oa Characterisation and Genesis of Oils from Unconventional Reservoirs of Ahmedabad Block, Cambay Basin, India

Cambay Basin is endowed with hydrocarbon accumulations in multiple reservoirs of different ages. In<br>Ahmedabad block reservoirs within Kalol Formation can be identified on conventional logs whereas<br>reservoir rocks in Cambay Shale are predominantly shaly and unconventional in nature with no<br>identifiable reservoir manifestations on well logs in fields like Sanand, Jhalora, Wadu and Indrora. The<br>problem of identification and quantitative evaluation of such unconventional reservoirs is being<br>addressed by high resolution Resistivity Imaging Tool. Identification of hydrocarbon zones is an<br>arduous task in such reservoirs but at the same time source of hydrocarbons is also a relevant issue.<br>The present work is to see if these reservoirs are self sourced or have migrated hydrocarbons.<br>Oils from unconventional shale reservoirs, developed in Chhatral Member of Younger Cambay shale in<br>Sanand field in Ahmedabad block have been characterized and correlated with oils from other<br>reservoirs. Source rock identification and characterization has been carried out from these and nearby<br>wells using pyrolysis, isotopic and biomarker studies.<br>It has been found that oils in these unconventional reservoirs are genetically similar to the oils in<br>conventional reservoirs from the same and nearby wells. The source rock is either absent in these<br>shales or not mature enough to generate hydrocarbons indicating that hydrocarbons from more mature<br>Cambay Shale or Olpad have migrated to these locales and is not in-situ generated.