Role of Boundary Condition On Long Term Storage of Carbon Dioxide in Deep Saline Formations

Deep saline aquifers have been identified as proper and viable domains for CO₂ storage. They offer the largest storage potential and are distributed worldwide in all sedimentary basins. Therefore, these make them a very attractive option, although most of them may not have been extensively characterized.

The lack of characterization of deep saline aquifers generates uncertainties on petrophysical properties, particularly the extent and boundaries of the reservoir. Information regarding the extension and boundary conditions of a deep saline formation plays an important role in quantifying the amount of CO₂ that can be injected into the formation, as well as pressure variations within the system. This could ultimately affect the trapping capabilities of the confining unit, representing the risk associated with pressure gain due to CO₂ injection in the geological formation.

This study asses the viability of CO₂ sequestration in a geological formation as a “safe” and long term solution. Therefore, this work focuses on the effects that different types of boundary condition have on an ongoing CO₂ storage project, in a deep saline aquifer located in the Citronelle field in Mobile, Alabama. The injection in this field is taking place since August 2012 and is planned to continue for 3 more years.

A full field reservoir model was built using information from the actual field site. This information included well log, core analysis and SCAL data. Reservoir scale simulations were performed. According to the results it was observed that when the imposed boundary condition consists of a constant pressure boundary, the average reservoir pressure eventually stabilizes back to the initial reservoir pressure, opposed to when the boundary condition consists of a no-flow condition. When a no-flow boundary is imposed to the system, a pressure gain is observed and varies with the properties of the confining unit. Apart from the mentioned properties, the size of the reservoir is an important factor affecting the pressure gain. A detailed study has been performed to show the pressure variations in the system under the specific imposed conditions.