Nihar Ranjan Kar, Devleena Ranjan Kar Mani, Soumyajit Mukherjee, Swagato Dasgupta, Mohit Kumar Puniya, Mery Biswas, Soumyajit Mukherjee

Hydrocarbon exploration and production are going on in Barmer basin (Rajasthan, India) for
more than a decade. The potential source rocks are of Paleocene – Eocene age, and Mesozoic
siltstones form the reservoirs. The western and central portions of the Rajasthan basin are
characterised by extensive lignite formations, which can be promising for artificial
transformation to oil and gas. We study the source rock properties, depositional environments
and hydrocarbon generation potential of the Paleogene lignitic shales of the Giral lignite mine
and the Cretaceous Sarnu siltstones for their source and reservoir rock potentiality. The total
organic carbon content (TOC) of the Giral samples range between 0.76-49.83 wt% and the
thermal maturity, as reflected by the pyrolysis Tmax, lies between 412-468 ℃. Sarnoo siltstones,
on the other hand, have a very low TOC ranging from 0.02-0.08 wt% and a Tmax of 320-608 °C.
The higher TOC and a lower oxygen index (OI) of Giral lignites and shaly lignites indicate the
prevalence of a reducing depositional environment. Bulk organic geochemical parameters
involving kerogen pyrolysis and thermal degradation kinetics indicate a more promising
hydrocarbon generation potential in the lignite than shales, which, however exhibits higher
thermal maturity of organic matter. Giral lignites as well as shales show dominantly Type-III heterogeneous kerogen, which is sourced from terrestrial organic matter. This is also corroborated by a broader distribution of activation energy derived from the thermal decomposition of the kerogen. The kerogen transformation ratio (KTR) and the hydrocarbon generation rate GR) suggest a considerably earlier and quicker kerogen transformation. Samples from the Sarnoo area offer no significant information on the source rock characteristics, due to their lean organic nature. However, lignites and shaly lignites of the Giral mine are identified as excellent candidates for their suitability towards easy conversion into hydrocarbon
products through artificial techniques.