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ABSTRACT
Ensuring long-term containment of CO2 is critical for a safe geological storage of carbon. Although Carbon Capture and Storage (CCS) is feasible in depleted hydrocarbon fields, it can pose significant risk to safety and the environment if its containment is not ensured. An integrated geomechanics workflow to evaluate caprock integrity is presented in this paper. This approach integrates reservoir simulation which typically computes variation in formation pressure and temperature with geomechanical simulation which models variation in stresses. Coupling between these two simulation modules is done iteratively until an equilibrium state between formation pressure and stress is achieved within a given tolerance. The efficiency of this approach is demonstrated through a case study of a proposed carbon storage site in Canada where an injection rate of 600 tonne/day for 25 years is planned.

INTRODUCTION
Carbon Capture and Storage (CCS) in the form Enhanced Oil Recovery (EOR) has emerged in recent years, as one of the most efficient options to reduce industrial greenhouse gas emissions. Although CCS is feasible in highly porous and permeable formations of depleted hydrocarbon fields, it can pose significant risk to the safety and the environment if it is not contained properly within the reservoir for a long time [Holloway, 1997]. Since CO2 is less dense than water, the targeted injection site should be overlain by a formation, typically shale which has low-permeability and high competence to withstand the upward buoyancy-driven force of the injected CO2 [Torp and Gale, 2004]. On the other hand the density difference between CO2 and formation water at reservoir conditions can create excessive pressure on the sealing formation which can induce fractures or can potentially reactivate existing fractures or faults. Ensuring long-term containment of CO2 is critical for a safe geological storage of carbon dioxide. Geomechanical containment capability of a seal depends on the state of stress acting on the storage medium, and the strength of the seal formation.

Geomechanics plays an important role in the selection, design, and operation of a storage facility and can be of significant benefit in optimizing engineering performance, maintaining safety and minimizing environmental impact. In this paper, we present an integrated geomechanics workflow to evaluate caprock integrity. This approach models the virgin and the altered state of stress using a finite element based reservoir geomechanics software, VISAGE and the variation in formation pressure and temperature using reservoir simulator, ECLIPSE. The iterative coupled computations between these two simulation modules continue until an equilibrium state between pore pressure and stress is achieved within a given tolerance. The efficiency of this approach is demonstrated through a case study of a proposed carbon storage site in Canada where an injection rate of 600 tonne/day for 25 years followed by a 500 years of shut-in time is planned.