IMPACT OF MATURATION PROCESSES ON ORGANIC MATTER IN SHALES: IMPLICATION FOR GEOLOGIC CARBON SEQUESTRATION

The Middle Bakken has low porosity and permeability, which makes Bakken shales an attractive candidate for geologic CO2 sequestration. Previous studies have shown that unconventional reservoirs, such as Bakken shales, provides viable potential for geologic CO2 storage after depletion through primary production. In this study, we experimentally assess how the maturation-induced modified properties of organic matter will impact geologic CO2 storage in shales.

We utilized artificially matured Bakken shale samples kept in the oven at 340°C with increasing thermal maturity (T_max419-445°C). Firstly, we analyzed the shale samples to evaluate the altered geochemical properties. Secondly, we conducted scanning electron microscopy to characterize alterations in the texture and distribution of organic matter. Subsequently, we utilized a reflected light microscope for advanced microstructural characterization of the morphological modifications. Lastly, we showed the geologic CO2 storage implication of the modified geochemical and microstructural properties due to impact of maturation process on organic matter.

Our analysis from the geochemical results show alterations in the total organic carbon content (TOC) and hydrogen index, and this alteration continue with increasing thermal maturity. The microstructural analysis also shows reduction in the pore structure of the shale rock. Consequently, the alterations in TOC and microstructure of the Bakken Shales due to the impact of the maturation process, improves its suitability as a caprock in conventional trapping scenarios, or as a CO2 storage medium itself after depletion.