Coupled Flow and Deformation Modeling of Carbon Dioxide Migration in the Presence of a Caprock Fracture during Injection

Understanding the transport of carbon dioxide (CO2) during long-term CO2 injection into a typical geologic reservoir, such as a saline aquifer, could be complicated because of changes in geochemical, hydrogeological, and hydromechanical behaviour. While the caprock layer overlying the target aquifer is intended to provide a tight, impermeable seal in securing injected CO2, the presence of geologic uncertainties, such as a caprock fracture or fault, may provide a channel for CO2 leakage. There could also be a possibility of the activation of a new or existing dormant fault or fracture, which could act as a leakage pathway. Such a leakage event during CO2 injection may lead to a different pressure and ground response over a period of time. In the present study, multiphase fluid flow simulations in porous media coupled with geomechanics were used to investigate the overburden geologic response and plume behavior during CO2 injection in the presence of a hypothetical permeable fractured zone in a caprock, existing or activated. Both single-phase and multiphase fluid flow simulations were performed. The CO2 migration through an existing fractured zone leads to changes in the fluid pressure in the overburden geologic layers and could have a significant impact on ground deformation behavior. Results of the study show that pressure signature and displacement patterns are significantly different in the presence of a fractured zone in the caprock layer. The variation in pressure and displacement signatures because of the presence of a fractured zone in the caprock at different locations may be useful in identifying the presence of a fault/fractured zone in the caprock. The pressure signatures can also serve as a mechanism to identify the activation of leakage pathways through the caprock during CO2 injection. Pressure response and ground deformation behaviour from sequestration modeling could be useful in the development of smart technologies to monitor safe CO2 storage and understand CO2 transport, with limited field instrumentation.