, multiple soil gas and shallow hydrology surveys have been performed during the past 10 years with no indication of CO2 reaching the surface. The current research program is building on many of the results obtained during the first phase of work on the Weyburn Field. For example, some of the current research includes applying stochastic methods to relate fluid chemistry to the seismic data to better characterize the distribution of CO2 in the subsurface. Additional methods of modeling CO2 distribution post-injection are also being demonstrated and integrated into several risk assessment methodologies. A detailed well database has been developed to catalogue characteristics associated with wells drilled at various stages of field development using different cementing practices and completion methods to assist with providing parameters for long-term modeling of well behaviour. In addition, a downhole well integrity testing program to examine cement sheath characteristics will be implemented in two wells in each of the fields. In summary, more than 30 research studies are being performed within this phase of the program to examine aspects of site characterization, well integrity, geochemical and geophysical monitoring methods and risk assessment. One of the goals for the work from this research program is to provide a best practices manual for the transition of CO2-EOR sites into storage sites. This paper provides an overview of the studies and results developing from the research program.

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