TGS analyzes two prolific formations in the Gulf Coast Basin, the Frio and Lower Cotton Valley
As carbon capture and storage (CCS) accelerates across the Gulf Coast, regional initiatives are gaining momentum—from ExxonMobil’s expansion along the Houston Ship Channel to new DOE-backed CCS hubs in Texas and Louisiana. Companies like Chevron, Talos, and Shell are rapidly developing infrastructure to sequester millions of tons of CO₂ annually, while regulatory frameworks and community engagement continue to evolve. In this dynamic landscape, high-resolution subsurface insights are essential. TGS recently announced the completion of their Gulf Coast CO₂ Storage Assessment project in the region. This assessment provides the detailed, core-calibrated petrophysical data needed to evaluate major formations in the basin, helping operators prioritize safe, efficient, and scalable storage projects in areas where CO₂ capacity is promising. This article explores the geological viability and strategic value of two key formations, the Frio and the Lower Cotton Valley. Each offers distinct geological traits that shape their capacity, efficiency, and practicality for carbon storage.
The Frio Formation, found across Texas and Louisiana, is a standout candidate due to its favorable reservoir characteristics. In regions where storage capacity exceeds 5 Mt per square kilometer, it has a cumulative CO₂ storage capacity of approximately 4,151,098 Mt and covers 15,688 square miles, or 40,632 square kilometers (Figure 1). The formation features an average net thickness of 707 feet, reaching a maximum of 2,055 feet. With an average porosity of 27% and permeability of 150 millidarcies (mD), the Frio supports efficient injection and movement of CO₂. It maintains moderate subsurface conditions, with an average temperature of 142°F and pressure of 2,857 PSI. However, its high salinity – averaging 157,751 ppm – poses operational risks such as scaling and corrosion.
Key benefits of the Frio Formation for CO₂ storage include its high porosity and permeability, which facilitate large-volume injections and enhance storage effectiveness. Its wide geographic distribution adds flexibility for siting projects. Moderate pressure and temperature conditions make the formation more accessible and reduce the complexity of well design and monitoring systems. On the downside, the high salinity environment demands corrosion-resistant infrastructure and thorough monitoring to ensure long-term storage integrity.
Figure 1. Analysis of the Frio Formation in Texas and Louisiana. Areas where CO₂ storage capacity exceeds 5 Mt were used in the analysis and are highlighted in the maps. Also included for reference are porosity and net thickness for the Frio Formation.
The Lower Cotton Valley Formation, stretching across Arkansas, Mississippi, and Alabama, offers even greater CO₂ storage capacity – estimated at 6,130,456 metric tons – over a broader area of 16,891 square miles, or 43,747 square kilometers. It features an average net thickness of 865 feet and can reach up to 2,478 feet. The formation has lower average porosity (16%) and much lower permeability (1.64 mD) than the Frio, which can impact injection rates and overall efficiency. However, it benefits from slightly lower salinity levels (127,954 ppm), reducing the risks of scaling and material degradation. The formation exists in deeper and hotter zones, averaging 170°F in temperature and 4,450 PSI in pressure.
Despite its lower permeability, the Lower Cotton Valley Formation is a strong candidate for CO₂ sequestration due to its large storage volume and lower salinity. Its greater depth and pressure can help keep CO₂ in a supercritical state, improving its storage density and minimizing plume migration. However, the formation's heterogeneity and challenging subsurface conditions require advanced modeling and engineering solutions to optimize CO₂ injection and ensure containment.
When comparing the two, the Frio Formation offers easier injection conditions due to its higher permeability and porosity, but its high salinity and historical production activity may introduce complexities. In contrast, the Lower Cotton Valley presents a higher overall storage potential with reduced salinity issues, though its low permeability and more extreme subsurface conditions demand more intensive planning and infrastructure.
Figure 2. Analysis of the Lower Cotton Valley Formation in Arkansas, Mississippi, and Alabama. Areas where CO₂ storage capacity exceeds 5 Mt were used in the analysis and are highlighted in the maps. Also included for reference is porosity and net thickness for the Lower Cotton Valley Formation.
In conclusion, both formations are strategically important for regional carbon storage initiatives in the Gulf Coast Basin. The choice between them should be driven by specific project goals, whether prioritizing injection ease and monitoring or maximizing long-term storage capacity and containment security.
