Insights from Optical-Electron Correlative Microscopy on Shales Subjected to Underground Thermal Treatment

ABSTRACT Extracting hydrocarbons from low-permeability shale is challenging. While hydraulic fracturing is typical, it poses environmental risks. This study explores underground thermal treatment (pyrolysis) using optical-electron correlative microscopy on an organic-rich shale from the Permian Barakar Formation, Rajmahal Basin, India. Thermal treatment (350–650°C) expanded liptinite pores (10 – 294 μm), while inertinite retained primary pores, and vitrinite showed no SEM-detectable pores. At 650°C, extensive pore enlargement and rupture indicate hydrocarbon expulsion. These findings provide key insights into maceral-specific porosity evolution, improving understanding of in-situ thermal treatment for unconventional hydrocarbon recovery.