Hydrous pyrolysis of New Albany Shale: A study examining maturation changes and porosity development

The characterization of nanoscale organic structures has improved our understanding of porosity development within source-rock reservoirs, but research linking organic porosity evolution to thermal maturity has generated conflicting results. To better understand this connection, an immature (0.25% solid bitumen reflectance; BRo) sample of the New Albany Shale was used in four isothermal hydrous pyrolysis (HP) experiment sequences at 300 degrees, 320 degrees, 340 degrees, and 370 degrees C, with residues collected periodically for a maximum of 103 days. The HP residues, along with the original immature sample and two naturally matured (1.49 and 1.56% BRo) New Albany Shale samples were analyzed for organic petrology, total organic carbon (TOC) content, and organic porosity evaluation using correlative light and electron microscopy (CLEM). All of the HP series increased in thermal maturity with increasing duration of pyrolysis, though reflectance for each series plateaued within 25 days of maturation. Initially, TOC in the HP residues decreases (from 14.24 wt. %) with increasing thermal maturity until similar to 1.0% BRo where TOC remains at similar to 9-10 wt. % for all remaining residues. Qualitative CLEM observations within the 50-100 day 300 degrees and 340 degrees C HP sequences (0.95-1.70% BRo), and the naturally matured samples, develop organic porosity in smaller (<5 mu m in diameter), void-filling solid bitumen that occurs in spaces between clays and other fine-grained minerals. The 370 degrees C HP residues developed significant organic porosity, relative to the other HP temperature series in all solid bitumen accumulations regardless of size. Overall, the study indicates that temperature and duration of artificial maturation play an important role in the abundance of pores in the HP residues. This work expands on our understanding of the conditions needed for the generation and development of organic porosity in the New Albany Shale and potentially in other marine source-rock petroleum systems.

Automated summary

Research on immature New Albany Shale samples using isothermal hydrous pyrolysis experiments showed that organic porosity increases with thermal maturity, while total organic carbon content stabilizes after a certain point. The development of organic porosity varied at different temperatures, indicating the importance of temperature and duration of artificial maturation on pore abundance in the samples.