8.3 Tasks accomplished
This part consists of the tasks accomplished at Sleipner CO2 sequestration operation during the SACS project and the experiences of monitoring the carbon dioxide storage. Four main work areas of the SACS project include:
• Microseismic studies
• Characterisation of the reservoir and caprock
• Monitoring the CO
injection process
• Reservoir simulation and
• Geochemical characterisation
8.3.1 Micoseismic studies
The natural state of stress due to the geological setting, the mechanical properties of the reservoir rocks and host rocks, and the changes in pore pressure due to fluid withdrawal or injection are the principal causes of induced seismisity in a reservoir in which there is fluid movement. Detailed study on the literature review of the state of stress in the North Sea as well as observations on the occurrence of microseismisity is presented in SACS-Feasibility study of microseismic monitoring (Fabriol, 2001). Here the main conclusions drawn from the study follow.
The study suggests that the conditions that could promote seismic slip along natural faults or fractures at Sleipner include: the regional compressive stress regime, because of which faults, whether present and depending on their orientation with respect to the maximum horizontal stress (SHmax), can be critically stressed fractures; the slight overpressure due to injection of CO2, which is added to the hydrostatic pressure, Carlsen et al. (2001) predict an overpressure of 0.02 MPa due to the accumulation of CO2 in the space confined by the caprock; and stress variations as slight as 0.02 MPa (in compressive region), are common examples of triggering failure (e.g. King et al., 1994).
8.3 Tasks accomplished
This part consists of the tasks accomplished at Sleipner CO2 sequestration operation during the SACS project and the experiences of monitoring the carbon dioxide storage. Four main work areas of the SACS project include:
• Microseismic studies
• Characterisation of the reservoir and caprock
• Monitoring the CO
injection process
• Reservoir simulation and
• Geochemical characterisation
8.3.1 Micoseismic studies
The natural state of stress due to the geological setting, the mechanical properties of the reservoir rocks and host rocks, and the changes in pore pressure due to fluid withdrawal or injection are the principal causes of induced seismisity in a reservoir in which there is fluid movement. Detailed study on the literature review of the state of stress in the North Sea as well as observations on the occurrence of microseismisity is presented in SACS-Feasibility study of microseismic monitoring (Fabriol, 2001). Here the main conclusions drawn from the study follow.
The study suggests that the conditions that could promote seismic slip along natural faults or fractures at Sleipner include: the regional compressive stress regime, because of which faults, whether present and depending on their orientation with respect to the maximum horizontal stress (SHmax), can be critically stressed fractures; the slight overpressure due to injection of CO2, which is added to the hydrostatic pressure, Carlsen et al. (2001) predict an overpressure of 0.02 MPa due to the accumulation of CO2 in the space confined by the caprock; and stress variations as slight as 0.02 MPa (in compressive region), are common examples of triggering failure (e.g. King et al., 1994).
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