Global review on shale: Focus on hydrocarbon geoscience & carbon sequestration

Shale gas is a potential unconventional resource meeting the challenges of the energy crisis. Among the 195 countries of the world, 52 countries contain 108 established shale basins and 156 shale formations for commercial shale oil and gas exploration. For commercial development, the following factors are important- (i) thickness of the shale formation and their depths, (ii) (low) permeability of the cap-rock / seal, and (iii) geochemical and hydraulic properties of potential organic-rich source rocks. The carbon sequestration potential is unique to each hydrocarbon potential shale formation and basin. Shale formation designated as tight rocks act as storage/reservoirs for carbon sequestration as it captures CO2 permanently and does not permit it to move upward across the seal. This reduces atmospheric emission level and has potential to check global warming. However, CO2 capture in shale has not been in global focus for researchers. The study of the prospective shale oil and gas formations worldwide reveals that hydrocarbons are found within 3280–16,500 ft (999.74–5029.2 m) depth. Their average total organic carbon (TOC) and thermal maturity range from 1 % to 10 % and 0.6–3.8 %, respectively, for original type I and II kerogens. The geologic CO2 sequestration process in potential and active shale basins are discussed with respect of several tectonic events, and past climatic changes such as glacial and interglacial periods and sea-level variation. The Russian Bazhenov Formation is the world’s most prosperous hydrocarbon reservoir while the black organic-rich shale in the Vaca Muerta Formation (Neuquen basin, Argentina) ranks second.