| Popis: |
Saline aquifers are the most promising target for underground CO2 sequestration since they have the largest capacity compared to other possible locations, for example coal seams or depleted gas and oil fields. One of the major risks associated with sequestration in aquifers is the potential leakage of CO2 through cap rock and overburden leading to escape of CO2 into shallow potable aquifers or to the atmosphere. Factors responsible for rock failure need to be investigated before starting a CO2 injection program to avoid potential leakage problems. This paper presents a novel approach for assessing and mitigating the risk of CO2 leakage caused by geomechanical effects. An equation-of-state compositional and GHG (Green-House Gas) simulator has been modified to incorporate iterative coupling with an in-house geomechanical code (geomechanics module). The coupled model is used to predict possible leakage events during an injection process. The following steps are taken to solve the problem: The reservoir simulator computes the amount of CO2 dissolution and flow in the formation, geochemical reactions, and changes in pressure, temperature and compositions.Based on the values of pressure and temperature at the end of every time step, the geomechanics module computes stress change and deformation in the formation and its surroundings to determine if and where rock failure might occur.A Barton-Bandis model is used to simulate opening and closing of fractures in the cap or country rock due to development of stresses caused by high injection pressure. Example cases are presented to demonstrate the workflow and to show how injection scenarios may be altered to mitigate the risk of leakage. Both isothermal and non-isothermal situations are examined. |
