Reservoir quality evaluation as a measure to forecast hydrocarbon and CO2 storage prospects in Irati and Rio Bonito Formations, Paraná Basin

Enhanced hydrocarbon recovery processes coupled with CO₂ storage are, by far, the cheapest carbon capture and storage (CCS) options in geological structures. However, reservoirs are also being explored for CO₂ storage in regions without producing/depleted hydrocarbon reservoirs, such as the Irati and Rio Bonito Formations in the southwestern part of São Paulo. Therefore, the study involves petrophysics-based flow unit factors to predict the reservoirs’ quality, primarily focusing on hydrocarbon viability with CO₂ storage possibilities based on the shale, carbonate, sandstone and siltstone rock units. The methodology involving the models for the research objective is uncommon for the Irati and Rio Bonito Formations. The porosity range is 0.02 to 0.15 in shales, 0.028 to 0.18 in siltstones, 0.03 to 0.21 in carbonates, and 0.10 to 0.31 in sandstones based on the sonic-density porosity (Ф_S-D) approach. Permeability (k) is 0.00005mD to 36.6mD in shales, 0.0008mD to 132mD in siltstones, 0.025mD to 786mD in carbonates and 8mD to 10000mD in sandstones. The results show more significant fluid transmission indices for the sandstone based on Ф, k, free fluid index-FFI, reservoir quality index-RQI, and flow zone indicator-FZI. Also, the parameters are considerably significant for carbonates in some instances, less effective for siltstone and comparatively insignificant for shale. However, shales` total organic content (TOC) values are up to 10.5%, suggesting their hydrocarbon generation potentials. Significant values (e.g., Ф ≥25% and FFI ≥20%) in sandstones indicate reservoirs with the potential for hydrocarbon accumulation. Considerable physical qualities, as presented for the sandstone, suggest reservoir rock units with reasonable fluid (e.g., gas) recovery and CO₂ injection rates. Therefore, based on the research results, the Irati Formation shales are viable hydrocarbon source rocks, and the Rio Bonito Formation sandstones are potential hydrocarbon reservoirs. Subsequently, future hydrocarbon production events will enhance CO₂ storage options in the region. Furthermore, the research results may serve as input data in related hydrocarbon exploration studies. However, if further research indicates non-commercially viable hydrocarbon reserves, the findings will also aid in delineating dedicated geological reservoirs for CO₂ storage when needed.