Muhammad Zulqarnain, Stephen O. Sears, Mehdi Zeidouni, Richard G. Hughes, Louisiana State University; Douglas Carlson, Louisiana Geological Survey
One of the key requirements of a commercial scale carbon sequestration site selection process is identifying injection sites to safely inject and retain injected CO₂ over extended time scales. This requires thorough evaluation of site-specific surface and subsurface features. A site screening and selection framework was developed and used to screen three potential sites in South Louisiana, incorporating surface data such as source distance, proximity to populations centers and state lands, land usage, legacy oil and gas well data, and regional geologic trends. This study focuses on Miocene strata between depths of 3,000 ft or USDW depth (whichever was deeper) and the start of the geopressure depth.
Regionally the Miocene sediments thicken and dip towards the south, reflecting a prograding deltaic environment during the Miocene which resulted in the deposition of thick packages of fine-grained sandstones suitable for CO₂ storage.
Three sites that are spatially separated with varying subsurface geological features were analyzed. Sites 1 and 3 are located in the South-East and South-West regions of Louisiana , and Site-2 is in a central location. All three sites are located south of Interstate Highway 10 , avoid large well density areas and include state lands or state water bodies.
The modeled storage zone at Site -1 is located at depth of 7,500ft, and has a structural dip of 1.4 degrees. The depositional environment is interpreted to be a Middle Miocene wave dominated delta. The storage zone has a net sand thickness of 230 ft, and a porosity of 31%, providing substantial storage capacity. The primary seal has a thickness of 304 ft thick which is expected to provide an effective stratigraphic trap. The storage zone at Site-2 is located at a depth of 9,500ft with a dip angle 1.7 degrees and a Middle Miocene fluvial dominated deltaic depositional setting. The storage zone has a net sand thickness of 160 ft and a porosity of 30%. A good quality 336 ft thick primary seal is expected to provide adequate stratigraphic trapping capabilities. The modeled zone at Site-3 has an average depth of 7,800 ft, a dip of 3 degrees and lies in the Lower Miocene. It has a fluvial dominated deltaic depositional setting. This is a massive stacked sand complex with a net sand thickness of 860 ft and a porosity of 33%, resulting in excellent storage capacity. The quality of the primary seal is lower than Sites 1 and 2, with an average thickness of 90 ft. Effective storage at this site will have to rely on hydrodynamic trapping rather than a stratigraphic trap.
The screening framework presented in this study and the detailed evaluation of three specific sites in South Louisiana provide useful insights into how to screen sites and the suitability of these Miocene sediments for commercial scale CO₂ storage projects. It is envisioned that the presented analysis will be beneficial for a large number of audiences involved in the CCUS work and aid in site selection.