Still or sparkling: Microseismic monitoring of CO2 injection at In Salah

It is possible to capture emissions of CO2 from coal fired power plants and storing 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. 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 the emission of seismic energy from reactivated fracture networks. By detecting these microseismic emissions, it is possible to determine how the subsurface is responding to CO2 injection. We propose a study of microseismic events induced by geomechanical deformation at the In Salah pilot CCS project, Algeria. This project presents an excellent opportunity to study the utility of using microseismic monitoring to image geomechanical deformation induced by CO2 injection. 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. Geomechanical deformation at In Salah is inferred from the uplift of the ground surface above the reservoir. Geomechanical models based on surface deformation data at In Salah have been used to estimate the deformation occurring in the reservoir. Microseismic observations will provide a much more direct image of deformation of the reservoir. We will use event locations to calibrate and benchmark geomechanical models, distinguishing between models that do a good job of predicting microseismicity and those that do not. By calibrating our geomechanical models in this manner we 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, and forms a key goal of this project. Thus far one CCS site (Weyburn) has deployed microseismic monitoring. The Bristol Seismology Group were able to use the microseismic data to greatly improve our understanding of the ongoing geomechanical processes in the reservoir. The EU intends to initiate at least 12 CCS sites by 2015, many of which may deploy microseismic monitoring. This project is therefore very timely in that it is necessary to assess the feasibility of this (and other) monitoring techniques before large-scale CCS operations begin. Our experience with microseismicity at Weyburn means that Bristol University is ideally placed to conduct this research, as we will be able to draw on previously acquired knowledge to compare and contrast microseismicity at the two different CCS sites, and thereby come to more general conclusions regarding the deployment of microseismic techniques to monitor CCS.