Assessing the potential for CO2 sequestration of a saline aquifer in the Frio Formation, South Texas, USA

Abstract

The Frio Formation onshore Texas, USA, represents a significant target for CO₂ storage, and South Texas particularly has experienced an increased interest. This study evaluates a 100,000-acre area containing a ∼5000-foot-thick, sand-prone reservoir bounded by sealing normal faults. Reservoir connectivity, porosity, and permeability vary, with permeability potentially impacted by volcanic and carbonate content. The study addresses the need for reliable methods to evaluate storage potential in reservoirs with limited data, but located adjacent to legacy oil-gas activity. We provide a practical workflow to assess CO₂ storage in saline aquifers, producing defensible storage capacity estimates without requiring full reservoir modeling, while still accounting for reservoir heterogeneity and fault compartmentalization.

To define the site's structural configuration and stratigraphic framework, 3D and 2D seismic mapping were performed, as well as well-log correlation to subdivide the Frio stratigraphy into seven reservoir zones. Depositional facies analysis provided insights into sand distribution, lateral reservoir continuity, and sand presence in the syncline down-dip of the main rollover anticline. Petrophysical analysis characterized reservoir quality within the injection interval. Rock quality is emphasized due to its critical role in reservoir injectivity within the Frio section.

This comprehensive geological evaluation informed the CO₂ pressure-based capacity calculations, estimating 460 million metric tons of storage potential within the Frio, in the area of interest. The study highlights the value of integrated methodologies and tailored approaches for assessing realistic CO₂ storage capacities, offering practical solutions for South Texas storage and a comprehensive methodology for incorporating data from past oil-gas development to saline formations.