An integrated geophysical, geodetic, geomechanical and geochemical study of CO2 storage in subsurface reservoirs

It is possible to capture emissions of CO2 from coal-fired power plants and store them in deep subsurface reservoirs such as mature oil reservoirs. This Carbon Capture and Storage (CCS) technology has demonstrated the potential to reduce mankind’s greenhouse gas emissions while meeting the world’s energy needs. Furthermore, if CCS allows the development of the next generation of clean coal power plants, it will be worth an estimated £6.5billion to the U.K. economy, creating 100 000 jobs, as part of the new ‘green economy’. However, to guarantee security of storage, monitoring methods must be in place that can track the movements of CO2 through the subsurface, and image the effects of CO2 injection on the subsurface rocks. When CO2 is injected into reservoirs, the pressure changes can lead to expansion of the reservoir, resulting in deformation of both the reservoir and the overlying rocks that provide the seal. Geomechanical deformation can cause problems at CCS sites if faults and fractures open, allowing CO2 to escape from the target reservoir. I propose a study of geomechanical deformation at CCS sites, using geophysical techniques to monitor deformation, and generating computer models to simulate deformation. Fractures in the caprock will generate seismic energy, which can be detected on geophone arrays. By detecting these microseismic emissions, it is possible to determine how the subsurface is responding to CO2 injection. The inflation of the reservoir can push up overlying rocks, causing uplift of the ground surface, which can be monitored with satellites. My project will analyse microseismic events detected at two CCS sites – In Salah, Algeria, and Weyburn, Canada. I will also study high quality surface uplift data at In Salah. By locating the hypocenters of microseismic emissions, it will be possible to identify regions where deformation is occurring, and, if events cluster onto discrete surfaces, to identify actively deforming faults in the subsurface. The identification of active faults is crucial for understanding the geomechanical deformation above the reservoir. The locations of microseismic events can be compared with observations of surface uplift to paint an overall picture of the deformation induced by injection. I will use event locations and surface deformation to calibrate and benchmark geomechanical models, distinguishing between models that do a good job of predicting microseismicity and those that do not. By calibrating my geomechanical models in this manner I can determine those that are likely to give good predictions going forward, and thereby assess the risks of leakage due to deformation. The ability to link geophysical data, geodetic data (surface deformation), and geological information to build geomechanical models is crucial for determining the risks of leakage due to deformation. Computer models of geomechanical deformation can be used to determine how the shape and material properties of the reservoir influence the mechanical response. This will be useful in selecting sites that will not be at risk from deformation, and in designing injection regimes that minimise risk of leakage through fractures. My overall aim is to generate a manual of best practice for dealing with geomechanical deformation at CCS sites. The project will be conducted in collaboration with the operators of the In Salah fields, BP and the Geological Survey of Canada. The EU intends to implement at least 12 CCS demonstrations projects by 2015, so my project is timely in that it will provide a manual of best practice for dealing with geomechanical deformation before injection begins at these sites.