Geological CO2 sequestration in multi-compartment reservoirs:
Geomechanical challenges
N. Castelletto, G. Gambolati, P. Teatini
Dept. of Civil, Environmental and Architectural Engineering,
University of Padova, Padova, Italy
Sequestration of large amounts of CO2 within deep underground reservoirs has been
proposed as a potential approach for reducing atmospheric emissions of greenhouse
gases. A CO2 sequestration project should address the associated environmental and
safety issues and, in this respect, the importance of geomechanics has recently been
widely recognized. Geomechanics is even more important when fluid injection is planned
in faulted reservoirs. How much CO2 can be safely injected into multi-compartment
reservoirs? Are geomechanical constraints more restrictive than flow-dynamic
constraints? These and other questions are addressed in the present study using a
three-dimensional finite element-interface element geomechanical model. We simulate
the possible mechanical failure in both the injected formation and the caprock, the
fault/thrust reactivation, and the ground surface displacement in a faulted reservoir of the
offshore northern Italy, where seismic surveys provided an accurate characterization of
the faulted geological structure. Based on reliable petrophysical/geomechanical properties
from well logs and pore overpressure as predicted by a fluid-dynamic model, the results
show that the injection of 1x106 ton/a of CO2 may be performed over a few years only.
Thereafter, part of the injected formation fails by shear stress. A number of parametric
scenarios are investigated to address the major uncertainties on the geomechanical
response to CO2 injection. The modeling outcome suggests that shear failure and
faults/thrusts reactivation can occur much before attaining the hydraulic fracturing
pressure, hence representing two major constraints for a safe and permanent containment.
