A review on shale gas prospect in Indian sedimentary basins

Shale gas is a natural gas trapped within shales, which are fine-grained sedimentary rocks. Hydrocarbons are generated from organic-rich shale under an optimal temperature-pressure condition due to basin subsidence. A part of the generated hydrocarbons migrates and gets trapped in conventional reservoirs that can be produced commercially by standard techniques. Shale can act as both source and reservoir rocks. Depending on the type of organic matter and maturation level, unconventional hydrocarbons could be shale oil or shale gas or a combination of both. There is a sizeable deposit of shale formations in several sedimentary basins of India with different total organic (TOC) content and maturity history. The Cambay, Krishna-Godavari, Cauvery and Damodar valley are the four major basins of shale gas reservoirs as indicated by considerable thickness of shales; sufficient TOC (2 to 6 wt%) content; and good thermal maturity with vitrinite reflectance of more than 1.0. The Vindhyan, Upper Assam, Pranhita-Godavari and Rajasthan basins are other prospective basins that need to be probed by geo-scientific methods. The gas in these shale reservoirs can occur within the natural fractures or pore spaces or as adsorbed gas on the organic matter. This is considered as the next generation major energy resource after gas hydrates and coal bed methane.